Need help diagnosing Mark V problem

PhilipR · Jun 7, 2010

I've had my Mark V for about a month. After moving it across the room it now doesn't produce any sound on any channel.

All the lights and channel switching work fine.

Switching between solid state and tube rectifier makes no difference.

Switching between wattage modes on all channels makes not difference.

All 4 power tubes illuminate. The rectifier tube doesn't appear to light.

My diagnosis: rectifier tube, although I am puzzled why the SS rectifier option doesn't fix this.

Thanks so much for your help!

RocknRory · Jun 7, 2010

Hmm. I'm no amp repair expert but it shouldn't be the rectifier tube because you can always switch to solid state rectification and that bypasses the tube. This sounds like a fuse mightve blown or a preamp tube isn't working. You said all three channels don't produce sound? V1 might be dead. Try removing 2 powertubes with a cloth and swapping the preamp tubes around. The Mark V manual will tell you which preamp tube is V1 and whatnot. The best method is to flip the amp upside down (unplug it first!) and take the tube cover off of the preamp tube and wiggle the preamp tube out. Hope this helps. If all else fails just call Mesa and tell them whats wrong, they can give you much better troubleshooting than I can.

eudaimonia02912 · Jun 7, 2010

I've heard from others, though I can't say whether this is true, that even with the tube rectifier switched off, it is still in the circuit, and a bad tube there will cause the amp to fail.

domct203 · Jun 7, 2010

If the amp is on (lights etc) it is not a fuse problem.

Yes the rect tubes are always in the circuit but if the fuse is good chances are so are the tubes.

If it's a preamp tube, V1 effects all channels.

Check your speaker cable. Is it all the way into the jacks? Check it with an ohm meter or another amp to make sure it did not fail.

Hard bypass the loop.

Is the solo knob pulled and the amp in mute?

Check your guitar cables also.

Good luck.

Dom

phyrexia · Jun 7, 2010

Is guitar plugged in with good, tested instrument cable? Is speaker plugged into amp with good, tested speaker cable? (Silly questions, I know, but always best to start at the bottom.)

Are you using the footswitch or are you changing channels with the knob on the back? My knob on the back was in between two positions once and it didn't make any noise. (Sounds like you're switching between channels successfully.

Do you hear a pop from the amp's speaker when switching from 45w to 90w?

The rectifier tube can blow without the fuse blowing. Modern rectifier tubes are not very hardy.

Make sure you're not tuner muted/pull output muted.

boogieman60 · Jun 7, 2010

I broke mine on a gig last month...so I took it out....amp worked but balance was all messed up...used a backup.. I removed the footswitch pouch from the inside of the amp...Thats how I broke the rectifier...I suspect a lot of tube problems are related to that problem. Its just to tight to get that footswitch out of that spot. Hit the tubes every time....now mine are fine...

PS the tube is always in the curcuit..