Does anyone happen to have a picture of the four SMT components near the speaker terminal and mounting hole? They are missing from my board and the component numbers were cleaned off.
I am guessing one of them to be C417.
Your picture helps with two more designations. The missing one is closest to the mounting hole. I'm guessing it could be C416 or C418, so I'll look around the board to see if either of those two are used elsewhere.
Two definitely are connected between the positive speaker terminal and ground.
The pads are gone from where the other two connect together, but they likely connected to ground also.
Here is a picture of what I have.
I have this amp some what working now but it has a couple of issues.
There was some physical damage done to the input caps and little transformer. I replaced the caps and transplanted a round transformer in from another amp. I marked the orientation of the transformer before removing it from the other amp denoting which side went to the drivers and which went to the PS FETs.
With the amp powered up, I get the measurements shown below (5V/div & 5uS). First one is taken at the base of an A56 driver. The second is taken from a transformer leg driving the gate of the PS FET. Seeing half of the amplitude of the drivers at the gates I thought I made a mistake installing the transformer so I rotated it 180 degrees with exactly the same outcome.
I have ~ +/- 14.5V at the op amps and -35.5V & 33.8V (too low?) at the rectifier's and no excessive current draw at idle.
The main problem with the amp is, while it produces clean audio, it clips at ~16VAC (no load) at the speaker terminal instead of an expected ~34.65VAC. I can repeat this consistently by either sending a strong signal in or by increasing the amplifier's gain control. Right now I have the jumpers in place bypassing the preamp board and the little transformer is still installed backward from my original marking.
Is this transformer incompatible or is it defective?
The other problem is the adjustable LED lighting isn't working, which we'll tackle last.
I replaced the two 10 ohm, base to emitter resistors at the drivers.
I replaced the eight 2200uF capacitors due to physical damage.
I replaced the transformer due to physical damage.
I installed the .47uF capacitor across the output terminal.
The previous work I saw was that of the sanded area around the missing surface mount capacitors and there was another sanded area under one of the 2200uF caps.
I see non-original solder around some of the PS FETs, but they all match.