I will connect the oscilloscope.

Here's what someone did with Q651-Q654
This heatsink still got 62°C

 

hm, how would it look like if they were oscillating?

Connected to all resistors one at the time, similar on all.
Probe was at X10, see pics

 

I just tried to adjust again....manual says to adjust to 25mV

But as stated earlier, i can't even get that on LEFT side, on this picture VR401 is at "full throttle"
RIGHT reaches 25mV almost at half turn at VR402, i guess that seems more correct.
I tried to switch DMM's just to be sure, showed same.

 

What voltage did you achieve on LEFT channel? If it is 23.6mV then that is good enough.
Did you go ahead and balance VR403 and VR404?

 

What voltage did you achieve on LEFT channel? If it is 23.6mV then that is good enough.
Did you go ahead and balance VR403 and VR404?

Yes that was max at LEFT, VR401 turned fully over.
Did not go further because of the low voltage.

But, if that is good enough, i might set RIGHT channel at the same voltage? And then carry on with next adjustment...

 

I think you’re splitting hairs here.
I would not be too concerned with getting it exact to recommended setting. Any setting between 20mV and 30mV will be fine.
The two channels do not have to match perfectly.

 

Okey, i don't know such things you know

I will try now, but looking at adjustments.. number 3, those adjusters at the volume control PCB board.. i haven't touched them, do i still need to adjust ?

 

Sooo.... i made the adjustment number 1, waited 15 minutes and it turned out fine, with LEFT on max it settled at 25.3 mV... which is good.... i set the RIGHT one at 25.5 mV.
So, i was pleased with that.

Went on to adjustment number 2.
Went fine to turn them both to 3 mV, then i waited to see what they will get to....... doing it by the book.

But after about three minutes Q515 popped !
Came just a little smoke from it, i did not see any other component smoking before i dragged out the plug in a hurry....
I couldn't feel it was hot either... but it is connected to that big heat sink...

What do we do now? oh noo

 

Q515 is in the LEFT Channel power output.

You were having problems setting the current drive on the left channel.

1) Remove Q515.
2) Turn VR401 back to minimum.
3) Reinstall lamp on mains supply.
4) POWER ON
5) measure voltages at:

TP501 +
TP501 -
TP502 +
TP502 -

R459
R461

 

I was about to test now, but nothing happened with power on.

Both 2A fuses at the power switch has blown.
These have survived all testing earlier.
Need to get new ones before testing

 

I suspect there is something flaky with LEFT channel drive circuit.
Leaving VR401 at the max setting meant that at some point the drive is too high and it blows the output stage (and the fuses).

Check VR401 and the resistors around Q417 circuit.

We know from your post #674 the two channels do not match.

 

So i put in new fuses, and i'm using the 100W light bulb.

It now shines pretty strong, indicating a draw....

Voltage seems to increase the longer it is on... i have only let it be on for about two seconds between each measurement.

Measured to GND

TP501- : -25 Volt and rising
TP501+ : -25 Volt and rising

TP502-: 0 Volt
TP502+: 0 Volt

R461: -23 Volt and rising / -8.5 Volt and rising
R459: -6.7 Volt and rising / +2.3 Volt and rising

 

Please remove Q503 and Q505. Test them out-of-circuit but don't put them back yet.

Measure voltages at:
R427
R429
R459
R461

 

So i removed Q503 and Q505, tested out of circuit, both were ok.

Then measured voltage, same as earlier, voltage increases, at R429 one side of the resistors starts to rise to +3 then it turns to -3 in about two seconds.
The voltage does not stabilize.
Still got power draw indicated by 100W lamp

R427: -25 V rising / -3.5 rising
R429: -25 V rising / - 25 V rising
R459: +3 V to -3 volt and rising
R461: -2 volt rising / -25V rising

 

Earlier, before Q515 blowed when i was just comparing channels,
I noticed at IC402 (RIGHT) channel had +1 Volt at Pin1.
At IC401 (LEFT) voltage was +0.1 Volt at Pin1.
-could that have something do to with the low mV at adjusting?

I don't know if this gives you any info at all, but it was just a difference from LEFT to RIGHT side i could find...

I don't seem to find Pin1 at these IC's in the schematic, but now voltage at IC401 Pin1 is -7 V and rising like on all other places.

 

You cannot compare IC401 and IC402 pin for pin. They are not wired the same.
In any case pins 1 and 7 should be just over +1V.

IC401 1st stage amp
1 = OUT +1.3V
2 = -IN 0V
3 = +IN 0V

2nd stage amp
7 = OUT +1.1V
6 = -IN 0V
5 = +IN 0V

IC402 1st stage amp
7 = OUT +1.1V
6 = -IN 0V
5 = +IN 0V

2nd stage amp
1 = OUT +1.3V
2 = -IN 0V
3 = +IN 0V

Something is upsetting the voltages on the LEFT channel 4xx section.
Check the voltages at the transistors and compare with the schematic:

Q411 C= -8.5V B= -58.7V E= -59.4V
Q413 C= +60V B= +8.4V E= +7.8V
Q415 E= -7.9V B= -8.5V C= -60V (PNP)
Q425 E= -0.6V B= -1.3V C= -60V (PNP)
Q429 E= 0V B= -0.6V C= -60V (PNP)

 

Okey i understand, cannot compare

Measured about 2 seconds with power on. Voltage does not stabilize on any measurement. just rise
Q411:
C: -25 Volt
B: -18 Volt
E: - 25 Volt

Q413
C: -3.5 Volt
B: -3.5 Volt
E: -4 Volt
Voltage at these pins are at first +2V, then it turns into minus

Q415
E: -25 Volt
B: -15 Volt
C: -25 Volt

Q425
E: -25 Volt
B: -25 Volt
C: -25 Volt

Q429
E: -25 Volt
B: -25 Volt
C: -25 Volt


After all this power on/off i felt the little black heatsink with Q429 on get a little hot.
SO, i removed Q417, Q427 and Q429, tested them out of circuit, all these measured OK!

 

Something has gone wrong with R505 and R506.
Take those out and check. Replace with the small bulbs again.

Did you turn VR401 and VR402 down to minimum?

Compare voltages between LEFT and RIGHT channels

LEFT RIGHT
Q409 Q410
Q411 Q412
Q413 Q414
Q415 Q416

If it is difficult to get at the legs of the transistors, follow the circuit diagram, getting to a resistor might be easier.

 

Yes i turned down VR401,402,403,404
But before testing voltages, should i install Q417,Q427 and Q429 again?
They are out at the moment..

 

Leave them out for now.

Something is draining the +60V and -60V supply rails being fed by R505 and R506.
Both LEFT and RIGHT channels would be affected. It is a surprise that R505 and R506 did not go up in smoke.
R506 would be passing 5A and would have blown by now.

Basically one of the components (most likely one of the transistors) in the 4xx section is drawing too much current