Dual Rectifier Failure appears to be rare (now resolved!!!)

[jshutchins28]

Hi everyone, I have tried doing a lot of searching on my issue, however I am coming up nill, so hopefully someone out there can point me in the right direction. I have a Mesa Dual Recto, I bought it brand new almost 12 years ago. Aside from normal re-tubing I have had zero issues with my head, its been a fantastic road warrior. With that said I am not new to these amps. A failure has recently started to occur intermittently however. When I turn on the amp, everything powers on EXCEPT the channels. Those familiar with the dual know that when you flip on the power switch you get a "click" noise when the orange channel two lights up. Well this doesn't happen all the time now. The first time it happened, I turned the amp off, and then back on and it worked again. I took it to an authroized mesa repair facility and they could not get the amp to fail while there for a week, so they could not troubleshoot the issue. When I explained that the amp powers on but the channels do not turn on they looked at me dumbfounded. This was a few weeks ago, and I had many performances and the amp worked flawlessly. Well this past weekend, while setting up for a gig, I turned on the amp and everything powered up normal. As I was setting up my microphone the channel 2 light just turned off, and now the channels will not come back on when you turn the amp off, then on again. I am hoping that whatever part, or issue doesn't work is actually dead so it can be fixed. If anyone has experienced this issue, and can point me in a direction to go so I can point the repair guys in the right direction I would appreciate it. I sent a message to mesa corporate as well, but its a holiday weekend and I wont hear from them till probably the end of the week, I have a really big gig coming up in 2 weeks and filming as well, so I hope I can get this sorted prior, otherwise I have to go buy another amp while this is sitting in the shop! Thank you for your time!

 

[screamingdaisy]

Do you get any sound through the amp when this happens? Can you still change channels using the footswitch? If you disconnect the footswitch can you switch channels using the control in the rear?

 

[afu]

If the issue was intermittent, affected the relay (click sound) and affected the indicator lights, I would think the problem is in the switching circuit. For a relay to close, a ground connection needs to be established. When another channel is selected, the ground connection is made for it and the former channel's ground is lifted. Since the problem affects all channels, the fault could be somewhere in which all the individual circuits meet for ground or power, or a connection to a component between those areas and all channel relays.

Look for corrosion, disconnection, or a bad solder joint in one of those few areas. While it could be a component failure, solid state components tend to just fail and kill operation. A poor connection would be more likely to be intermittent.

 

[deeman]

Any news? Was it the footswitch?

 

[jshutchins28]

Hey all thanks for your input, the amp is fixed, Mesa got back to me via email very quickly and my tech which is authorized mesa knew the tech who emailed me. Long story short the amp stayed dead this time when it was on the bench. It turns out one of the rectifier circuit diodes finally gave up in the +- 3v power supply. 2 dollar part, and an hour of "extremely concentrated" labor according to the tech because he said you pretty much needed micro hands to fix it. I am picking it up today and my tech said it turns on and plays perfectly now. He said that with time these things just tend to fail, but I should be good to go for a long long time now. Which is good because my gig schedule keeps getting piled on! Thanks again everyone!

Jon

 

[jbird]

Did you ever try running your tube rectifiers to solve this?

 

[bandit2013]

A small signal diode? 3volt supply, I would have thought the switching logic used 5V which I believe is the case for most of the other amps Mesa has designed. Good to hear you got it fixed.

 

[afu]

Did you ever try running your tube rectifiers to solve this?

The 3 V supply is rectified from the heater taps. There're diodes and filtering after the heaters to supply the switching circuits.