Fosgate 600 4 channel

Screenshot attached of negative supply at one of the opamps measured directly from pin4. Probe, ground, nothing moved or changed between the two other then getting u4 hotter

Probe ground at speaker terminal.
 

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99% sure. There’s nothing between the regulators and the torrid or maybe 1cm from its base. The cardboard extends from the pcb to 3” above the regulator and opens towards the torrid, hugging the stamped heatsink.

I’ll keep playing with it though.
 
Ok… so using just a dmm the negative rail starts at -11.2v cold then warms up to -12.4. The positive rail stays at 13.6-7 warm or cold.

Using the 1.25*(1+R2/R1) rule for the regulators I get a calculated output voltage of 13.75. Negative rail is way off - in practice it may not matter but the noise combined with the hunting voltage seems to point to an issue here.

I was careful not to heat the resistors but it’s possible the board is just conducting heat.

R33 is at about 3% but r34 is close to 8% out, cold. I’m going to start by replacing r34 then maybe the regulator
 
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