onkyo a-8015 integrated amplifier

[adason]

Hi all,

I need your help in getting Onkyo Integra A-8015 up and runnig.
I got this amp chieply because it was dead. I quickly measured output transistors were fine, but there was 19 volts on the output, so the speakers relay was not enagaged due to DC protection.
I got schematics from the net, and measured voltages. Power supply is +/- 42 volt, but preamp section works from +/- 22 volts. One section was down. I replaced zener diod and mosfet and got symetrical voltages. Amp clicked as speakers connected. Great. However, one side still has about 1.5 vol DC on the output. The other is exactly 0 volts. I have been looking at the servo section, but can not figure out which part is responsible for offset.
I need help. I do not want to drive speaker with 1.5 volt DC.
Otherwise amp sounds sweet on headphones.

Thanks,
Ed

ps: I have manual and can email it, I will try post the amp schematics

[adason]

schematics

[sakis]

device that old for sure has leacky electrolytics...... you need to make sure that all are working fine
also replacing them is a good start

an easy way to find out were the fault is is to use a multimeter but in an alternative way

means you dont check voltage point to ground but actually you check one lead to resistor bla in chanel one and then the same resistor bla bla on the faulty chanel ....the measure is between them and not to ground
if the circuit is fine you will get a few millivolts if more there is a problem

check this also you might find it handy

vintage amplifier repair/upgrade manual

[Rafael L]

The problem is in two channels?

[adason]

The problem is in two channels?

no, just one, the other has precisely 0 volts on output

thanks for the link sakis, will have a close look!

ed

[adason]

I have some progress...I traced the problem to somewhere around D501 diode in the base of Q504. It seems when I replace this diode with other, I get different DC offset on the base of Q506 which than reflect is different Q506 collector voltage. This voltage is important to be close to 0.1 volt. I have swapped D501 diode with some and found one which gives only 0.1 volt on the output. Now that is much better than previous 1.5 volts. Amp has been playing beautifully in the livingroom last few days without problem. It replaced old Tandberg receiver, which is due for good cleaning.
ed