Peavey Backstage - Constant Loud Hum

[PorteX]

Hello,

I tested the voltages using two different millimeters (both of them are form China but I compared them with a better multimeter and the readings was simialr)

R49 and R51 both are 10 Ohm like in the schematics but I can replace them with 10k Ohm to check if there will be any difference.

I have a spare 4558p so I compare them outside the circuit using diod test in the mulimeter ( I saw some vidoes on the youtube) and both of them have the same readings. Despite this I have replaced the 4558p but nothing has changed.

I was thinking about replacing Q10 even though the diode test showed it is OK, but I don't have a similar transistor.

[PorteX]

Hello all,

I have replaced the R49 and R51 with 10k Ohm, after that I had -4V and 1.5V on 4558p, so I have decided to put 1k instead of 10k and there is a progress...
The Constant Loud Hum disappeared and now I can even hear music when I'm connecting my laptop to TAPE/CD jack, but is is working only on a specific volume knob position.
When the correct position is set I have around +19V and -19V on 4558p and no DC on speaker but if I slightly change the position of volume knob the music is gone and the voltage on 4558p is +9V and -18V and I see 6V DC on speaker.

[PorteX]

Hello,

For the tests I have replaced the Volume potentiometer from 50k to 100k (I don't have any 50k) and now the Amp is working.
Now the voltage on the 4558p pin4 and pin8 is around +/- 18.5V with the R51 and R49 1kOhm

Many thanks for your help.

[g1]

Now the voltage on the 4558p pin4 and pin8 is around +/- 18.5V with the R51 and R49 1kOhm

Can you check what is the value of R50 in the amp? Maybe 10 or 100R ? And what voltage on each side of it?
Thanks

[PorteX]

R50 is 1k Ohm, and the voltage is 24,4V on one side and 22.6V on other side.