I tried all the amps, the caps and the 4558D, nothing gets hot, not even warm. Can I somehow check if the power supply is working properly?

There are three wires coming from the power supply (1xblack, 2xyellow). From black to yellow I have 11.9V and 12.4V. From yellow to yellow I have around 24V. After the rectifier bridge I have 31V.

Those voltages should correct (I assume the yellow to black and yellow to yellow measurements are VAC and the post rectifier are DC volts).

Double check that the filter caps are the correct direction. The one to positive rail and common should measure 16.5 volts between positive of bridge and black of transformer and (-) mark on cap should be connected to black of transformer.

The second cap should have (-) lug of cap connected to (-) of bridge and other side of cap connected to black of transformer.

 

I tried all the amps, the caps and the 4558D, nothing gets hot, not even warm. Can I somehow check if the power supply is working properly?

There are three wires coming from the power supply (1xblack, 2xyellow). From black to yellow I have 11.9V and 12.4V. From yellow to yellow I have around 24V. After the rectifier bridge I have 31V.

Double check those voltages. To me, 11.9 and 12.4 seems like a bit too much difference for this type of supply.

 

Double check those voltages. To me, 11.9 and 12.4 seems like a bit too much difference for this type of supply.

You are right, one diode might be bad in the bridge.

 

Those voltages should correct (I assume the yellow to black and yellow to yellow measurements are VAC and the post rectifier are DC volts).

Double check that the filter caps are the correct direction. The one to positive rail and common should measure 16.5 volts between positive of bridge and black of transformer and (-) mark on cap should be connected to black of transformer.

The second cap should have (-) lug of cap connected to (-) of bridge and other side of cap connected to black of transformer.

Yes, voltages are VAC before the rectifier and DC after the rectifier. The caps seem to be in the correct direction and I get -14.7VDC between GND (the black from tarnsform) and the negative rail (after rectifier). For the GND and postive (after rectifier) I get 16.9VDC.

Double check those voltages. To me, 11.9 and 12.4 seems like a bit too much difference for this type of supply.

I have measured again and it's actually 11.9VAC and 12.1VAC with load and 12VAC and 12.2VAC without load.

You are right, one diode might be bad in the bridge.

I don't think the diodes effect this voltages, as they are before the rectifier bridge.


It seems I can't find the problem, so I'm thinking about building a new 2.1 amplifier circuit with the TDA2030/UTC2030s I can salvage from this circuit. Something like this, just with bridged amplifiers for the subwoofer.

 

Try replacing all four rectifier diodes.

 

Ok, I'll try. Just one question. The diodes in the current circuit are 1N5401 (3A/100V). I have just 1N4001 (1A/50V) here which have to small current rating, as the transformer has 2.6A output. So I have to buy some.
Unfortunately my local electronic shop doesn't have the 1N5401, but they have 1N5822(3A/40V). Is 40V sufficient and I can use them instead?

Thanks

 

Give it a shot (1N5822) and see what happens.

 

Changed the diodes and it's still humming

 

Yes, voltages are VAC before the rectifier and DC after the rectifier. The caps seem to be in the correct direction and I get -14.7VDC between GND (the black from tarnsform) and the negative rail (after rectifier). For the GND and postive (after rectifier) I get 16.9VDC.

Something is loading down the power supply. What's strange is that you said nothing is hot. Or maybe the transformer got partially shorted which is not very common. Hmm..

Are you sure the new diodes are in correctly?
Also, try isolating the power supply from the amplifier IC's. It might be easiest to cut traces and repair them rather than removing all of the IC's.

EDIT: I looked back and see the DC voltages have the same unbalance as before the new diodes.

 

It's time to find someone with a scope.