On 12/20/2009 11:24 PM, ivp wrote:
> So the plan is to probably try some instant freeze in places to see if it
> comes back to life and routinely replace all the semis, of which there
> aren't that many, and after 26 years of continuous use it should benefit
> from a good refit, clean and resolder
>    
Having done a fair bit of repair, this sounds somewhat risky to me...

Yes, cleaning, adding a bit of flux, and reheating all/most of the 
joints sounds like a plan (don't forget the flux to help clean up oxides)...

But seriously dismantling a circuit which sounds as seriously put 
together as this sounds like asking for a trace lift or similar, unless 
you are *very* skilled and *very* careful.   Plus, replacing semis 'just 
because' doesn't seem to me to be very useful - who is to say the newer 
ones are any better than the old ones.   Last I checked, semiconductors 
generally do not wear out... unless they are stressed beyond their 
design parameters.

Now replacing any electrolytic caps on the board (and anything else 
which truly will age), that sounds like a plan (and could very well be 
your issue with that old of a unit).

In regards to your mystery part... I did do a bit of searching and 
didn't come up with a helpful cross for that part.  Thought there might 
be an old SGS transistor book in my library, but no luck ...

-forrest
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