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Midland 75-785 Handheld CB Repair

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Midland 75-785I recently picked up a Midland 75-785 handheld CB at Goodwill for $6, and thought I would see how it worked. I’ve thought several times about taking the HAM exam, and figured I might want to start out using a CB, repairing a CB, etc. I got the unit home, and fired it up, and it seemed to work okay with a simple 50R rubber duck antenna I got off my scanner. One thing that didn’t seem to work, however, was the battery charging circuit. I had some older Ni-Cad batteries to try in the unit, but they would quickly drain, and worse, the charging circuit didn’t seem to work (plugging it into my bench power supply, it would draw about 150mA at 13.8V, then quickly ramp down to 10mA, and sit there. Never really charging.

So, being one to never throw something out without first trying to fix it, I took the thing apart! Which consisted of 4 screws on the back piece, then another screw hidden under a battery spring on the remaining battery holder. Taking the board out is a bit challenging, but nothing is holding it in, you just have to work it past the case.

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HP 5316a Repair

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5316AOnce again, knowing no end to repairing things, I saw an HP 5316a come up on eBay for cheap ($20), that I bid on first thing, and ended up winning. Not sure I WANTED to win it, but hey, it’s a repair, I’m cool with doing those. Maybe I’ll be able to resell it, maybe not. *shrug*

3 days later, it showed up on my doorstep via FedEx, and looked to be in good condition, except the missing handle and feet, as described by the seller. Initial power up showed it power up okay, but never register any count. The gate LED would trigger, as would the sensitivity LED, and both could be adjusted. I did get a alternating flashing of the HP-IB LEDs on the front panel though (at this time, I didn’t know what this meant).

After opening the unit, I noticed two empty sockets, one on the HP-IB (GPIB) card, and one on the main board. It appeared they were used for a ribbon cable between the two, but the cable was missing. Also, another power up showed an E2 error (which translates into a failed HP-IB card)… which isn’t surprising given the connection to the HP-IB card was missing. I’m just not sure why it booted okay previous to that.

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Ampeg B-80N Repair

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Ampeg_Jet-70My dad recently dropped off his guitar amp, an Ampeg B-80N from the late 70’s or early 80’s, for repair saying that it wasn’t working. It was behaving oddly, then just stopped working one day. Figuring it should be easy to fix, I gladly said I would take a look. First thing was obviously pulling it apart and seeing if anything obvious was wrong. The trick to taking these apart is to remove the speaker grill, then the 9 screws that hold the speaker on, drop it down and unplug the spade connectors on the driver. Then unscrew the amp on the back, and pull it straight off, and then pull the speaker wire out of the hole that it threads through down to the sound box. Make sure to note which lug plugs into which spade on the speaker, btw. I just snapped a quick picture with my phone.

Anyway, pulling the amp, there was nothing obvious wrong other than being a rather old design of a, I believe, class AB amp. It uses a diode pair (STV4H) to bias the output transistors, and unfortunately, that diode pair is at this point, unobtanium unless you want to spend $60 on ebay.

Okay, anywho, after the initial look, I contacted Ampeg (or rather, loudtechinc) to get the schematics, and manual for the amp. Sadly, they don’t post schematics on their site like Fender, but if you contact them, you can ask, and they’ll send you back an indemnity clause that you agree to not electrocute yourself, then they’ll send you the info. Took about 2 business days to get the schematics ((btw, I find these old schematics funny given they use the old symbol for polarized capacitors)).

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