26-04-2012, 03:42 PM
We used to call them something else...reverse the lock & fit and sub another word for fit.
The subject of transistor problems has taken me back to my days with Sony in Canada.
Back in the seventies at Sony we were starting to get stuff in with various faults but a lot of them seemed to have a familiar "ring" to them, most commonly intermittant problems (the worst) across all types eg: amps, tape decks, tv's etc, some of these were real nasties ie: iintermittant only once in the w/shop...send back out...bounced a few weeks later.
Typically (but not always) the symptoms would be intermittant crackling or noise (like resistor noise) in audio products or intermittant video/IF/chroma problems (colour tv's) it was giving us a real headache.
First approach was the normal one, intermittant = dry joints, out come the blunt end of screwdriver and a knitting needle, bang bang tap tap till your in the area, inevitablely it was the print side of a transistor connection, got to be a dry joint then, out comes the bench magnifier...looks ok but I will resolder the three leads anyway...stick on soak (sometimes for a fortnight) it's fine, send back, next week it bounces...sod it, same proceedure again only find it on a different transistor, same fix, same soak same bounce.
Ok time to nail this little b*****d had a real good luck and a re think as we were now getting a lot of stuff coming in with weired faults and the boss is getting concerned about the back log, normally I'm on the fault within half an hour at most, this was getting to me, anyway as said had a re think, maybe the transistors are responding to taping due to a problem with the transistors internall connections, takes transistor out and checks it, all ok. Eventually a tape deck came in that was intermittant noisy on audio and the intermittant problem stayed long enough for me to find what was causing this problem with the transistors used in most of the Sony products, it responded to the usual taping etc, again narrowed it down to the area of a transistor, wiggles the top of the transistor and the fault aggrevates, must be a dry joint or an internal failure, it was neither of those things although the transistor was to blame, I removed it and had a real close look under the bench magnifier at the base of the transistor (the underside) and there radiating out and under a certain light was flourescence looking deposit (looked like what petrol on water would look like) it radiated out from the center lead (I think that was the collector) and had spread to the other leads and it was conductive, so taping the PC board was enough to cause this conductive connection to become none conductive due to the vibration caused by tapping or wiggling the top of the transistor, the act of removing the suspect with a soldering iron also broke that conductive link but given time, usually a couple of weeks, it would be back to its old tricks again. From that day on finding these nasty intermittant faults caused by the above became a breeze, just slighty stroke or wiggle the top of the transistors and it soon became clear which one was at fault.
When I eventually returned to the UK I needed work so I got a job as a bench tech with a local Radio & TV firm, most of the techs were only used to the usual Thorn, Phillips,ITT stuff, they asked what my favourite stuff was and I told them Sony or other Jap stuff..."Right then you can repair the bl***y lot" which was fine by me as I knew the problem that had probably been giving them grief for years, once I showed them the trick they were queing up to fix them.
The above transistor problem was also found on Hitachi transistors as well as Sony ones, the fault was also present on the semi round type transistor encapsulations as well as the that had rectangular encapsulations, that led me to believe that the conductive deposit some how appeared from something to do with the PC board proccess or it was coming from within the transistor itself or some kind of coating on its leads, it was always on the center lead and radiating outwards, it was dry, scraping the base round the center lead would also cure it if desperate but transistor replacement was the only sure fire cure, but at least I had found a quick way to diagnose the problem...wiggle or stroke...
All that was back in the 70's.
Lawrence.
The subject of transistor problems has taken me back to my days with Sony in Canada.
Back in the seventies at Sony we were starting to get stuff in with various faults but a lot of them seemed to have a familiar "ring" to them, most commonly intermittant problems (the worst) across all types eg: amps, tape decks, tv's etc, some of these were real nasties ie: iintermittant only once in the w/shop...send back out...bounced a few weeks later.
Typically (but not always) the symptoms would be intermittant crackling or noise (like resistor noise) in audio products or intermittant video/IF/chroma problems (colour tv's) it was giving us a real headache.
First approach was the normal one, intermittant = dry joints, out come the blunt end of screwdriver and a knitting needle, bang bang tap tap till your in the area, inevitablely it was the print side of a transistor connection, got to be a dry joint then, out comes the bench magnifier...looks ok but I will resolder the three leads anyway...stick on soak (sometimes for a fortnight) it's fine, send back, next week it bounces...sod it, same proceedure again only find it on a different transistor, same fix, same soak same bounce.
Ok time to nail this little b*****d had a real good luck and a re think as we were now getting a lot of stuff coming in with weired faults and the boss is getting concerned about the back log, normally I'm on the fault within half an hour at most, this was getting to me, anyway as said had a re think, maybe the transistors are responding to taping due to a problem with the transistors internall connections, takes transistor out and checks it, all ok. Eventually a tape deck came in that was intermittant noisy on audio and the intermittant problem stayed long enough for me to find what was causing this problem with the transistors used in most of the Sony products, it responded to the usual taping etc, again narrowed it down to the area of a transistor, wiggles the top of the transistor and the fault aggrevates, must be a dry joint or an internal failure, it was neither of those things although the transistor was to blame, I removed it and had a real close look under the bench magnifier at the base of the transistor (the underside) and there radiating out and under a certain light was flourescence looking deposit (looked like what petrol on water would look like) it radiated out from the center lead (I think that was the collector) and had spread to the other leads and it was conductive, so taping the PC board was enough to cause this conductive connection to become none conductive due to the vibration caused by tapping or wiggling the top of the transistor, the act of removing the suspect with a soldering iron also broke that conductive link but given time, usually a couple of weeks, it would be back to its old tricks again. From that day on finding these nasty intermittant faults caused by the above became a breeze, just slighty stroke or wiggle the top of the transistors and it soon became clear which one was at fault.
When I eventually returned to the UK I needed work so I got a job as a bench tech with a local Radio & TV firm, most of the techs were only used to the usual Thorn, Phillips,ITT stuff, they asked what my favourite stuff was and I told them Sony or other Jap stuff..."Right then you can repair the bl***y lot" which was fine by me as I knew the problem that had probably been giving them grief for years, once I showed them the trick they were queing up to fix them.
The above transistor problem was also found on Hitachi transistors as well as Sony ones, the fault was also present on the semi round type transistor encapsulations as well as the that had rectangular encapsulations, that led me to believe that the conductive deposit some how appeared from something to do with the PC board proccess or it was coming from within the transistor itself or some kind of coating on its leads, it was always on the center lead and radiating outwards, it was dry, scraping the base round the center lead would also cure it if desperate but transistor replacement was the only sure fire cure, but at least I had found a quick way to diagnose the problem...wiggle or stroke...
All that was back in the 70's.
Lawrence.
