I purchased a set of Panasonic cordless phones from woot.com a while back, and all of them worked great. But, after a while, one of the chargers stopped working. Looking at the voltage on the charger, it was showing the normal voltage across it (about 5.5V), but the unit just wouldn’t charge. I wired up the unit with my meter between checking amperage draw, and it was only pulling about 2mA, where a working charger showed 200mA. Hmmm…
I opened the charger (single screw on the bottom) and it’s pretty darn simple, as you can see from the picture. The 1R resistors both checked out, as did the fuse, but interestingly, I was seeing a 1.8V drop across the protection diode. That’s… not right. I opened another unit and got the normal 0.6V drop across it.
So, figured the diode might be bad, I pulled it, and got the more normal 0.6V drop. So, bad solder joint it would have seemed. I put it back in, and soldered it back in, and it stayed with the 0.6V drop. I hooked it all back up, and meter showed a more normal 200mA draw. So, it works!
Obviously, given the look of the board, I’m guessing these are cranked out by the thousands, and just ended up with a cold solder. So if you have one of these, check that protection diode (as well as the fuse), since it’s unlikely the resistors would go south. =)
UPDATE 7/3/2014As can be told from the comments, I’ve had the repair fail since doing it. Resoldering the diode would help for a bit, then it would fail again. So, knowing the diode was the issue, I grabbed a standard axial 1N4001 from the parts bin, trimmed the legs, bent them over, and soldered it in place. So far, it’s working… but I’m not going to consider it fixed until it lasts for a good month or so. I have to wonder, since I can’t find any stats on that diode, if it’s overheating (and therefore, under-spec, but that generally wouldn’t cause the symptoms seen). And yes, I know it looks like hell. I don’t care. =)
drew says
Thanks for the info.
Albeit having good voltages all around and the nominal .6 volt drop across the zener, I resoldered the zener just in case, on a hunch.
So far, so good. That seems to have fixed the problem.
It’s amazing how a simple 1 fuse, 2 resistors, 1 zener diode series circuit can cause such grief.
Once again, thank. Ain’t the internet grand.
Drew.
staze says
Indeed. I’m actually amazed someone (you) found this article after I’ve only had it posted a few days, and managed to fix their charger. =) And yes, the internet is quite grand. =)
Drew says
Alas my victory was shortlived.
The charger worked fine for a day and then went bad.
Instead of indicating “fully charged” it continually displayed “charging” but I suspect that it wasn’t charging or not charging at the correct amps because after a few days my phone was fully discharged.
I still suspect a bad zener diode though, and as a trial, I bypassed it. So far it’s indicating “charging” and should reach full charge in a day or so.
If my experiment works, I’ll simly replace the zener with another one, in what I believe to be a 1n1314.
Drew
staze says
Yup, mine did the same thing. Would say “charging” but only down at the bottom, and then would drain the battery over a couple days. Cursory inspection showed everything was fine… right voltages, etc. Wasn’t until I measured amps that I saw it was clearly busted. Re-soldering mine seems to have fixed it, but I’ll keep an eye on it. Obviously a cold joint would slowly cause heat build up to the point of it not working. Anyway, I’ll have to check mine when I get home and see if it’s still working…
Is it actually a zener? Mine is marked 1241 M25. I’m guessing 1241 is a date code (41st week of 2012), but I can’t find anything for M25. A 1n1314 is an 11v zener, so that doesn’t make much sense either. But, I didn’t really check to see what the voltage was on each side of the diode, so I can’t say I know one way or the other. I just assumed it was a protection for reverse polarity, or the phone somehow sending a voltage back through the charger. If you can find figure out the markings on the diode, let me know. =)
Drew says
First I’d like to apologize for the zener and 1n1314 bit. It was late, I was tired and obviously surfed where I shouldn’t have surfed and quoted stuff I should have quoted.
Now back to the problem. I couldn’t locate my exact model of phone. I did however locate service manuals for similar models (models that had charger units). In all cases, the schematic was real simple. Like ours it consisted basically of a fuse, a couple of resistors and a diode ….. yup a diode.
They all quoted part number Panasonic B0JAME000095 Diode ….. good luck with that one.
The diode theory makes sense cause it’s simply used as protection to prevent a reverse voltage.
My experiment of bypassing the diode, albeit a short term fix, also makes sense cause it takes the diode out of the equation.
If it continues to work, I think finding and replacing it with a similar value diode should fix the problem.
The quest for the repair continues.
Drew
staze says
Indeed. And I doubt reverse voltage would ever really be an issue unless something really dumb happened.
Mine is still working, so the resoldering seems to have still “fixed” it, but no clue. I would assume any 1n4001 or similar would probably work. We’re not talking huge voltages here. =) Heck, a simple NPN transistor wired up as a diode would probably work too. =P
Let me know if you find anything… =)
staze says
well… mine just stopped working. it’s back to just “charging” and never going to fully charged.
going to take it back apart and take a look, but it’s a bit of a conundrum. Generally, diodes don’t partially fail: they either short, or open. very odd.
I’ll have to dig through my parts and find a 1n4001 or the like to throw in there and see if that fixes it. going to try to re-solder the one first to see if that brings it back to life. Almost wonder if there’s some strain on the board from the removal and replacement of the phone. =/
Drew says
Its been over 5 days since I bypassed the diode using a piece of wire and the charger has been working fine. That indicates to me a bad diode. I agree with you though that a diode normally opens or shorts (in this case a short would have gone unnoticed and saved us from bypassing it) but for some reason this one seems to have failed in another way. I’m not to concerned about reverse voltage because the phone only sits in the charger in one direction. So for now, the diode bypass was the cheapest solution but I await your 1n4001 experiment results.
Thanks.
