JL Audio 500/5 Muting

Well I did get mute worked out.

But now looking at the AB channels one of them has this distortion.

Is this likely a driver card issue?

The signal looks correct coming off the preamp board.
 

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This is the muting circuit. The muting for the 4 channels needs to have negative voltage to drive the jfets off (stop clamping audio to ground).

Initially, there was no negative voltage. Post 17 showed that the 3B transistor was pulling the 1B base up but the collector wasn't being pulled down. That meant that the transistor was open.

When you replaced the transistor, there was some negative voltage but not enough to drive the jfets off. In post 28, there was some negative voltage on the collector of the 1B transistor but the Vbe was too great. That meant that the base junction was damaged.

In post 33, the voltages were right. The Vbe was about 0.6v and the collector was being pulled down to near the emitter voltage.

If the 10k resistor is still in the circuit, you can remove it to see if the 1B collector is still very near its emitter voltage.