ACA failed after a decade Help diagnois

I build my aca's at the first ever amp camp back in 2012. They have served well for over a decade until recently when one of them stoped producing. I checked all the obvious external connections/wires and source and they are all good. I opened it up and that's as far as I've gotten. I don't know what to do next. It is my understanding that is the very first version of the amp. Hoping to repair it so I can pair it back up with the other one and keep on listening.
Thanks for taking interest.
If you have a volt meter handy start with the power supply. Unplug it from the amp and measure it.

If there is voltage - plug it back in and measure it inside at the supply input connector. Then proceed to the power. Switch and measure it on both sides.

Conversely if there is no voltage. Likely the supply decided to take a vacation.
The power supply is rated at 19 volts My volt meter may not be the most accurate but it measures 20.1 at the switch (a lighted switch) and 20.1 where the + - attach to the board. The power supply is hardwired (soldiered) to the switch and board so I can not test it separately without braking the soldier joint.
Are your heatsinks warm?

It doesn’t take much current to light the LED.

But is possible that your switch, or power supply connector can no longer sink the current required to turn on and run the amplifier. Kind of like a car with a loose battery cable. The overhead light comes on when you open the door but the current of the starter is too much for the loose connector.

If the heat sinks are cold. Take an alligator clip, or screwdriver and go across the switch and see if the amp will start.
Joined 2012
Paid Member
It is time to measure some Voltages. Measure the Voltage across R9 and R15.

Measure the Voltage at the drain of Q1 relative to ground.

If you adjust the trimmer pot, does the Voltage at the drain of Q1 change?

If you adjust the trimmer pot, does the Voltage across R9 change?

Is the LED on?

Post some well lit and focused pictures of the amplifier showing all wiring and connections and pictures of the board.
My board does not have an R 15
I'm not sure which is the drain at Q1
On my working amp at Q1 I get 0 volts (left), 10.5 volt (middle) 4.4 volts (right)
On the non working amp I get 0 volts left 7.6 volts (middle) 7.2 volts right.
One thing to note. the voltage at the middle connection on the non working amp starts around 12 volts and slowly drops to 7.6 volts
Here are pics of the two boards.


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Joined 2021
Paid Member
The wire is not broken. If I set the multi meter at 2000k it reads around 275. This amp was working for the past 10 years and just stopped. It is built into a cabinet that does not move. So it should be safe from physical damage. I think something must have burned out.
You can't measure the resistance of R10 when measuring across the resistor while it's in the circuit.