Drew
staze says
Drew,
Got the 1N4001 installed (per post update). So far, so good. Phone charged, and now says “Fully Charged” like it should. Yeah, it’s ugly, but who cares. =)
Ridgeland says
Me too. 🙁 I just replaced the diode with a 1N4002 (what I had). Voltage was 5.6V before the diode and 5.2V after the diode – both before and after replacing the diode. Now Kill-O-Watt shows 0.04 watt when the phone is set on the stand. Phone shows “Charging”. The phone was already charged in another base. In a minute or two the Kill-0-Watt drops to 0 watts but the phone is still displaying “Charging” not “Fully Charged”. Past efforts – took days before the phone starts complaining. I’ve spent weeks swapping around phone – base – power brick. Only thing consistent is the problem of not charging is always with the same base.
I’ll know within a week if the diode change cures the charging problem.
Thanks for this Blog.
staze says
Interesting… weird that the diode seems to be the common problem (though, the base really is only the diode… not like those 1R resistors are going to fail). Question for you, and previous commenter Drew: did you both get your phones from the woot.com offer a while back (or otherwise purchase them refurbished)? Curious if that’s why all these units were being refurbished in the first place, and Panasonic just didn’t do a good job diagnosing the issue to find a more long term fix.
Ridgeland says
Mine were purchased new from BestBuy for my Mom more than a year or two ago. I have them now. She had serveral issues with electrical power supply ( i.e. thunderstorms) and lost ethernet on the motherboard of her PC and more issues. That may have been be a factor.
I just checked now and my repaired base shows “Fully Charged” 🙂
Thanks again!
I read the specs of 1N4001 vs 1N4002 and the only difference I saw was one was 50V the other 100V. The supply is 5.6V so it doesn’t matter.
One spin is I was afraid the fat diode would cause the base to not fit together again. There are three holes in the PCB. I put the diode on the “back” and ran the leads through the holes at the top. Base assembled fine.
staze says
excellent! Yeah, mine I just soldered on the “top” of the board, and it went back together fine. I had some higher rated diodes, but figured why waste them! =)
Good to hear it’s working, and interesting that they may have had some lightning “issues”. Here’s hoping they continue to work. Mine has been working for about 2 weeks now since the new diode. Maybe next component order I’ll get a real surface mount diode to put on there…
Drew says
Seems to be a common problem, my other base until started acting up yesterday. Same indication ….. charging …. but phone actually slowly discarges. This time I wasted no time in bypassing the diode with a bit of wire (I got lots of bits of wire and to cheap to buy diodes) Phone back operational, so I’ll let ‘er go like that. As for the phones, if I remember correctly, I bought them a couple of years back from Future Shop. Weird that the diodes would go bad …. hate to think of all the other people out there having problems and spending money on either batteries or new phones.
Drew.
Bud Watts says
Thank you for posting this information! I bought an extra phone on Amazon back in January that I believe was a refurb. It worked fine until last month. I bought this for the basement, so when I went down there I would notice the yellow led on the top of the phone flashing. There was nothing on the display, it was dead. I brought it upstairs and put it on another charger and it charged up completely, no problem. I took the chargers apart, one good and one bad. They both had the same voltage. I checked the fuse and resistors and they were good, I decided that diode was bad but I really don’t understand why. Anyway I decided to bypass it and see if the phone charged which it did. I started looking for that diode on the web and I have come up with nothing. I decided to search google for ‘what diode in panasonic pnlc1029 charger’ and I came across your post. I am so glad other people are in this sick state of mind where they have to fix this stupid freaking phone. My wife said throw it away and I just can’t do that, I gotta make it work. I’m going to pick up a 1N4001 diode this week and put it in this dang thing and hopefully move on with life. As Drew said, ain’t the internet grand!
staze says
Thanks for sharing! Yes, it seems like Panasonic (or their OEM for the charger boards) skimped on the diodes… or got a batch of counterfeits. I’m also wondering if maybe the soldering job is just crap (lead free solder), and the jarring from dropping the phone back in the charger works loose the heaviest item on the board (the diode), which leads to bad joints, which leads to heating, failure, etc. The only charger that’s failed for me is the most frequently used one…
Joe Holdon says
So great to find the exact solution to one’s exact problem. Thank you for posting the fix!
Joe
wayne mitzen says
I think you may want to rethink this… here’s the issue
The 550mA NiMH bats in there – as with all rechargables – need to be charged in a particular fashion – see Cadex’s Bat University site. Typically with a constant current supply – this is why new Dell laptops use a one-wire to verify the correct charger is connected – with Lipo’s they can “vent with flame” if not charged correctly. Those “bricks” are a constant current supply that are set for the max “c” rate of charge for the packs
I think what Pana was trying to do was to make a constant current source out of a standard “constant voltage” supply. Hence the resistors.
I have a set of these phones – their charge management IC in the phone itself has issues. Actually – it sucks.
I currently (no pun) have one on a CC bench supply – totally eliminating the base charger. If I allow 200mA charge on any of the phones (some with new 850mA some with stock 550mA cells) the current will begin to pulse.
If I limit the charge to 120mA – it stays steady – the bench supply drops voltage and the current is limited to 120mA
If I open up the constant current to anything above 300mA the phone will only accept ~200mA steady, then after a few minutes the current will start to pulse.
See this vid – http://home.comcast.net/~ajawam1/panastupid.flv Note at about 40 second, even if I open the constant current up, it still stays at ~210mA
Here’s the thing see – http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride
Some highlights from this:
“Some advanced chargers apply an initial fast charge of 1C. When reaching a certain voltage threshold, a rest of a few minutes is added, allowing the battery to cool down. The charge continues at a lower current and applies further current reductions as the charge progresses. This scheme continues until the battery is fully charged. Known asthe “step-differential charge,” this method works well for all nickel-based batteries.”
