[time-nuts] Dead 5065A - Some comments - Some questions...

[Ulf Kylenfall]

..Continued.
Having discovered that the A3 multiplier went bad the firsttime after a few hours of service, I checked the A3 unitfrom a scrapped 5065 on my bench. It was neverinserted in the once working unit : DOA....

The problem with some of the plastic packaged FETs wasthe same. Also that output transistor was bad. That 5065
was salvaged from a shed somewhere. Previous ownertook out the 5MHz XO and I remember that there had beensome unsuccessful attempts by previous owner to openthat A3. (I take it that he eventually gave up, took out the5MHz XO and discarded the rest.)

I am therefore of the opinion that either there is a reliabilityproblem with these transistors due to microcracks in the plasticpackages allowing for moisture to reach the silicone waferor long term silicone deterioration that gets accelleratedby applying supply voltage to them again after 30 yearsor so. I have experienced similar problems with other oldinstruments that is powered on for the first time in 20-30years. And I do not mean the RIFA power line capacitors that more or less always let out their smoke...
+20V is rock stable. I will of course check if there are anyunstabilities once all modules are back in place.

The 2N4416 that was previously used as a replacementin my unit did work OK. The output transistor as well. 
And - also the 3N128 - That one is TO-18 hermetic...

About A1: it seems that SN74176 (or possibly 74196)is a replacement for the 1820-0322 - Signetics N8280N. It can not be so difficult to find a modern replacement/modification for the 1820-0315 one-shot should it be necessary to build a completereplica of the synthesizer.


Cheers.

Ulf Kylenfall