Behringer schematic versus actual board

[AngelB]

I’m a musician who has been out of work due to covid so I’ve been repairing old gear that has been sitting under my work bench. I’m down to the last item, a Behringer K1800FX keyboard amp. I have the schematic, but the board is burnt through. I’d replace it but Behringer is notorious for having shut down their product support a few years ago. That said, I’m finding a lot of parts on the board that disagree with the schematic. I’m also finding silk screened markers on the board that disagree with the schematic. This is going to be interesting. Here is the schematic.

 

[AngelB]

Here is the board.

 

[Harald Kapp]

The schematic shows revision F:

Find the revision of your PCB (it should be somewhere printed or etched onto the PCB). Designs vary between revisions. These can be small changes to fix defects or radically new designs, depending on the reason for the new revision. You'll have to find a schematic for the same revision level as your PCB.

 

[AngelB]

So far I’ve found one resistor and two diodes that aren’t the same on the board as the schematic, though the diodes are the same as the voltage marked on the board. I’m amazed it worked for as long as it did. They installed 15V 1W Zener diodes where the schematic calls for a 1N4007 1000V 1A rectifier diode.

 

[AngelB]

The schematic shows revision F:
View attachment 51598
Find the revision of your PCB (it should be somewhere printed or etched onto the PCB). Designs vary between revisions. These can be small changes to fix defects or radically new designs, depending on the reason for the new revision. You'll have to find a schematic for the same revision level as your PCB.

Looks like the board is revision J. I don’t know if it will be available. I had a heck of a time finding the one schematic for revision F

 

[Harald Kapp]

I had a heck of a time finding the one schematic for revision F

I believe that , but it will be necessary. 4 revisions apart - that could be an entirely different circuit.

 

[AngelB]

Damned if I’m not luckier than I know. Someone posted it on Scribd and I managed to snag a photo of it, just a second ago. I hunted for three weeks just to find revision F. Thanks for the info and advice, Harald. It’s still going to be a complicated project but having the right schematic will help. Now if I could only find a good photo of the board traces. Some of them burnt through and I’ll have to recreate them.

 

[Harald Kapp]

Some of them burnt through and I’ll have to recreate them.

With the schematic at hand you can simply use enameled wire (magnet wire) to make the necessary connections. Fortunately neither circuit nor board look too complex.

 

[AngelB]

Looks like the revision J I found is illegible, but I’ll keep searching. Thanks