Hey guys. New to the board but from what I've read you guys know your stuff and nice to boot! Bravo. So the reason I'm here is my buddy had a dual rec solo head that had a few issues. From what I've been told is that he used the amp a while back into a cab that apparently had a bum jack. He was getting no sound and for whatever reason he left the amp on fir another hour. I liked at it and he had burnt diodes in the preamp board so i changed those. I plugged it back in after testing circuits and i still get no sound out of channel 1 and some out of 2. I turned it off before running anything else. He also mentioned that previous to the no sound issue he was having trouble with the solo function sticking on. Amy suggestions? It is no longer under warranty and he left it with a tech who took 8 months to say it had burnt diodes but couldn't get to it...lol maybe he knew there was a lot wrong 't with it? Iol. Thanks guys!
Dial rec solo issue
- Thread starter Wavey63
- Start date
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Welcome to the forum.Wavey63 said:
I'm guessing you were trying to tell us that "he left the amp on for another hour"?
Have you ruled out bad tubes yet? If he tried to play the amp for an hour without a proper speaker load the output tubes are most likely damaged, and possibly the output transformer as well.
I would bring the amp to a Mesa certified tech, they are listed on Mesa's website.
Good luck,
Dom
Have you eliminated the power tubes as the failure?Wavey63 said:
Can you get a signal from the FX loop send?
Dom
Finally got time to look into the amp a bit more. One thing i find questionable is the 2 yellow leafs from the PT that are speed to read at 3vac according to the scheme. One reads at 4.5 and the other 0vac. Is this a bad PT? Should i treat those leads out of the circuit?
Could you translate this?Wavey63 said:
There should be three sets of secondary taps from the PT, B+ at approx. 350V, 5V for the 5U4GB heaters, and 6.3V for the preamp tube heaters, switching & pilot lamp.
http://www.freeinfosociety.com/electronics/schemview.php?id=507
I think you are measuring the 5V rectifier tube heater taps. Could you share some pictures?
Dom
Have you rules out bad tubes yet?
Have you tried sending a signal into the FX return to see if you get sound?
If you suspect the 5U4GB filament supply, remove those tubes and run the amp on silicon diode rectification until you sort out the other issues you have with passing signal.
One thing at a time.
Dom
Have you tried sending a signal into the FX return to see if you get sound?
If you suspect the 5U4GB filament supply, remove those tubes and run the amp on silicon diode rectification until you sort out the other issues you have with passing signal.
One thing at a time.
Dom
LOL Siddhartha.Wavey63 said:
If you are not getting signal through the amp, and you have completely eliminated all tubes as an issue, you need to determine if this is preamp or poweramp. Pretty basic stuff. First thing I would do is plug a guitar into the amp, then connect the FX send to the FX return of a working amp and see if you get signal. If yes then you know the issue is not in the preamp. Next you would send audio into the return of the suspect amp, either from another amps FX send, or even an MP3 player to see if it passes audio to the speakers.
BTW- if you look at the schematic for the power supply you will see that the 5U4GB tubes are always in the circuit regardless of the rectifier select switch. This is why I recommended pulling the tubes and selecting diodes. If there is an issue with that TX secondary it could be pulling down other voltages.
Dom
deeman
Well-known member
I had a Dr. named Siddhartha.
Ok so I was testing the amp with the fx loop as you recommended... get this. The amp works perfectly once there is something plugged into either the send or return on the mesa and another amp. Once I unplug the cord from either the mesa or the other amp it goes dead. Well not totally dead. I can hear very faint sound from the mesa cab and also the bias led goes out ounce the loop is unplugged. Any suggestions?
I haven't looked at the schematic yet but in my mound it seems like it may be a ground issue in the loop circuit? Another symptom is that the mesa will not work unless the other ano is plugged into the power outlet regardless of whether it's on or not. So I'm thinking that with the other amp plugged in that com6petes a ground that is needed to make the mesa work correctly?
Your main electrical ground is made at the chassis, usually on a lug on the PT mounting bolt. Do you have continuity from that point to the ground lug on the power cable?