Conclusion
BTW – 1C means to charge at the cell rating – in this case 550mA is 1C – That means that when the phone is almost dead it should be charging at a 1C rate – ie 550mA. According to Cadex it should:
“…The NDV in a NiMH charger must respond to a voltage drop of 5mV per cell. To assure reliable charging, NiMH chargers must include electronic filtering to compensate for noise and voltage fluctuations induced by the battery and the charger. Modern chargers achieve this by combining NDV, voltage plateau, delta temperature (dT/dt), temperature threshold and time-out timers into the full-charge detection algorithm. These “or-gates” utilize whatever comes first depending on battery condition. Many chargers include a 30-minute topping charge of 0.1C to add a few percentage points of extra charge.
Some advanced chargers apply an initial fast charge of 1C. When reaching a certain voltage threshold, a rest of a few minutes is added, allowing the battery to cool down. The charge continues at a lower current and applies further current reductions as the charge progresses. This scheme continues until the battery is fully charged. Known as the “step-differential charge,” this method works well for all nickel-based batteries.”
Note that with my bench supply I never see more than 212mA even with the constant current wide open
It appears that some “genius” at PANA misinterpreted the spec for charging a NiMH cell
See the vid – at about 1:30 you’ll see the “pulsing”…
– note from the cadex site:
“It is difficult, if not impossible, to slow-charge a NiMH battery. At a C‑rate of 0.1 to 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full-charge state accurately and the charger must depend on a timer. Harmful overcharge will occur if a fixed timer controls the charge. This is especially apparent when charging partially or fully charged batteries.”
Result – the batteries are not being conditioned correctly.
Dumbasses…
Conclusion 2 – by a new phone system that hopefully had someone that knew how rechargable batteries work….
staze says
Wayne,
Thanks for this. I’m not sure what you mean by re-think. But very good info. I haven’t had any issue since replacing that diode with a standard 1N4001, but it is very interesting. Looking at the circuit, theoretically, if they had put the diode in parallel with the resistors, that would create a 300mA constant current (0.6V diode drop in parallel with 2ohms), which is higher than you were saying created the oscillation on yours. But you COULD create a CC charger that way. The way it is, you’re right, I don’t know what they were thinking other than maybe some type of CC hack, or reducing the surge current when the phone is docked?
Panasonic SHOULD know what they’re doing, but like you, I’m not convinced they didn’t just farm this one out. But even that, they should have checked the circuit.
Funny how this post has gotten the most comments/hits of any of mine…
wayne mitzen says
Actually it’s not oscillations – it’s the charging routine they use for a NiMH… That pulsing is being controlled by the charging IC in the phone. And again – it doesn’t seem to jive with what Bat U/Cadex states is the correct way to charge a NiMH string. That 200mA doesn’t seem right for a 550mA cell string….
Tho here’s what I found – if you hit it the stock diode with freeze mist (or just take a can of air and turn it upside down), even if it’s working “correctly” ( I use that term loosely) – it stops charging.
Diodes like any semi are temperature variant. There’s a chart in this link/PDF:
http://www.kennethkuhn.com/students/ee351/diode_characteristics.pdf
Old audio amps I used to work on back in the 1970’s used a diode on the heatsink to vary bias on the output stage
So what I’m doing for now is using a Schottky SK-14 (digikey has them.) Tested it with a bit of heat and chill – seems to work OK. Recall a Schottky has a lower forward voltage drop than a GP diode like a 1N4xxx does…
This is probably why some have had temporary luck with what they thought was just a cold solder joint. The thermal shock may have changed the characteristics of the diode enough that the charge IC in the phone saw it’s threshold voltage.
I’m guessing the Charge IC will not do the step thing if the input voltage is a little off. What’s real weird is that when the voltage is off, and there’s only a few 100’s microamps flowing, the charge IC reports the on-board microcontroller that it should display “Charging” even if it isn’t
But the main thing is – it appears from experts like Cadex/Bat U that the batteries in these phones are NOT being charged conditioned correctly even when it works “as designed” .
Sad really…. I love the way the caller ID voice tries to pronounce weird caller ID’s… One spam call we get sounds like F*** U …
And as to “engineers” at Pana – I always recommend to a client needing a charging circuit to have someone like Cadex do it.
What I find is that most hobby shop products have some very sophisticated charging products as compared to what commercial stuff contains. Hobbiests like RC guys are usually tying to get the best charging performance. So those products have a fairly sophisticated clientele that won’t put up with shite like this… I’ve seen so many consumer products totally charge LiPO’s incorrectly. Some methods are actually quite dangerous.
wayne mitzen says
And I think the diode is just for blocking any reverse current should the 5.5VDC wall wart lose AC power.
Just a guess – I know we do that in stuff we design…
wayne mitzen says
Well – last post I promise – I figured maybe by measuring the current going between the charger and the phone might not give an accurate rate of charge on the cell string itself…
Yep – even lower charge rate – about 190mA steady, then after 1min 30 sec, it pulses at that charge rate…
I used a cool thing radio shack sells in a test lead kit – it’s two thin sheets of metal with an insulator sandwiched in between , with each sheet of metal tied to a probe socket (ie – you can stick a standard test probe into it)
It’s on the far right in this JPG:
http://powerreviews.s3.amazonaws.com/images_customers/08/87/28990408_213756_full.jpg
Manual for the lead kit:
http://www.radioshack.com/graphics/uc/rsk/Support/ProductManuals/2780039_PM_EN.pdf.
So when it’s disconnected from the charger I see about -20mA.
When I plug it into the charger I see 190mA then pulsing 190mA
When I unplug the charger I see about -100mA since the LCD backlight comes up.
So they are charging at 0.345C charge rate… I really don’t thing that’s quite right for the cell rating. As mentioned above that’s barely above what they state on Bat U:
“It is difficult, if not impossible, to slow-charge a NiMH battery. At a C‑rate of 0.1 to 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full-charge state accurately and the charger must depend on a timer. Harmful overcharge will occur if a fixed timer controls the charge. This is especially apparent when charging partially or fully charged batteries.”
staze says
Responding to all.
Yes, diode is there for reverse. Ah, makes sense about if the wall wart gets unplugged. Always just figured it was incase someone put in a ring positive connector. =)
Yes, I have that exact radio shack kit. Didn’t think about using it in this case, but good call. Makes me want to drain the batteries on the phone, and do a charging profile (voltage and current).
