Strangest electronics repairs

[RJM1]

One strange one that I remember from about 1980. I was working on a Kenwood High Speed DC reviver it had one blown channel. Outputs blown, drivers blown, VAS, tone control transistors. This unit had a microphone input which had shorted and blown every stage all the way through the outputs. Boy, I hated working on them.

[stratus46]

Had another one just last week in a Sony Digital BetaCam DVW-A500 which would not play the old analog tapes. After replacing all the 'lytic caps, most of which had bled acid all over the place it still was sick. I found a pair of traces the acid ate through requiring some kynar wire to reconnect. The last failure on that board was a 620 ohm SMD resistor that the acid destroyed. I read it as open with a meter and when it gave the awful 'fish' smell during removal I knew it would be good again.

Another identical board a few days later had a -5 Volt supply reading +7.2 with the new caps on that leg bulging because THEY were reverse polarized. I could find no components on the schematic connecting these supplies but read a 1.4 ohm short between the supplies. I found a -5 trace on top of the board very near the +7.5 and after removing the new caps found I didn't do a good enough job cleaning the acid there. More careful cleaning cleared the short but one of the chips on the -5 buss didn't survive the +7.5. Fortunately the machine is 'new' (20 year old design) enough that the chips are still available.

G²

[benb]

strautus46's post of bad electrolytics reminds me: The local robot club had an "oscilloscope seminar" where I heard about the Tek TDS scopes being victim of the "capacitor plague" that attacked so many PC motherboards and power supplies in the last decade or so (there's a thread around here about it a year or two ago). The guy (who runs a very successful business unrelated to scope repair) told how he bought several of those "broken" scopes off of ebay, repaired them and sold most of them at a nice profit.

I just googled Tek TDS capacitors and found this, an apparently related problem that developed LONG AFTER the bad caps were replaced:
SV8YM: The Leaking Electrolytic Capacitor Plague and my Tek TDS-460

[scott17]

Used to repair the NV-8030 (along with vidicon cameras and such) back around '79-81. Not strange, just outright wrong! These are not fun.

Scenario: Gas station/convenience store in the middle-of-nowhere Georgia. Shiny new surveillance system. The guy couldn't figure out why his new time-lapse recorder was not working as it sat there next to a bacon grease filled frying pan! Just one of many.

[Bibliophile]

Another in the "not strange, just wrong" category.
Years ago I worked at a video distribution plant where hundreds of VHS and a lesser number of Betamax cassettes were duplicated from one inch C format masters.
One of the Sony extended reel playback machines (I think they were BVH1180PS) would not reliably play some masters. On inspection, I found that after years of use, a groove had been worn in the takeup side capstan shaft. Some tapes were marginally thicker than the groove depth and would play. Thinner tapes would not (we are talking microns here).
Management would not come at the price of a replacement capstan motor so I spent hours holding a piece of abrasive paper wrapped around the shaft to grind it back to a uniform thickness. Of course this slightly altered the playback speed but luckily it was still within the the servo locking range.
This resulted in me later been fired from the job because when management looked at the service records, they found that I had recommended that the motor be replaced some months previously. This put the chief engineer in an embarrasing position and he was gunning for me after that.

[scott17]

Not to expand too much further on this particular topic, but when the front loading time-lapse cassette recorders came out, guess where the electric frying pan was now? Yep, right on top. If I remember correctly, I think that particular store burned to the ground.

Originally Posted by scitizen17

Used to repair the NV-8030 (along with vidicon cameras and such) back around '79-81. Not strange, just outright wrong! These are not fun.

Scenario: Gas station/convenience store in the middle-of-nowhere Georgia. Shiny new surveillance system. The guy couldn't figure out why his new time-lapse recorder was not working as it sat there next to a bacon grease filled frying pan! Just one of many.