I tried to pull CR130 off, in case one of the diodes is damaged, but no change.
Then I checked (rapidly I admit) all resistor values: they're within tolerances, and with very symmetrical values. For some, I must pull out the ICs since their presence alters the measured value. I will do in the weekend with more calm and patience.
All the small power resistors appear to be carbon film rather than carbon composition. It seems quite reasonable to me since the p.c.b. is a latest version: in fact it carries the S/N 670-2323-08 with the "08" applied with a sticker.
In the meanwhile, I checked carefully the resistors in the input source follower. I found R133, a very little composition resistor, marked 16 ohm 5% (brown-blue-black-gold).
On the schematic is marked as selected (selected and added if necessary). The measured value is 20.3 ohm.
It's clearly out of tolerance, but I'm not sure it affects the signal.
Or maybe yes: I think it affects the polarization of the Q150A fet.
What do you think?
Should I replace it with a modern metal film resistor or must I necessarily use a carbon comp. one?
Max