The pulsing of the charge controller makes sense. Makes me want to open one of the phones up and see what the controller is.
And yes, hobbyists tend to do better because they tend to be buried in the datasheets, and making it “right” rather than making it fast, which I’m sure is the case with these. It’s just weird Panasonic would do what they did. They’re generally considered one of the best major electronics manufacturers there is… but maybe they just don’t put a lot of effort into cordless phones (kind of a dying market).
Thanks again for all the comments. Just checked your CV, and wow, an Altium user. =) Also note your in a mother jones article. =) You spend any time on eevblog forums?
wayne mitzen says
Yea – been on his site before. The recent ramblings about how Altium’s move to china was reversed. Lots of speculation on that.
Been a user since Protel in the early 1990’s after Orcad tried releasing a windows version of what I had been using in DOS. Also dealt with PADS, I recall doing a few thousand parts for a guy named Dave Castine for their suite back in 1990.
Used to be that you did capture in Orcad, netlisted into PADS, exported to C&C for autoroute, then back to PADS.
As to the phones – One of the units i tested was totally dead – wouldn’t even fire up. No difference in the charge method – 200mA – steady for about a minute and a half, then pulsed as shown on the vid.
And sitting on my bench is another (I’ve fixed a lot of these) Pana DVD recorder thing. Those all have hideous power supply issues – they even sell rebuild kits on EBAY.
I was a bench tech for years back in the 1970’s and recall Pana being kinda OK. Not sure about now.
alex says
Thank you staze and others for sharing this information. Two of these chargers failed on me in the past month. I purchased the phones new from amazon around six months ago. I replaced the stock diode with the 1N4001 mentioned above and they are both working properly now.
Rich says
On mine, it took some swapping of parts before I could accept the fact that it was the base that didn’t work. I assumed the ac adapter would be bad or the phone itself, but not the base with just 2 resistors, a fuse and a diode. Mine would work for a while and then stop, then work again after a rest (cooling off). Fuses and resistors don’t do that and I had a 1 amp silicon diode. It seems to be working now. I still cannot figure out why there is a diode. Things would need to go terribly wrong for it to do anything. I wish I had found this before I wasted time swapping parts. If I had, I would have swapped out the diode as soon as I tested the voltage out of the ac adapter.
staze says
Yes, the diode is silly… but, I’m sure they had some reason (maybe they were taking up space in some warehouse).
And I did the same thing looking for the issue. Thought it was the wall wart, but swapped them and it still didn’t work. Then thought it was the phone. etc etc. Nothing in the base should break, but… here we are.
Thanks for the comment! Funny how this little post generates so much traffic! =)
James Pelletier says
Hi all:
I have the same issue. I should have no issue finding a replacement diode in the engineering lab. Can not get a datasheet on the M25 that seemed to match the size of the device anyway. My datecode was 1329 (29th week of 2013). I got the 4-pack phone option with the base. This is the only one (so far) to go bad.
All the solder joints look cold to me when looking at them under the microscope, All fuzzy and not smooth like they should be.
Thanks for all your input..
JP
staze says
Fascinating. Yeah, I’ve only had one die on me too, but it is the most used of the four. I’d be curious what diode you use to replace… I just used a through hole obviously, so the model of the SMD diode you replace it with would be good. I would imagine a 1A diode would be plenty… since we can’t find any info on the stock diode, I almost wonder if Panasonic cheaped out, and used something right at 200mA or maybe 250mA (given the model), but because of shitty soldering, or tolerance, they’re overheating.
Anyway, keep me (us) posted.
dtjohnson says
The surface mount replacement diode is apparently available at http://www.partsimple.com/ for 1.02. Shipping is 7.95.
staze says
ugh. Not worth it for that much, when a simple 1N4001 fit just fine. =)
owen says
So what was your final fix?
A bypass or the 1n4001
staze says
Owen,
My final fix was a 1n4001. Works great. Someone else in the thread just bypassed the diode… pretty sure that works just as well. Only point of the diode is either as a voltage drop, or for reverse polarity… we’re not quite sure. =/
James Pelletier says
Update:
Replaced the SMT Diode w/ 1N4004 through hole. Preformed it to fit the SMT footprint, solder it on, works just fine.
Before I replace it, I tried is a few more times…it Charged the phone for about 10 seconds until it got warm, then stopped charging…
Easy fix…(assuming you know which end of the soldering iron to hold… ;^) )
JP
Michael says
Hello,
My extra handset base charger have failed too,
Looking at the circuit board, there is two R1,
Do I replace both? If not, which one?
Thank you.
Perhaps someone could post a nice clear blown up close up picture of a fixed board.
Thank you again.
Staze have done good!
staze says
You want to replace D1 (the diode) not the resistors. I thought my update picture linked to the full size one, but it didn’t. Now it does!
Alan Eliasen says
Thanks for posting your research. 2 out of 6 of my chargers failed within a short amount of time. I thought that the batteries had gone bad, so I ordered more of them (and they didn’t do any better.) After seeing this page, I checked the voltage across the diode as it was charging, and found about a 2.9 V drop, and less than 3 V getting to the phone. The diode is almost certainly bad.
Panasonic doesn’t seem to sell replacements for the base. This absolutely appears to be a flawed design or a HUGE batch of bad parts.
staze says
Thanks! And yes, either that, or just a way-underspec’d diode (since we can’t find datasheets on it, who knows). Maybe someone with an SMU can characterize it. =D
That’s it! That’s the justification for buying an SMU, since this post has generated so much traffic. =D
Dennis says
First, I’d like to thank you for your post. Indeed “the internet is grand”.
After searching the net for a replacement charger for my Panasonic phone I stumbled upon your repair site. The thought of having to pay $30 for replacement for a two year old charger was more than I could take. So I went to radio shack and bought a pencil iron and a 1n4001 diode($13). I have never attempted any micro soldering before, so this was a new experience for me.
