Crate gtx65

[jbmdisco]

I have crate gtx65 at moment. Ocassionaly the output goes dc. Disconnecting the speaker and reconnecting 'resets' amp and works 1st class for period of time. Switch off and on goes dc again but not every time.
No dry joints and all caps diodes res meter out fine. Any pearls of wisdom available?

[Jazz P Bass]

Can you post the schematic?

[mozwell]

Circuit attached
When the output goes to DC, measure the power supplies, TP14 & TP15 as well as at the various places in the power amp (across C45 & C51), make sure one of the power supplies is not collapsing.
Check the +/-15V power supplies as well.
Also measure across R48, if we have DC here, then the power amp is ok & we need to remove the DC offset from the input of the power amp
Maybe temporarily remove D14 & D17 to disable the current limit & see if that is the problem
Also try removing the mute jfet Q16, we may be getting DC "injected" into the power amp input if the transistor is faulty. It may be worth adding a 12V zener from gate of Q16 to 0V to protect the gate... its driven from 40V through the resistor divider of R52 & R56 on some versions of the amp

[jbmdisco]

Thanks for the replies.
Since I posted the initial thread I have switched the amp on, on a daily basis, in a corner of the workshop and it has failed to fault. I have allowed a guitarist to drive the life out of it several times with no issue but I am still hesitant to return to owner for time being. I will continue to monitor the performance for another few days.
This is the 3rd Crate amp that has attempted to elude me to date.