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SONY TA-5650 DC balance and bias adjustment

S

seventies61

New Member
After installing the new pairs of 2sj18 and 2sk60 in my Sony TA-5650 and with good power voltage adjustment, the confirmation of DC balance voltage "speaker out A right" is 36mv (manual + - 50mv), nice, but the "speaker out A left" is 150mv! How to adjust that?

I have no readings for DC bias adjustment with the manual procedure so adjusting RT 301 and RT 351 for 90mv reading is not possible. How to do that. Thank you for your answers.
 
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You have to get the bias current flowing before you can trust the offset readings. The amp board has four VD-1221 diodes that are nearly always a problem. Replace each VD-1221 diode with a pair of serised 1N4148 diodes. Bias should come back, unless there's some other major problem.
 
Done. The four VD-1221 diodes have been changed with a pair of serised 1N4148 diodes and the bias adjusted to 50mv (service manual asks for 90mv but Sony asks later for 50mv). No change with the DC balance voltage "speaker out A right" is 40mv (manual + - 50mv), nice, but the "speaker out A left" is 155mv.
 
Not on the 5650. No offset adjust.

To get offset down, replace Q302 and Q303 (or the other numbers for the opposite channel) with matched pairs. The best replacement would be a Zetex ZTX795A, but you'll need to have them closely matched for gain, which means buying 15 or 20 of 'em.

If you are in the US, and need help with matching, email me through my profile and I can help.
 
Thank you very much for your great informations and attention. I live in Switzerland, I will try to find the Zetex here.
One more thing: one channel have 1 pair of 2SK60/2SJ18 rank 55 and 1 pair 2SK60/2SJ18 rank 56 (The right channel with good readings). Is this a problem?
 
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