After the diode-ectomy was completed and the new one installed it seems to work perfectly. Charging as I write. I feel so elated for fixing something for a third of the price to a replacement.
Thank you so much again.
Dennis
Denis Halls says
A very informative string guys. I have a set of six KX-TG 856* series of Panasonic cordless phone made up of 4 pods and two main bases with one main base just acting as a pod. I recently had 7 weeks away from home where I switched all off at the wall except the main base as it is an answer phone. I did not remove the phones from the bases!
On return (two weeks ago) I have had an ongoing problem with two pods with exactly your described symptoms of showing charge but actually discharging and flat overnight. Now I know what to look for I’m pretty sure I’ll be able to fix them based on your research. Thanks so much.
staze says
Denis,
You’re very welcome! Interesting tidbit about not removing them from the base, but unplugging them…
Denis Halls says
Thanks Staze
Perhaps I should have mentioned that I did not turn the phones off on the handsets when I switched the wall power off so leaving them open to either natural discharge or drain through the suspect bases. Hind sight tells me I should have removed the handsets from the bases and switched them off on the keyboard which I will do in future when they won’t be used over an extended period.
Just waiting on the post for a pack of 1N4001’s and then I expect to have the complete set working again.
So pleased I found your site.
Denis Halls says
I should also advise that my base pods are PNLC1035’s but the circuit board appears to be the same for a number of the Panasonic phones . Certainly mine is identical to the one in your picture.
Denis Halls says
Update – just to advise that replacement of the diode in each of my two suspect base pods fixed the problem. Both pods fully charging the handsets now.
Only variation on soldering the diode in was that I didn’t bother to try to solder onto the original solder points as it was very tight so I stretched the diode between the input solder point and the spring contact solder point. This allowed me to keep the diode legs a little longer so I could heat sink them with a clip.
Again Staze – many thanks.
staze says
Very cool, thanks for the update!
And you’re very welcome! I can’t believe the amount of traffic this post gets. =)
Denis Halls says
Incidentally I don’t know what you are paying for 1N4001’s in the Staes but I bought a strip of 10 for 99pence – about $1.53.
Irvin Erler says
I was able to fix two bad chargers (I have 3 good ones) with the help about the diode. I have additional information. The voltage at the phone terminals with the phone charging was:
Good charger: 4.43 volts Bad charger: 4.35 volts. I placed a 1A diode in parallel with the diode on the bad board, and the voltage increased to 4.44 volts, same as a good charger. So, I soldered the diode in place. Problem fixed. I was surprised that this small difference was the problem.
staze says
Great to hear Irvin! I’m not sure it’s the voltage at the terminals, or if the diode is failing in such a way as to go open once some current is passing through it. I wish I had another one fail so I could use my programmable load (that I’ve gotten since my one failure) to see what is actually going on. =/ Ah well, still, great to hear so many people are getting these fixed!
daniel carlogiski says
Since the demise of Radio Shack, my access to parts is limited to the inter-web. What’s you opinion on just wiring around the diode>
Thanks
staze says
I think short term, you’d be fine. Longer term, I would just look at ordering some cheap-o diodes online (ebay from China/Thailand is always a decent option), then solder in a replacement once they show up. Since none of us have been able to figure out why the diode is even there, and they wouldn’t have put it there if they didn’t think it was needed, I wouldn’t just recommend bypassing it indefinitely.
I use this seller pretty regularly, shipping from Thailand is slow, but for $0.99, can’t argue (and it’s more than you’ll ever need). http://www.ebay.com/itm/25-x-1N4004-Diode-1A-400V-Free-Same-Day-Shipping-/260812095096
daniel carlogiski says
Thanks. I’ll brush up on long unused soldering skills. Luckily, I still have heat sinks from the ’70’s……
Rab Stevenson says
Thanks. Repaired a PNLC1035. It has the same circuit board TH165B inside it. Happy days. 🙂
staze says
Awesome! I love that this post is keeping so many of these chargers out garbage! =)
Barry C. says
Thanks! When I opened up the base, I also said WTF? 1 diode, 2 resistors & a fuse? This happened to me before & Panasonic sent me a replacement (in warranty). This time, I had an on-line chat. I described everything only for them to say – out of warranty – call this 800 number. Rather than pay $12 plus freight, I did a search & found this posting. I also did component checks – resistance & voltages, so also suspected the diode. I’have also heard that lead free is less reliable than traditional lead-tin solder. I put a dab of rosin on the solder joints and reflowed them. So far so good… If this doesn’t work, I’ll put in a 1N4001 or equivalent.
Barry C. says
One more thing. Panasonic doesn’t seem to be interested in fixing this problem. Even if these things are made in China, it would appear that they are using a wave soldering machine to assemble these circuit boards. Well, they wouldn’t do these manually, would they?
staze says
No, they wouldn’t do it manually. Judging by the color/texture of the solder in mine, these are reflowed. So parts are placed in solder paste, then that is placed in an oven, and the paste is melted/flowed. And yeah, lead free solder sucks. Sadly, it’s all anyone uses anymore (save the US Military and NASA, from what I have read).
Still, it does seem odd that Panasonic hasn’t addressed this issue with later versions of the charger. But, I guess if they aren’t replacing a ton of them in warranty, then what do they care?
John Busser says
Just a note for others. I had two bases that failed and replaced two diodes, One worked and the other did not. The orientation of the diode is important.
Understand how a diode functions. A diode is composed of an N-type semiconductor joined with a P-type semiconductor. The N-type semiconductor is the negative end of the diode, and is called the “cathode”. The P-type semiconductor is the positive end of the diode, and is called the “anode”. •If the positive side of a voltage source is connected to the positive end of the diode (the anode), and the negative side is connected to the negative end of the diode (the cathode), the diode will conduct current.
•If the diode is reversed, the current is blocked (up to a limit).
