Amp not turning on

[sfbadger]

Having a problem with a long-time set-up, there's been no changes to the system.

I get 12V at the power terminal when the car is off, the remote wire gets 0V. So far so good.

When I turn on the radio, I get 10.5V at the remote terminal, but only 4.5V (?) at the power terminal, amp does not come on.

Then I applied external 12V to the power terminal, the amp switched on and played normally. All I had to do was briefly touch the external 12V to the terminal and it would stay on. If I switched off the ignition and turned it back on, the amp didn't turn back on. I did this about a half-dozen times.

The last few times I tried it, the amp would turn on when I applied external power, but wouldn't stay on when removed, the sound would quickly fade out and the amp would turn off. If I maintain external 12V, it works properly.

The protection light was never on at any point. Since power seems to be working as it should, I'm guessing my 20+ year-old amp has given up the ghost, but I thought I'd see if there was something I was missing.

I pulled the amp and checked out the circuit board - nothing obvious

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