A friend recently purchased a Pioneer VSX-452 Receiver at Goodwill for $15 without being able to listen to it fully. After taking it home, and hooking up some headphones, and speakers, he noticed the left channel sounded terrible, where the right sounded fine. He mentioned this to me the next day, and I figured “hey, I can fix that”. Especially after just reading a pretty decent book called How to Diagnose and Fix Everything Electronic. Anyway, I took the unit home, and set about diagnosing it.
Dell E173FPb Repair (BenQ)
I recently repaired a Dell E173FPb monitor from my wife’s work that would just start up black, with no “2 seconds to black” or anything like that. The common issue with these monitors is the backlight transistors on the power supply shorting. When I got the monitor, I pulled them, and indeed, a pair of them were shorted out, so I ordered some replacements through a pretty highly rated, Chinese, eBay seller. After receiving them, I dropped them in, and it STILL didn’t work. So, I ordered replacement FETs (since testing FETs is a bit troublesome at times), and those didn’t work either. Awesome… so I put the original FETs back, and set the monitor aside for parts.
A month later, I was ordering some parts from Mouser, and noticed they had the transistors that this monitor used, so I ordered a half dozen, to see if maybe they would work. After receiving them, I dropped them in, and viola, it worked!
So, it short, buy from real component retailers if you can, and avoid getting cheap counterfeit parts. You’ll save yourself a headache or two.
And here are some links to articles dealing with repairing this monitor.
http://www.badcaps.net/forum/printthread.php?t=6692
http://www.badcaps.net/forum/showthread.php?t=20295
http://www.badcaps.net/forum/printthread.php?t=9600
http://homepage3.nifty.com/anikikobo/hardware/benq_fp71g.html
http://www.badcaps.net/forum/showthread.php?t=14068
http://www.badcaps.net/forum/showthread.php?t=7649
http://www.badcaps.net/forum/showthread.php?t=12432
http://syscon.wordpress.com/2007/07/13/dell-dell-e172fpb-lcd-backlight-repair/
http://www.badcaps.net/forum/showthread.php?t=20295
http://www.ccl-la.com/LCDrepair5.htm
Keithley 197 Repair
Given my experience, and eventual success in repairing my now indispensable Keithley 199 Multimeter, I recently picked up a non-functional Keithley 197 Microvolt multimeter on eBay for $25. Vintage is about the same for this model and the 199, and after looking at the manual (which includes schematics), I figured it was worth the $25 to give it a go at repair. Best case, it was easy and I could turn around and sell it, or give it to a friend.
The unit arrived in relatively short order, and indeed, in all settings, the meter just read “OL”. So, first thing that told me is, processor is working. EEPROM too, more than likely. So, going by the manual, and logic, I started with the voltage rails. The 197 has a few. Basically a ±15V rails, a +10V, a +5V analog, a +5V digital, a -6.4V, and a +2V reference. All of these are regulated by diodes rather than more modern LM78xx/79xx regulators. So, going through the checklist, it soon turned up that the -15V (-V) rail was dead. At first I thought diode, but testing the diode out of circuit resulted in a working diode. So something was pulling that rail up toward ground. So, trace time.