Much of the time, when parts in a circuit that is correctly designed and built burn up, the failure is in some other part. In this case it appears that the problems are in one of two channels in a stereo amplifier.
So prior to burning up more parts, please show us the circuit schematic and a description of which parts are burning up, so that the trouble can be traced. AND learn how to correctly use your meter. I saw a terrible accident that happened when an unknowing person used a meter with the leads in the current connection and put them across a 460 volt 50 amp circuit. Not only did it destroy the meter, it also burned the probes out of his hands. The person did survive, the meter was nailed up on the wall as a reminder to check the connections first.

 

The schematic is on page 35 about the middle. It is a direct coupled circuit with the problem being anywhere from the front end on. In my day, I would pull each transistor and check in a transistor tester.

 

I removed R505 and R506, and put it the 21W bulbs again, they are not glowing when power on, and the power draw is almost none now after replacing the resistors with the bulbs.

Tested R505 and R506, both measured 6.3 ohm.. so they are not blown... but not correct either.

I did check all X4 transistors on LEFT channel earlier !! what could have killed one of them now again....
In all this testing i just noticed Q413 gets HOT !!

Measurement:

Q409:
E: +38 V
C: -11.5 V
B +38 V

Q410:
E: +38 V
C: +8.3 V
B: +38 V

Q411
E: -38 V
C: -27 V
B: -38 V

Q412:
E: -38 V
C: -8.3 V
B: -38 V

Q413:
E- 12V
C: +38 V
B: -11.8 V

Q414:
E: -7.6 V
C: +39 V
B: +8.3 V

Q415:
E: -38 V
C: -38 V
B: -27 V

Q416:
E: +7.6 V
C: -39 V
B: -8.3 V

 

Measure the voltage at the 21W lamps, voltage in, voltage out, both lamps.

Measure voltages at:
R401
R402
Q403
Q404
Q407
Q408

 

Lamp at R505: +38 V / +38 V
Lamp at R506: -38 V / -38 V

R401: -15 V / 0 V
R402: 0 V / 0 V

Q403:
E: -38 V
C: -15 V
B: -38 V

Q404:
E: -38 V
C: -0.8 V
B: -38 V

Q407:
E: -18 V
C: -38 V
B: -15 V

Q408:
E: -0.1 V
C: -38 V
B: -0.8 V

 

From post #692 onwards, is the 100W light bulb glowing?

 

From post #692 onwards, is the 100W light bulb glowing?

About the bulb glowing, i don't really know what to expect.. i guess it will always glow slightly when the amp is on, because of the loss in the transformers, and also.. Q651-Q654 dissipation... ?
But earlier when it was "completed" the bulb was glowing very little.

After the incident with Q515, it was glowing much more!
But after replacing R505 and R506 glowing almost fell back to how it was earlier when it was complete.

See video how it is now.

 

We are seeing 38V on what is supposed to be 60V.
I am going to assume that the 100W bulb is dropping the voltage. That should be ok for now while we are testing.

There is an imbalance in the 4xx section from Q401 onwards. We have to remedy that first before moving on.
Something is pulling the mid-point lines (that ought to be around 0V) down to -38V. I will look at your measurements more closely.

 

Yes i believe the voltage drop is because of the bulb.

As i mentioned above, Q413 get’s hot and i believe it will smoke if i leaved the power on.

 

I am aware that Q413 is getting hot, but it might not be the problem, only the symptom.
When you take voltage readings, compare them with those written on the schematic.

R401 should have 0V not -15V.
Hence we have to find what could be supplying -15V.
Try removing IC401 and check the voltage at R401 again.

 

Okey..

I removed IC401 , Power on, R515 smoked.

R515 (2.2ohm) is now open circuit.

-15 Voltage at R401 is now gone. measures 0 Volt at both sides.

 

Remove Q507 and Q509.
Insert a new IC401

 

Remove Q507 and Q509.
Insert a new IC401

okey. Then power on?

 

Yes. Power ON and measure some voltages (anywhere and compare with circuit diagram):

Q413
Q415

Q414
Q416

 

I removed power transistors at LEFT channel and tested out of circuit, both Q507 and Q509 is shot, so i removed Q517 too, it was also shot.

Installed new IC401

Now the 100W light bulb indicates less draw, and the 60V has increased from 38 V to 46 V...

Now it looks better... and Q413 doesn't get hot...
But where should we go from here..

Q413:
E: +7 V
C: +46 V
B: +7.6 V

Q414
E: +7.6 V
C: +46 V
B: +8.3 V

Q415
E: -7 V
C: -46 V
B: -7.8 V

Q416
E: -7.6 V
C: -46 V
B: -8.3 V

 

That looks promising.
Put back the transistors removed. Leave out Q515 and Q517 for now (or leave them in if they are already in place).

(btw, a thermal imaging camera comes in handy for identifying hot spots. Not suggesting that you get one as they are very expensive. However if you have access to one they can be very helpful.)

 

I actually have access to an mobile phone with a thermal camera, it doesn't have the best resolution but it might work...

I have now installed all transistors in LEFT channel again, also replaced R515 with a new resistor.

I do not have any of the power transistors in at LEFT channel now. you want me to install Q509 and Q507 ?


Power on, the 100W bulb is barely glowing.

Thought i was going to try the thermal cam now just to check if something stands out..

 

Yes. Install Q507 and Q509.
Measure some voltages.

 

Ok, i will install Q509 and Q507 and check som voltages at the same points as earlier..

After idling about 5 minutes..
Can't see anything special... it's like it was earlier.
C425 get's a little more hot then C426, but it's so low temperature i guess it doesn't mean anything.

 

Installed Q507 and Q509
What is out of the circuit still is Q515 and Q517.. i wil need supplies for these.. i've placed an order.

Power on.

100W bulb indicates low draw, and the voltage goes up.

I just checked the transistors as earlier:
Any other place i should check voltages?

Q413:
E: +7 V
C: +47.5 V
B: +7.6 V

Q414:
E: +7.6
C: +47.1 V
B: +8.3 V

Q415:
E: -7.1 V
C: -47.5 V
B: -7.7 V

Q416:
E: -7.6 V
C: -47.5 V
B: -8.3 V