Sound Technology 1710A

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My Sound Technology 1710A Audio Measurement System unit has developed a vacillating distortion which apparently is in the master oscillator.
The unit specification for generator output THD is below 0.04% … very clean. Just recently it has jumper up to around 0.15%.
Has anyone seen this problem ??
This unit uses a notable number of 2605 op amp ICs which appear to be super 741s in a TO-22 8 pin can with the can coming to pin 8 for grounding purposes. Any information on this unique IC would be appreciated.

Thank you.
 
I own a 1700B, which should be quite similar.

I have had a number of problems along the years, here they are in as much as I can recall them:
-Faulty 723 in the supply section; unrelated to your problem
-Bad contacts in the connectors, the flying leads going to TP's on the boards; possible culprit
-Faulty optocoupler; idem
-Noisy and out of tolerance carb comp resistor; idem
 
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