Rich Koselow says
For your info, base is available at Panasonic website for $11.99 with free shipping.
It is an updated version with a ZB suffix.
gredit says
Googled across this today, trying to fix my charger. Dug into my parts stash and found a 1N4001 from about 35 years ago, fired up the soldering iron — back in business. Made me very nostalgic — thanks!
staze says
Glad it worked, Thanks for the post!
Charlie F. says
I own a Panasonic phone system with 4 of the PNLC-1029 chargers that is about two years old. One phone started to have charging problems. By the process of elimination I eliminated the phone and the charging cable and was about to buy a new charger when I found this article. So I took the charger apart and re-soldered all the solder connections I saw on the card and that solved my problem. I made sure I did’t use an iron with too much heat, just enough to cause some new solder to flow onto the existing solder joints.
staze says
Awesome, let us know how it works. I found reflowing the solder only fixed the issue for a week or so. I had to actually replace the diode to get the problem fixed long term. =/
Tom says
After almost two years of messing around with four apparently defective Panasonic phone chargers (PNLC1029) I began internet surfing for solutions one last time. I came across your blog and, much to my delight, I found the fix I was looking for.
By the way, the problem you encountered with your charger was exactly what I was dealing with i.e. handset batteries would not charge and eventually would go flat. Much like what others did I tried multiple brands of replacement batteries, called Panasonic, read and tried various base station/handset reset procedures all to no avail.
Off to Radio Shack I went this morning where I found the 14N001 diodes in stock for $0.79 apiece. I got back home and replaced the suspect diode in one failed charger and voila! things appeared back to normal with the charger. I proceeded to replace the diode in each of the remaining three. It appears that all four chargers are now charging the handset batteries, Time will tell if the fix is good but I suspect that indeed it is.
Thank you for taking the time to analyze and fix the problem. More importantly, thank you for posting your work so that others might benefit.
Have a great day.
Tom
Tom says
BTW, since replacing the diodes yesterday all of the chargers have charged the handset each of which now displays Fully Charged. It’s great to have this thing solved. Have a great day. Tom
staze says
Hi Tom,
Thanks very much for your note! I’m glad it worked!
I’m starting to think that the diode is being “blown” when the phone is left in the charger, but the charger isn’t plugged in… but I haven’t tested this yet. =/
Thanks!
greg says
I have the same problem I replaced my batt and still no fix and started looking for a charger when I ran across this post and to let you know my phone has always been in the charger with power to it I have never killed the power to the charger so tomorrow I’m going to run out to radio shack and pick me up a diode and hopefully that fixes it thx for the posting
greg
staze says
Great to hear! Let us know how the repair goes!
greg says
well went to radioshack to pick up a 1n4001 website said they had 4 instock but had none so I went to order it online and come to find out it is 149 plus 599 shipping and handling I’m not paying that for s&h I see were you sent or posted a place to get one but however it is a 1N4004 Diode will that work as well as the radioshack here in Oklahoma city does carry that one in stock thanks for all your time and info in this matter
thx
greg
staze says
ugh. So, what timeframe are you on? You could order some from China (ebay) on a slow boat, or heck, I could probably mail you some myself (I have tons of diodes). How’s your soldering skill if I mailed you some actual surface mount ones?
If you’d like to take that route, shoot me your address via my contact form. I can’t promise I’ll get them out quickly, but it should work. =)
greg says
hello thx my soldering skills are pretty good I’m not new to that use to work on pagers for about 15 years lol back in the day ill take and give you a email with all the info and once again thx
Ray says
I had a set of four. One stopped charging for a couple of months ago, and I followed the advice here to replenish the solder on the diode; it works fine so far.
This week the second one died. While trying to do the same, surface mount diode came out. While trying to put it back, the copper channel peeled off. I added wire extensions to the ends. The problem persisted. I saw another crack/peeling on another channel, too. The quality of the PCB is terrible and I don’t have the patiance.
A new replacement base costs around $13-$15. There is no guarantee it (they) will not come with the same issue. Not worthed to try.
I cut the whole circuit (PCB) out, and soldered a surplus cell phone charger (5.5V 800mA) I had at home to the wire posts the handset is sitting on. So far, it is charging fine. If you don’t have one at home, you can buy one for a fraction of the original.
800mA is a bit higher than the original spec (500 mA), but I’ll take the risk (a new AAA rechargeable battery still costs much less). If it dies early, I’ll put one with a higher recharging current.
Don’t forget to peel off the original label at the bottom of the base, as it is no more valid.
Russell says
Thanks so much for the info. Less than $1/each for the diodes and I have two phone chargers that are now working again! Thanks again…..
Russell says
@greg, you can get 5 of the 1N4001 on Amazon for around $5 with free Prime shipping.
Gerard Tynan says
Thanks for this post, I had 3 chargers that failed, all working again. Brilliant.
SteveP says
Isolated mine to the base by swapping parts: batteries, phones, AC unit and base. I had initially thought it was the batteries and had already replaced those, Had several 1n4001, so cut out the diode and replaced with mine. Had the diode leads bent tight and diode angled over to the charging contacts, no problem putting unit back together. A little piece of tape held the diode in place to solder. Seems to be working again. Will update. If this is now fixed, thanks a ton for the diagnosis and fix!
Ray says
Follow-up: It has been a month, I am testing my new charger, and it seems fine. No heating of the batteries at all. It was a Nokia cellphone charger I used, and it is known to be a quality product, so the problem is solved to last. You can get one of these chargers from surplus stores for $2-$3, or for 50 cents in a garage sale. Saves time and money.
staze says
Should be fixed! Thanks very much for the post!
