Mesa boogie dual rectifier multi-watt problems

[Rod]

Hello!

I have serious problems with this mesa, tryed to contact mesa and not a single answer. With this attitude from Mesa, i will never ever buy again a mesa boogie amp.

I know about amp electronics, not a expert level, but i can solve some problems. I have some tools, that can help me sort out this problem and in this forum i have found the attached schematic.
So i need you amp gurus to solve this problems, in advance i thank for you help.

The problems are the folowing:

1- The amp clean is not clean anymore, its like a distortion channel
2- When im playing the amp, for 2 seconds the amp mutes, during this time the amp has no sound, the light that indicates the activated channel and turns off.
3- when selecting channels the makes a loud pop.

It seems that the problem here is the mute circuit from the schematic i have attached, but i have no ideia what could be doing the clean to distort, so can someone tell me what start to check and what componentes to replace?

[Rod]

i read somewhere that this can be JFET problem

[Pedro Vecino]

The scheme you have put is that of the old model (not multi-watt).
Sometimes the group of four power diodes for the switching circuit fails. At least in the old model, due to overheating / degradation of the printed circuit in that area.
You should check what happens in those two seconds: if no LED responds to the channel change or if it recovers when changing the channel.
In many cases a distortion is detected only on the clean channel of an amplifier when it is general (common for all channels). Keep it in mind.

[Rod]

Hello Pedro, the clean channel was clean and now is not anymore.

The loud pop when switching channels seems to me that are the JFETs j175, because they job is to prevent this popping.

The amp recovers is sound and channel light indicator, after the 2 seconds muted and deactivated light that indicates the activated channel. So this seems somekind of problem in the mutted circuit.

The scheme you have put is that of the old model (not multi-watt).
Sometimes the group of four power diodes for the switching circuit fails. At least in the old model, due to overheating / degradation of the printed circuit in that area.
You should check what happens in those two seconds: if no LED responds to the channel change or if it recovers when changing the channel.
In many cases a distortion is detected only on the clean channel of an amplifier when it is general (common for all channels). Keep it in mind.

[FerNax]

Sorry to revive this post but I'm having the same exact issue with my multi-watt dual rectifier, I don't really care about the popping, what concerns me the most is this issue I have where my amp suddenly stops producing sound and the channel led's turns off, it all happens in just a millisecond and then it gets back to normal (when it happens a sound similar to the "changing channel sound" can be heard. I used to have the issue quite frequently and then I realized I was not using a proper speaker cable when I get a real speaker cable the issue disappeared for a few months but now, all of a sudden, it came back with no apparent reason. I'm thinking maybe it's the cabinet because this never happened to me with my torpedo captor load box, could that be possible? Could the cabinet or the speakers be responsible for this "cutting sound" issue? maybe the wiring is faulty and then the internal protection system of the amps turns it off when no impedance is found?
Thank you very much.

[clintronics]

Fernax, Is the amp on top of your cabinet when it drops out? seperate the two so the vibrations dont affect the amp. if it only screws up on top of the cabinet could be bad solder joint/ cracked wire.

[htrd]

A friend of mine had a similar problem with his 3-channel Dual Recto with sudden mutes and turned off leds. It was due to the bad rectifier in the V1 heater circuit and dying V1 tube. Switching relays are powered by the same DC node.

[FerNax]

Fernax, Is the amp on top of your cabinet when it drops out? seperate the two so the vibrations dont affect the amp. if it only screws up on top of the cabinet could be bad solder joint/ cracked wire.

Hey there! thank you so much for aswering, it's a good guess and yes, it happened to be on top of my cabinet always that this issue occurred, but I really doubt that's the cause for this issue because it also happened with the amp not being played at all (just turned ON).

[FerNax]

A friend of mine had a similar problem with his 3-channel Dual Recto with sudden mutes and turned off leds. It was due to the bad rectifier in the V1 heater circuit and dying V1 tube. Switching relays are powered by the same DC node.

Thanks for taking the time to answer, oh I see, hope that's not my case, I'll have to send it to an amp tech to see if there's any solution, at this point I'm just clueless I changed everything (cables/cabinet connections/cabinet itself) hoping the issue was not within the amp but I'm afraid that that's the case. What really bugs me is that this is totally random, it may not do it for weeks and then it suddenly happens, if any circuit happens to be faulty wouldn't it be failing constantly?

[htrd]

if any circuit happens to be faulty wouldn't it be failing constantly?

In the case of my friend the sudden mutes were random and usually after 1-2 hours of active work, overheating, I suppose. He is very lazy and waited for years until the amp ultimately failed, shorting the V1 heaters and burning the diodes.
Maybe you have bad solder joint somewhere in this circuit.

[FerNax]

Hey there to everybody! Just wanted to make a quick update about my case. It turns out that the issue was in my house's electric connection, luckily there was nothing wrong with the amp. Seems like the DR, due to its complex switching system, is really susceptible to electric line issues and ground/voltage problems really make them behave weird. To everyone having the same issue, please review your electrical connections! you may save tons of money and tons of stress as well lol
By the way, thanks to everyone that took some time to leave an answer, I appreciate it.