Power supply repair

Just a quick note to share some strange symptoms and what resolved them. I have a Mark V combo that started to do something strange every time I practiced. The amp would pop and then sometimes reset back to the startup (all channel lights on) or the pilot lights would flicker off and then back on. No lightning or other bad sounds other then the fairly loud pop. I replaced the rect/power tubes (they were due anyway) thinking that was it. No joy. Note, this did this mainly at low/bedroom vols, at gig or band volume, this never happened.

Last week, the amp was in standby and I was about to play when it switched itself off. The tube heaters were still on so I knew it wasn't a fuse or something similar. Discussions with Mesa confirmed that it sounded like the low voltage power supply diodes (12V). Took it to a local shop (Slemmons in Dallas is awesome BTW) and they replaced the rectifier diodes in the supply. Turned it around in 2 days and thanks to the Mesa warranty, just about as painless as possible.

Not sure if this is common or rare, just thought I'd share it.

Good to know! Thanks!!!

Something else that is curious, since this repair, I never get the dreaded relay chatter when coming out of standby. Didn't happen all the time but now it is totally calm when switching out of standby. Might be related?

theredmenace said:

The amp would pop and then sometimes reset back to the startup (all channel lights on) or the pilot lights would flicker off and then back on

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Mines developed a similar bug, but i cannot track it down to the amp or something in the house thats interfering with the switching.
it only does it once with in 2mins on initial start up but not every time and doesn't cause any problems for the rest of my practice sesh

weird :? :?:

Mines developed a similar bug, but i cannot track it down to the amp or something in the house thats interfering with the switching.
it only does it once with in 2mins on initial start up but not every time and doesn't cause any problems for the rest of my practice sesh

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That was my experience too. Seemed to be worse at my place (rarely at practice) but it was concerning since we had a few rare opps to play out and I was concerned it would do that during a show. Never did. Was hoping it was foot switch issue or bad AC. In addition to the relay chatter, I would sometime hear strange noise in the preamp (ch. 1 mostly) almost like faint radio interference. Mostly when the amp was less than a few minutes off of standby. Would go away eventually.

Eventually the diodes in the 12V supply gave up and it would not power up. After the repair (yea warranties), these issues have gone away. Super quiet operation and no chatter ever. Seems to be a rare condition but if yours gets worse, you might check with Boogie. Best of luck.

theredmenace said:

eventually the diodes in the 12V supply gave up and it would not power up. After the repair (yea warranties), these issues have gone away. Super quiet operation and no chatter ever. Seems to be a rare condition but if yours gets worse, you might check with Boogie. Best of luck.

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thanks for the info, Ive spoken to the mesa importers here in OZ and in turn a few "near by" repairers one said it could be all the JFETs in the amp and the other suggested that our AC was the problem, seems that one of them is now closing his doors on amp repairs and the other didn't even have a reference schematic to discuss the 12v circuit with me... seems like a rare problem.

i might just crack it open and replace the N1007's in there as a precaution, is it possible to speak to your tech from me to confirm it was just the DIODES?
as i might have a few n1007s in my spares bin that i can put in this weekend

all the best

I had the same problem for a while and the other day I turned it on and it looked like it was off -- no LEDs channel switching, no fan etc. -- but there was a little hum in the speaker which increased as I turned up the Output. It also looked like the tubes were all on.

Well after a bit of research (including this thread) and a little testing, I found that the culprit was the 4007 diodes D16,D17,D18,D19. They're located on either side of the brown tap of the Power Transformer and they feed the heaters to V1,V2, and V5 as well as the fan and apparently the LEDS and switching. I then noticed that while though all the tubes were on, V1,2, and 5 were actually not. I took it to a friend who's an amp tech and he replaced the 4 diodes and now everything works fine.

Thanks to the OP for sharing, this definitely helped me figure things and I thought I'd add my experience for anyone else who runs into this.

i have this issue,too in China.
i unplug the foot switch, 2days no happen again.
i replace the 5u4g at first but it keeps happen. so move out the foot switch.