Sheesh

Lately I work on audio and have long thought that I get the shit that has a lready been gone through but I think I have ALMOST seen it all.

This amp in a receiver, not the greatest but is vintage, whatever it needed outputs though I don't know why.

So it is offset bigtime. The problem ? A 27K going to the emitters of the d iff pair. So with that replaced it centers the voltage and all it supposeed ly well but it has distortion. Wracked my brain or a bit and I decided to go inoto detail mode. What do I find ?

An 2.2K ohm resistor where an 18 ohm belongs. What's more it looked like it had never been changed or if so it was a very long time ago because the co nnections had the same dust on them as the rest of it.

Shit like this is not normal, and I am dealing with more and more of it.

Then there is this quad unit, outputs good but it had more bad transistors than you could sweep off the floor. get the amp fixed and a channel is cutt ing out. Bad connection ? Nope, a transistor. Got that fixed and now off to another board that is no doubt full of bad transistors.

Life is trip, think of the destination.

Reply to
jurb6006
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On Saturday, February 27, 2021 at 12:42:20 PM UTC-5, snipped-for-privacy@gmail.com wrot e:

already been gone through but I think I have ALMOST seen it all.

ed outputs though I don't know why.

diff pair. So with that replaced it centers the voltage and all it suppose edly well but it has distortion. Wracked my brain or a bit and I decided to go inoto detail mode. What do I find ?

it had never been changed or if so it was a very long time ago because the connections had the same dust on them as the rest of it.

s than you could sweep off the floor. get the amp fixed and a channel is cu tting out. Bad connection ? Nope, a transistor. Got that fixed and now off to another board that is no doubt full of bad transistors.

The only time I really remember transistors being a red flag (other than ea rly Germaniums) were some small Hitachi signal transistors from the 70s-80s - the TO-92 ones with the beveled top. Those things would go leaky or ope n or intermittent (their choice). It got to the point back then that I jus t automatically changed them whenever I saw one in anything I worked on. Pr etty much eliminated any rechecks.

Reply to
ohger1s

It was the 2SC458s.

Reply to
Chuck

snipped-for-privacy@gmail.com wrote: =======================

early Germaniums) were some small Hitachi signal transistors from the 70s-8

0s - the TO-92 ones with the beveled top. Those things would go leaky or op en or intermittent (their choice). It got to the point back then that I jus t automatically changed them whenever I saw one in anything I worked on. ** You talking about the the dreaded " black leg corrosion" problem ? TO92s and the like with silver plated leads.

Silver sulphide would form on the plating, travel into the device and eat the chip.

Always Jap stuff like Marantz.

..... Phil

Reply to
Phil Allison

n early Germaniums) were some small Hitachi signal transistors from the 70s

-80s - the TO-92 ones with the beveled top. Those things would go leaky or open or intermittent (their choice). It got to the point back then that I j ust automatically changed them whenever I saw one in anything I worked on.

the chip.

Yep. I think Chuck one post up identified the number.

Reply to
ohger1s

===============

** See:

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That looks *horribly " familiar....

.... Phil

Reply to
Phil Allison

We had an issue with parts in TO98, which was a common package for early GE plastic signal transistors. 2N339x 2n34xx. These were encapsulated off-shore, possibly even a simple rebrand.

At the time, there was a suspicion that they weren't normal supply chain product, as the bad parts were purchased through brokers.

Although conforming to TO98 outline, they were a filled-epoxy package, vs a molded epoxy. Anything showing up with the filled-epoxy construction was simply dumped at incoming inspection. Rubbish.

RL

Reply to
legg

rote:

has already been gone through but I think I have ALMOST seen it all.

eeded outputs though I don't know why.

the diff pair. So with that replaced it centers the voltage and all it supp oseedly well but it has distortion. Wracked my brain or a bit and I decided to go inoto detail mode. What do I find ?

ke it had never been changed or if so it was a very long time ago because t he connections had the same dust on them as the rest of it.

t.

tors than you could sweep off the floor. get the amp fixed and a channel is cutting out. Bad connection ? Nope, a transistor. Got that fixed and now o ff to another board that is no doubt full of bad transistors.

early Germaniums) were some small Hitachi signal transistors from the 70s-

80s - the TO-92 ones with the beveled top. Those things would go leaky or o pen or intermittent (their choice). It got to the point back then that I ju st automatically changed them whenever I saw one in anything I worked on. P retty much eliminated any rechecks.

We've all seen flat out counterfeits. When I used to repair an amplifier w ith blown outputs, I used to return them along with a copy of my do's and d on'ts - things like checking for wayward strands of speaker wires, looking for speaker wires punctured under carpet strips, not doubling up speakers o n one terminal block, leaving sufficient ventilation on top of the amplifie r, etc. I remember when I had amplifiers coming back with reblown outs, a nd I blamed the customer. Turns out the semis I was buying were counterfei ts, and it wasn't just audio transistors. We ran into this problem with te levision vertical output ICs, power supply ICs, horiz (line) outputs, STK convergence modules, and even Sony jungle ICs.. I remember going through m y parts supply and tossing a good portion of them out and making sure to bu y from only reputable suppliers or directly from the OEM.

Reply to
ohger1s

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