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Mesa Mark V Intermittent Issue

iggs

Member
Messages
2,616
Hey all, just wondering if anyone has experienced an issue like this before and can offer some insight on what could be the problem.

The amp was bought new 5yrs ago and has been working perfectly until about a year or so ago when it developed an intermittent power issue. It will randomly flicker on/off for no reason ... please see video below.

- tubes were checked and replaced
- fuse was checked and replaced
- power cord was checked
- amp was looked over by an authorized Mesa tech and could not find anything wrong
- according to the tech 12v rectifier diodes are fine (common issue with these amps)
- Mesa support wasn't very helpful and said it has to be something with the power supplied
- wall outlet is fine and power in the house is fine, amp worked properly before
- none of my other amps, pedalboards, studio gear ... etc. have any similar power issues
- issue happens with or without the footswitch
- issue happens with or without any signal going into the amp
- issue happens regardless of any amp settings or channel selection

Any help or info is greatly appreciated! Thanks in advance!

 

iggs

Member
Messages
2,616
Have you tried using the amp without the supplied Mesa pedalboard ?
Might be the pedalboard is somehow causing the problem.
If by pedalboard you mean footswitch then yes, tried with and without, no difference.
 

blackba

Gold Supporting Member
Messages
11,030
These type of issues can be the hardest to figure out. If it were on my bench I would Take a wooden drum stick and start poking around in the chassis looking for a loose connection or cold solder joint.

If you want to keep it in the chassis, try tapping on the amp in various places and see if you can find a weak spot.

How often does it act up?
 

iggs

Member
Messages
2,616
I had basically the same problem, from what I read it's to do with the diodes in the power supply section. There are a few similar threads on the Boogie forum that might help:
- https://forum.grailtone.com/viewtopic.php?f=33&t=74584
- https://forum.grailtone.com/viewtopic.php?f=33&t=84989
- http://forum.grailtone.com/viewtopic.php?f=33&t=70633

I had it fixed by a Mesa tech under warranty.
Right ... the tech I took the amp to said diodes were fine. I may take it to another place and have them look it over once more.
 

iggs

Member
Messages
2,616
These type of issues can be the hardest to figure out. If it were on my bench I would Take a wooden drum stick and start poking around in the chassis looking for a loose connection or cold solder joint.

If you want to keep it in the chassis, try tapping on the amp in various places and see if you can find a weak spot.

How often does it act up?
The tech mentioned he did the “hammer test” and there was no change. I tried moving the amp around and tapping it with hands but could not reproduce the issue. I also wiggled power and standby switches but again nothing.

It acts up almost every time I turn it on, but sometimes it flickers right away and sometimes after being turned on for 45 min. No rhyme or reason.
 

guitarchitect

Gold Supporting Member
Messages
280
Mine had the same problem. Eventually it froze in the off state. Bad diodes. I replaced them on the board myself and it has been rock steady since. There is a tech bulletin I found from the Boogie board that guided me.
 

IanRubbish

Member
Messages
388
I brought my Mark V to an authorized tech and it still had issues. Went to Petaluma and it spent 1 hour on the bench and cost 160 to fix, it's now perfect again.
 

guitarchitect

Gold Supporting Member
Messages
280
The OPs video looks the same as what my Mk5 90 was doing. The power section is not affected. The 12v circuits are cutting out because of a quad of diodes that have a tendency to fail intermittently. In my case, eventually the bad one failed permanently, so my amp was stuck in the failed mode. The power tubes still powered up, but all 12v dependent sub-circuits like channel switching, front panel lights, fan, and any sound were cut off. I didn’t check, but I would assume the preamp tubes were not powering up.

Replacing the diodes was somewhat tricky as they are in a tight location. But its doable. An amp tech or Mesa would be the safest bet. I took a chance on my own skills, the amp being well out of warranty, and was successful. I ordered replacement diodes from DigiKey. I have all the info and can post it if it would help the OP.
 

fallingman16

Member
Messages
224
The OPs video looks the same as what my Mk5 90 was doing. The power section is not affected. The 12v circuits are cutting out because of a quad of diodes that have a tendency to fail intermittently. In my case, eventually the bad one failed permanently, so my amp was stuck in the failed mode. The power tubes still powered up, but all 12v dependent sub-circuits like channel switching, front panel lights, fan, and any sound were cut off. I didn’t check, but I would assume the preamp tubes were not powering up.

