Sheesh

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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.

Re: Sheesh
On Saturday, February 27, 2021 at 12:42:20 PM UTC-5, snipped-for-privacy@gmail.com wrot
e:
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 already been gone through but I think I have ALMOST seen it all.  
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ed outputs though I don't know why.  
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 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 ?  
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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.  
Quoted text here. Click to load it
  
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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.  
Quoted text here. Click to load it

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.



Re: Sheesh
On Sat, 27 Feb 2021 12:27:16 -0800 (PST), " snipped-for-privacy@gmail.com"

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It was the 2SC458s.

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



Re: Sheesh
On Sunday, February 28, 2021 at 3:07:06 PM UTC-5, snipped-for-privacy@gmail.com wrote:
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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.
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 the chip.  
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Yep.  I think Chuck one post up identified the number.  


Re: Sheesh

  snipped-for-privacy@gmail.com wrote:  

===============
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** See:

https://www.oneonetwo.com/2013/07/vintage-transistors-2sc458-hitachi.html

That looks  *horribly " familiar....  


....   Phil  


Re: Sheesh
On Sat, 27 Feb 2021 12:27:16 -0800 (PST), " snipped-for-privacy@gmail.com"

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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

Re: Sheesh
On Tuesday, March 2, 2021 at 9:09:12 AM UTC-5, legg wrote:
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rote:  
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has already been gone through but I think I have ALMOST seen it all.  
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eeded outputs though I don't know why.  
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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 ?  
Quoted text here. Click to load it
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.  
Quoted text here. Click to load it
t.  
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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.  
Quoted text here. Click to load it
 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.  
Quoted text here. Click to load it

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.

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