Vintage Synth Repair

On Saturday 03 May 2008 13:54, scott frye wrote:
> In my 25+ years on working in engineering and test I've seen VERY VERY few
> op amps ever go bad. Caps crap out far more and power resistors and 3
> terminal regulators

Well,  I've been a tech for around 40 years,  and I have.  Lots of 1458 and 
4558 op amps go bad,  typically with the output sitting at the negative 
supply rail.

Caps,  yeah,  sometimes,  but I think that the whole recapping things is 
getting way out of hand.

Power resistors?  Sometimes,  but not that often.

3-terminal regulators?  Only if you abuse them,  or in poor designs.  Last 
time I managed to kill a couple of 7805s was way back in 1975 or so,  when I 
didn't really understand the requirements and didn't have enough heatsinking 
on them,  and continuous thermal cycling (taking it into shutdown and keeping 
on going there) will kill 'em sooner or later,  but since then _very_ few of 
them.

Easy test for op-amp fuinctinality:  Short the inputs.  Usually there's enough 
resistance in line with either or both of them that they won't see a problem 
in the driving circuitry,  and the pins are usually also right next to each 
other so the smallest handy screwdriver is workable if you have good lighting 
and a steady hand.  The output should go to halfway between the rails.  If it 
sits on one rail or the other it's bad.

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
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