Replacing the diodes was somewhat tricky as they are in a tight location. But its doable. An amp tech or Mesa would be the safest bet. I took a chance on my own skills, the amp being well out of warranty, and was successful. I ordered replacement diodes from DigiKey. I have all the info and can post it if it would help the OP.
The OPs video looks the same as what my Mk5 90 was doing. The power section is not affected. The 12v circuits are cutting out because of a quad of diodes that have a tendency to fail intermittently. In my case, eventually the bad one failed permanently, so my amp was stuck in the failed mode. The power tubes still powered up, but all 12v dependent sub-circuits like channel switching, front panel lights, fan, and any sound were cut off. I didn’t check, but I would assume the preamp tubes were not powering up.

Replacing the diodes was somewhat tricky as they are in a tight location. But its doable. An amp tech or Mesa would be the safest bet. I took a chance on my own skills, the amp being well out of warranty, and was successful. I ordered replacement diodes from DigiKey. I have all the info and can post it if it would help the OP.
Post that info please, could help lots of MV owners in the future
 

eigentone

Gold Supporting Member
Messages
7,357
I have this issue with my Mark V head as well. I bought it new and the issue began happening sporadically around 4 years in but I reached out to Mesa sometime after 5 years after I had tried the usual suspects. I have spent hours testing different tubes, testing without the footswitch, seeing if there is a correlation to all power, etc. It can be hard to reproduce. It's not my main amp so it's just not been getting much use in the past year. It used to be kind of rare but now it is pretty predictable and unusable when it happens regularly.

I wrote them in May:
Hi there. My Mark V has an issue where it shuts off momentarily and then comes on again a second later. Sound drops out, there are numerous clicks (relays?), lights go out and it comes back but it is usually reinitialized (when the footswitch is connected.) I also tried this with the fooswitch disconnected (reproduced.) And I tried this with another set of power tubes and rectifier (reproduced.)​
Any idea what could be causing this issue?​

Mesa responded in under 5 minutes, which was pretty awesome:
Is the AC cable firmly seated in the AC jack on the amp? If yes, check for any play with the fuse cap. If the fuse cap is not intermittent - it could be related to your line voltage, or it could be an issue with the Low Voltage power supply - which is rare but possible.​
Please let me know if you have any questions or need assistance in any way. Thanks!​

I just checked and my tech is an authorized repair center so I think that will be my next step. I have spent too much time trying to hunt this down. But I am following this thread now.
 

blackba

Gold Supporting Member
Messages
11,030
The OPs video looks the same as what my Mk5 90 was doing. The power section is not affected. The 12v circuits are cutting out because of a quad of diodes that have a tendency to fail intermittently. In my case, eventually the bad one failed permanently, so my amp was stuck in the failed mode. The power tubes still powered up, but all 12v dependent sub-circuits like channel switching, front panel lights, fan, and any sound were cut off. I didn’t check, but I would assume the preamp tubes were not powering up.

Replacing the diodes was somewhat tricky as they are in a tight location. But its doable. An amp tech or Mesa would be the safest bet. I took a chance on my own skills, the amp being well out of warranty, and was successful. I ordered replacement diodes from DigiKey. I have all the info and can post it if it would help the OP.
Great info, so do you know if you are replacing the diodes with the same specs that were in there, which would indicate Mesa got a bad batch? Or when you replaced them are you putting in diodes with higher ratings?
 

guitarchitect

Gold Supporting Member
Messages
280
Great info, so do you know if you are replacing the diodes with the same specs that were in there, which would indicate Mesa got a bad batch? Or when you replaced them are you putting in diodes with higher ratings?
See the tech bulletin I posted above. It specifies a different diode as a replacement, so I assume that’s a beefier or higher rated part.

I do think it’s a rare problem. My amp has a higher serial number than indicated in the tech bulletin. But it definitely had the problem. I play at least a little every day, and the amp would start cutting out randomly three or four times a week. I replaced the diodes about six months ago and it has been flawless since.
 




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