VNAZ says
Thanks for the post. One of mine began this behavior and I I did like several did, the try other changer, other batteries, other handset… Then did the Internet search and this post popped first. BINGO! I have taken the resolder route first, but have the common diode Staze used on hand if I have to go back it. In the mean time fully operational at this time.
staze says
Awesome, thanks so much for the post! Can’t believe how much traffic this post gets… and how crappy these chargers were. =/
Bill says
I’m thinking the diode is there to control the charging voltage to keep the batteries from being over charged. When the voltage on the input and output side of the diode(just to keep it simple) is equal then the diode will stop conducting and thus stop charging the batteries. If this is why the diode is there then it will not be a good idea to straight wire across the diode.
Bill Gibbs says
I have a Panasonic battery charger model PQLV30053ZAS for a Panasonic cordless phone model KX-TGA101. The charger circuit board only has 4 low ohm resistors which have leads instead of being surface mount leadless resistors. On the circuit board of the charger is the date 2005-12-25. It uses the same model AC adapter as the PNLC1029. On my PNLC1029 charger circuit board is the date 2011-11-16. Apparently later Panasonic decided to eliminate two resistors and add a diode to give better control of the charging voltage. In my opinion the diode will better prevent overcharge of the two NI-MH batteries. I would appreciate some input if you find this little bit of info interesting.
KeeganG says
Much like everyone else in this thread,I too ran into the same problem with the charger not working. Initially, I figured the phone’s batteries must have been old so I replaced them, only to run into the same issue. And then I found this page…
Following the instructions, I removed the diode and replaced it with a 1N4002 I had lying around. Still wouldn’t charge though. Luckily, after reaching out to staze he pointed out that I had soldered the diode backwards. I corrected this issue and now I have a fully functional charger. My phone is fully charged as I write this!
Thanks staze!
Greg says
Just wanted to add my name to the growing list of grateful people who found your information on the web. I was about to buy a new charging base but have now replaced the diode and everything is working perfectly again. Thanks very much for posting this solution so that we can all benefit!
Marko says
One more person who founds this post extremely useful. Thanks!!!!
Jeremy Maccelari says
And another thanks! I was looking at replacing a non-functioning PNLC1035 for around £23 (a new phone is only £29!) when I found this post. A whole 9p for a 1N4001G at Maplin later and it’s working perfectly again!
Beverlee Teifer says
We had the same problem and I saved this post for my boyfriend to read as I didn’t understand most of it. He got the diodes and all of our chargers have been fixed for months now! Thank you! Thank you! Thank you!
Mark says
I just want to thank you for this post! I had one charging base fail within a month or two of purchase, and then a second one this weekend (of four bases). I bought six diodes, and replaced/repaired the two defective ones. Both bases are charging as expected now; if they fail from here, it is because of my shoddy soldering skills. Because I bought extra diodes, there shouldn’t be any more failures. 🙂
Vic Main says
Thanks for the info, my charger needed a new diode too. I soldered mine to the cradle connector on one end and the pad for the original diode on the other, it lays flat that way, and doesn’t look too bad. I’m sure the original diode isn’t a zener, but a normal one used so that the batteries don’t drain through the charger.
Thanks again!!
Vic
Frank says
I bought 10 pack of 1N4001 at Sayal Electronics in Markham (Toronto), ON for just $1!
Soldered in the new diode, band of left side as per |<– marking on circuit board.
Voila…charger working again. Saved myself $20 for a replacement charger on eBay. And I have spare diodes to fix the other 2 chargers in my set of phones just in case they fail in the future.
Thanks!
staze says
Awesome, thanks for the post!
Denis Halls says
Staze,
Just thought I’d update you from my repairs in April/May 2015. The system is still going strong. No more problems with any of my four PNLC1035 pods.
This was or still is a great string and so helpful to so many people.
Well done & thanks.
Denis.
staze says
Awesome news, thanks!
Denis Halls says
Just to add, as I said when I first did this repair, when I go away (holiday etc) I still turn off the pods (6) at the wall mains power outlet then turn off the handsets on the red close button. Every time I return and switch on the handsets all still show full charge, even after a 12 week period away.
Denis Halls says
Six handsets includes two fitted in base units, one used as a pod. As we know the base units have never had the same problem.
Guido says
I want to thank you for posting this FIX.
It was the diode, too much drop across it.
Replaced the diode. Phone charges! Yes!
Thanks!
FrankC says
FrankC
Thanks for the tip…I have two of these handsets and, like others, swapped components until I was satisfied that the base was the problem. Then I saw this blog and replaced the diode with a 1n4004..seems to work perfectly. Using a kill-o-watt i saw a 20ma current draw both on the repaired base and on my other working base…no difference. Although the resolution on the kill-o-watt is only 10ma so there could be roughly a 5ma difference that might not show. In any case, I am comfortable that all is good.
OBAFGKM says
One our sets had the same problem. Wife was about to drop phone, base, and adaptor in the trash before I stayed her hand. After confirming the problem lay in the base, I found a replacement on EBay for $30 + shipping. I was appalled. Then I stumbled across this excellent thread.
Poking around, I found 0.6v across the diode, but zero across the spring phone terminals. More poking confirmed an open circuit between the diode’s solder joint and the adjoining phone terminal. Then, after more poking to make sure I hadn’t done something stupid, I found 6v across the phone terminals? The damned thing had healed itself! Apparently, that solder joint is indeed “loose,” and the prodding had jostled it back into a conductive state. The phone currently says it’s charging (it was stone cold dead before), so I’m going to let it continue and see how it goes. I think I’ll also try resoldering as recommended above. Just hope that doesn’t break something.
staze says
Great to hear! I will say, I did this “fix” a few times myself, and it resulted in it just breaking again until I replaced the diode. Hopefully just reflowing works for you!
OBAFGKM says
The junction opened again after a few hours. I reflowed the junctions at the phone terminal and on each side of the diode, and so far, so good a week after. Wife is impressed. (I hope it holds!)
Denis says
I only wish that I’d found your site before spending hours repeating what others had already done. My only contribution would be to confirm that the offending component is a 1N4002 type rectifier made by Kexin who mark it “M2”.
