Mark V 25 seems dead

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opauly

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Apr 4, 2019
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Hello!

It turns out my Mark 5 25 head has no working front panel. All tubes are OK, power transformer is OK, fuse is OK, but there is no pilot light on and there is no sound. It is basically dead. Power tubes are being fed since they glow and get very hot, preamp tubes are not that hot but they are being heated. Also, the internal fan is not turning on.

Do you have any hint on what could be going on?
 
It turns out that the output of the LM2940 was providing 0v, but the IC was OK. I desoldered that pin and the +12V supply was fine. Had to trace the problem to C54, a 15uF capacitor that went bad. Replaced it, and the amp is back!

Thanks for the help!
 
Awesome

Its good to know it was not much that went wrong in the scheme of things

Casey
 
Great that you were able to do it yourself. I have built a couple of tweed clones and done some mods on them but wouldn’t trust myself to dig in to my MV.
 
Well I am an EE and have worked with pedals, guitars and amps for a while now. But working with amps is always dangerous! Glad to know this forum is one of the best resources out there right now.

Keep on rocking guys!
 

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