brainbanger
Member
Hi guys,
just a short intro: I am from Berlin, Germany and in my mid-50s. The latter might be the reason why I started digging into vintage audio receivers and it developed into being my main hobby now. I started with a SX-535 and found this forum with tons of hints and tips and was able to fix the unit. I am very pleased with its sound but nevertheless went on with a SX-790, which now is the reason for posting here for the first time. Enough said, what's my problem?
I managed to find and fix a number of dead joints, a shorted Q20 (did replace Q25 and Q19 as well), a dead STK-0050 and one of its .22 ohm resistors, cleaned and deoxited the unit, cross-checked the important DC readings and - the thing died 10 minutes w/o being challenged (IPod via AUX on low volume). :scratch2:
After re-checking everything and reading all relevant posts here I ordered a new pair of Darlingtons (the just implanted ones are dead) and transistors Q11 -Q16 (just in case). Everything else showed no abnormal readings or shortages (incl. diodes, various resistors, etc.). Just finished the soldering job and the unit works ok - BUT: the DC readings make me crazy! Where there should be around 39 volts, I have +47.3 an -47.3! Pin 38 measures 12.5 Volts?!? So what is going on here?
Note: It is a Euro version with 240VAC. Everything else looks good to me, DC from the transformer reads around 40 Volts and nothing overheats.
Can someone please guide or advise me what to do? I am meanwhile used to soldering and metering, SX-780 SM and scheme are with me.
Many thanks in advance,
Andreas
just a short intro: I am from Berlin, Germany and in my mid-50s. The latter might be the reason why I started digging into vintage audio receivers and it developed into being my main hobby now. I started with a SX-535 and found this forum with tons of hints and tips and was able to fix the unit. I am very pleased with its sound but nevertheless went on with a SX-790, which now is the reason for posting here for the first time. Enough said, what's my problem?
I managed to find and fix a number of dead joints, a shorted Q20 (did replace Q25 and Q19 as well), a dead STK-0050 and one of its .22 ohm resistors, cleaned and deoxited the unit, cross-checked the important DC readings and - the thing died 10 minutes w/o being challenged (IPod via AUX on low volume). :scratch2:
After re-checking everything and reading all relevant posts here I ordered a new pair of Darlingtons (the just implanted ones are dead) and transistors Q11 -Q16 (just in case). Everything else showed no abnormal readings or shortages (incl. diodes, various resistors, etc.). Just finished the soldering job and the unit works ok - BUT: the DC readings make me crazy! Where there should be around 39 volts, I have +47.3 an -47.3! Pin 38 measures 12.5 Volts?!? So what is going on here?
Note: It is a Euro version with 240VAC. Everything else looks good to me, DC from the transformer reads around 40 Volts and nothing overheats.
Can someone please guide or advise me what to do? I am meanwhile used to soldering and metering, SX-780 SM and scheme are with me.
Many thanks in advance,
Andreas