Well, it seems strange to me that there's 0V everywhere. Should I try connecting it without the bulb?
Maybe some other measurements to find out what's going on?

 

Well, it seems strange to me that there's 0V everywhere. Should I try connecting it without the bulb?
Maybe some other measurements to find out what's going on?

No. Keep the bulb.
When you apply power and turn on the power switch, does anything turn on on the front panel?
Does the bulb glow dimly?

I need to look at what boards need to be connected.

 

when the front panel is connected this is what it looks like

https://drive.google.com/file/d/1SpKV9GUxxPr4zTeVgBztVsOVnF9YVrmk/view?usp=drivesdk

 

Go back and measure the B, C, E voltages at Q557, Q559, Q558, Q560.

 

the measurements are crazy, the value changes every time.

https://drive.google.com/file/d/182pb7014l1gQQ3khtMUrbNryxhzoTSkq/view?usp=drivesdk

 

Where are you connecting the BLACK lead of the DMM?

 

is connected to the amplifier housing

 

Try this for supply GND.

 

the motherboard was screwed to the case, in this exact place, during the last measurement

 

What happens when you plug the power cord directly into a power outlet (and not into the lamp box)?

 

I just did it, nothing is burning, the voltage is jumping just like in yesterday's video

 

I just did it, nothing is burning, the voltage is jumping just like in yesterday's video

Something has changed from your previous measurements. Either your test meter is not working properly (check it against a known battery) or something in the power supply of the amplifier has changed.

1) Check your DMM on AC voltage on the house AC power.
2) Check the DMM on DC voltage on a battery.

3) Check AC voltage at the secondary winding of the transformer (or at J22).
4) Check DC voltage at the output of the bridge rectifier (or at C609 and C610).

 

1) Check your DMM on AC voltage on the house AC power : measurement OK

2) Check the DMM on DC voltage on a battery : measurement OK

3) Check AC voltage at the secondary winding of the transformer (or at J22) :

J22 : 1-2 = 43v
3-4 = 43v

4) Check DC voltage at the output of the bridge rectifier (or at C609 and C610) : measurements in the photos if I understood correctly what you mean


measurements with a light bulb

 

Ok. Your DMM is good.
The raw DC voltage at the PSU is good.

Now we need to trace to the amplifier and find out why V+ at Q557 and Q558 collectors and V- at Q559 and Q560 collectors are not steady.

This is a direct connection from the PSU to the power amp.

We must be missing something very simple.

 

I'll also add that when I first connected the amplifier to a light bulb, the Q557 transistor and the area around the rectifier bridge got hot. This hasn't happened since. Nothing on the motherboard heats up during my last measurements. Perhaps something got damaged then...

 

V+ from the PSU connects directly from C609 to the collectors of Q557 and Q558 (via jumpers).
V- connects from C610 to collectors of Q559 and Q560 (via jumpers).
With the power removed, check for continuity. Maybe the tracks or jumpers are burnt out.

 

If I marked everything correctly, the continuity measurement is OK

rectifier bridge + -> C609 -> C: Q557,Q558 -> OK
rectifier bridge - -> C610 -> C: Q559,Q560 -> OK


DC current measurements seem strange, should the polarity be reversed?

 

If I marked everything correctly, the continuity measurement is OK

rectifier bridge + -> C609 -> C: Q557,Q558 -> OK
rectifier bridge - -> C610 -> C: Q559,Q560 -> OK

DC current measurements seem strange, should the polarity be reversed?

The important point is that the voltages are stable.
Now, go back and make the measurements at Q557-Q560, B C E
If the voltages are stable, do the same at Q501-Q504.

 

Now, go back and make the measurements at Q557-Q560, B C E

Measurement to the bridge rectifier or ground?

If to ground, neither measurement is stable; it looks the same as last time.