Jeff says
OMG! Thanks to all for posting! It was so much more interesting reading this thread than the usual drivel I see on internet blogs. I’m an EE (digital), but all the comments so much reminded me of my early education and hobbyist days. Kudos to the guy whose wife told him to throw it out, but he couldn’t NOT fix it! Wayne Mitzen: thanks for all the research, and staze: thanks for starting the post and your repeated updates! A round of applause to all you EEs, techs, hobbyists, and DIY’ers!
Jeff says
Oh, BTW, my phone charger base also malfunctioned. That’s why I’m here.
staze says
you’re very welcome! I’m glad this post has helped so many people. =)
Matthew says
I also fixed my base with the same problem. Got 10 1N4001 diodes from ebay for $1.58 with free shipping. A few minutes later and the base is working. And now I have extra diodes if the others fail. I would also suggest this nifty tool from Harbor Freight for help in holding everything and seeing while soldering.
https://www.harborfreight.com/helping-hands-60501.html
Thanks for the fix!
Avi says
hello
Since orig diode is M2S, I believe it is possible to replace the SMD diode with M2 replacement diode which is equivalent to IN4002.
M2 SMD diodes can be found on eBay/AliExpress for ~1$/50pcs
Have fun
Avi
Richard says
Hi Staze, and everyone.
I’m a newbie to your site. I’ve been reading the posts with fascination as I too have concluded (over a year ago) that I have a bad PNLC1029 charger. Like several others, I was amazed it was that stupid little thing — as determined by swapping chargers — instead of the phone or the batteries at fault.
I may have stumbled onto an alternate solution *for myself* — it’s not likely to help anyone else. But I have a question for you apparently-knowledgeable electronics enthusiasts. I recently dug another charger out of a box of junk someone was throwing away. It’s a Panasonic PNLC1010, and has the same form factor as the 1029. The only difference I can find is that it puts out 6.5 volts instead of the 1029’s 5.5.
I’d sure appreciate some feedback as to whether or not this would work without frying some component of my phone or shortening the battery’s life. (I tried to find charging specs for the HHR-55AAABU battery but wasn’t successful.)
Barring that easy swap, I think I’ll try what appears to work for several of you: short circuiting across the diode.
Thanks so much for this post, Staze. I can tell you must have been blown away by the amount of attention it’s received. Many of us are grateful for its existence. I’m still irritated at Panasonic when I think of how their rep. casually told me the solution to my problem with this relatively-new phone was to send them another bunch of money to get another charger! Grrrrr.
I used to assemble printed circuit boards for a small electronics firm. But I no longer have a workbench or the sharp eyesight I had, and possibly not the patience to locate and install a replacement diode — we’ll see, that could change. But I’d like to go the easy route first. 🙂
Avi says
@Richard
I would not recommend using a 6.5VDC adapter/charger on a 5.5VDC system.
It might damage your equipment.
Better get a replacement PNLC1029
BTW, for anyone interesting in a possible fix for PNLC1010, looking at its service manual, it does NOT have any diode! Its only components are a fuse and a resistor, so this page fix is not relevant to it.
Mike says
Had 2 of my 3 charging units pack up on me.
Like others, I changed the power supply and the phone’s batteries with no luck. Had looked inside and thought: well that’s so simple – how can it go wrong.
Just ordered a strip of 10x 1N4001 diodes from eBay for the princely sum of £0.99 (GBP) with free delivery.
It will be very pleasing when they work again!
Many thanks all!
Mike says
Just an update…
I replaced the diodes in all 3 base units without much difficulty, and they have all working perfectly fine now for a few weeks.
A most excellent result indeed. 🙂
Greg R says
Amazing! I found your site just by searching for “1329 M2S diode” when my PLNC1029 charger failed. I had the same symptoms so I thought,must be cold solder but the voltage drop was still 1.0V on the diode leads. I pulled it and then it measured .7V. How bizzare! New diode fixed it
Thanks!
Larry says
Amazing, thank you folks. I have an older Panasonic DECT, 2007, it’s been doing the same thing as all of yours! Like everyone else I tried the “obvious” fixes first then took the base apart and thought there’s nothing to go wrong except contact resistance for the drop in handset” . After cleaning, to no avail, I too measured the diode drop and decided look to see if anyone had info on it and here you all are. I opened a later handset base and that had no diode, the little PC board is identical but the diode’s contact points have been shorted by PC track; oh and the 10ohm axial resistor is raised to 12ohm. Excellent site.
Phil says
I’m also a victim, started doing the swapping thing, thought I was going crazy there for a minute until I found this blog. Once again, thank you Staz for starting it. Truly amazing how much traffic it’s gotten. Also thanks to ‘Russell’ for the Amazon source for the diodes.
Bob says
Awesome. Found your site, grabbed some 1N4001’s, fixed my base. Thank you!
Rick says
Same problem here. Thanks for the great series of posts. Initially I assumed it was the power brick but swapped it with another base. Charging problem stayed with the base. I just ordered some 1N4001 diodes from Amazon. Thanks again!
Bob says
June 7, 2020 my PNLC1029 charger also failing to charge phone and stumbled onto your info which I followed after finding that I did have a 1N4001 and soldered it in replacing what ever was the one that was in there. Testing it now and hoping it will fix my phone charging troubles.
Thank you for posting your info.
Bob says
Panasonic 6.0 Plus Phones with what was a very troubled PNLC1029 charger.
The fix seems to be working.
The numbers of the failed diode, the best i was able to read: 1241 1R0
Thank you again !
Bob 3D Printing
staze says
Awesome, glad this helped. Good luck!
staze says
1241 1R0 would be a 1ohm resistor made in the 41st week of 2012. There are two of them in series in my chargers.
My diode was also marked 1241, but the other marking was M25.
Dwayne Gitter says
I used a IN4007. So far it is working.
Thank you all!
Don says
I had the same charging issue. Read this article, bought a diode ($0.50), trimmed and soldered it in, an VOILA – all working again. Thanks for the article, it really helped.