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Old 14th January 2012, 03:34 PM   #81
RJM1 is offline RJM1  United States
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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.
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Old 13th March 2012, 03:36 AM   #82
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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.

G
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Old 13th March 2012, 03:54 AM   #83
benb is offline benb  United States
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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
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Old 13th March 2012, 04:11 AM   #84
scott17 is offline scott17  United States
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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.
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Old 13th March 2012, 04:40 AM   #85
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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.
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Old 13th March 2012, 05:01 AM   #86
scott17 is offline scott17  United States
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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.

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Originally Posted by scitizen17 View Post
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.
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Old 26th July 2012, 01:01 AM   #87
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Good thread, and while most of these great anecdotes are way out of my league, if you don't mind, I'll share a second-hand one, albeit not audio-related (and perhaps apocryphal).

Years ago, a colleague of mine was doing tech support, including for a terminal/green screen-type application. Numerous fields were presented, into which various codes were to be entered. A user called the helpdesk and complained that the focus would jump from field to field 'by itself', rendering her job impossible.

He went to her desk, sat down, and could find nothing wrong; her colleagues were unaffected by the 'bug'.

After a while exploring various avenues to no avail, he asked her to sit down and demonstrate when the problem occured, and then it dawned... Either TAB or SPACE could be used to switch focus. The lady in question was both slightly short-sighted, and generously proportioned.

As she leant forwards to squint at the screen, her ample breasts pushed against the space bar...

I don't recall precisely the wording he used when closing the ticket.
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Old 26th July 2012, 04:52 AM   #88
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An old B/W TV was sometimes not turning on. I knew there was an open circuit somewhere but couldn't fix it after soldering lot of places. Then I got an idea to locate it. Just made the room totally dark in the night and then the open circuit showed itself as sparking. The wire on the fuse holder was the culprit.

Gajanan Phadte
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Old 26th July 2012, 10:25 AM   #89
M Gregg is offline M Gregg  United Kingdom
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Regards strange repairs..

Looking back at a regonda HiFi in the seventies (I was 15)..One channel not working.

Opened it up and we could see a burnt mess on one side of the board didn't know what it was so we went to a local repair shop and the "nice man" gave us a copy of the circuit. After going home and reading the drawing it was a 1 Ohm power resistor that looked like a coil of wire..My friend said where we going to get one of those?...I said don't know we could repair it..have you got any wire..its got to be higher resistance than copper...

What about my guitar? here have the High "E" string...it was a pig to solder.

Power on and it worked fine and was working 5 years later..

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M. Gregg
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Old 26th July 2012, 10:38 AM   #90
M Gregg is offline M Gregg  United Kingdom
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Here is another..

Whilst working on some PLC automated equipment (in the late 80's)..We kept getting IO control cards going faulty...we changed them and the next card would fail...

So after a few months we got one of the cards and looked at it under a microscope..The opto coupler chips had what looked like pencil lead between the legs.
So we waited for a shut down and took all the IO cards back to the lab. Guess what they were all the same with this pencil lead type growth across the legs, however only on the opto couplers.

We tried ultrasonic cleaning and coating with lacquer..guess what, it happened again and eat through the lacquer. We contacted the manufacturer Honeywell..and they changed the chip type..No more problems.

I guess I should add the growth looked like it had been plated onto the plastic package of the chip..Shiny black with the shine you get from oil on water..

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M. Gregg
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Last edited by M Gregg; 26th July 2012 at 11:07 AM.
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