Mackie 808M

[clintronics]

I have an 808M that seems stuck in mute mode.

Can anyone explain how this mute circuit is supposed to function.

thx

[Jazz P Bass]

Is the circuit muted or is the amplifier in protect mode?

[clintronics]

Muted

[Brian Swatton]

As far as I can see, The circuit starts with Q67 on, Q65 is off until C102 charges, Q66 is off because of no current from Q65. the -15v must be sourced from elsewhere.

Once C102 charges, Q65 will turn on, turning on Q66 too, because Q67 is on, so the mute line goes high. Anything turning off Q67, ie TH1 closing, will turn off Q66 too, allowing the mute line to drop.

I hope that helps

[Enzo]

Ot has its own little supply, is C99 charged up to something respectable? And is timing cap C102 OK? Q66 is the mute transistor but it is in turn controlled by Q67 with D97 along for the ride. Check them all.

And check the voltages through that little circuit. You need to isolate the problem. Is the control circuit working but can't turn on Q66? Or is the circuit working and it is purposely muting for some other reason - for example a stuck thermal cutout.

And you only show a small part of the schematic. We have no way of knowing if the -15v is coming from the amp circuit somewhere rather than through Q66.