Hi. I have a Mesa Nomad 55 amp that's giving me trouble, and I was wondering if anyone here would be willing to help me track down the problem.
I recorded a video that shows what's happening, but I'll try to explain here, as I don't know how to share the video.
All 3 channels work. Master volumes and gain controls work. Lights come on, and the voicing switch on each channel works.
However, none of the tone controls works. On channel 1, if I rotate the treble control down to around 8:00, the amp suddenly gets loud. One other control does a similar thing at around 3:00. I think it's the mid on channel 2.
Anyway, I'd like to get these tone controls working. I'm thinking that since all 3 channels are affected, it's something in the circuit where everything's combined, and maybe the whole tone stack is open or grounded, but I can't find the problem. The board shows no signs of overheating, nor do any components, and there is no evidence of abuse. While I see what look like many "cold" solder joints from the factory, I can't find any cracked or loose connections.
Wondering if anyone can give me some clues on where to test.
I recorded a video that shows what's happening, but I'll try to explain here, as I don't know how to share the video.
All 3 channels work. Master volumes and gain controls work. Lights come on, and the voicing switch on each channel works.
However, none of the tone controls works. On channel 1, if I rotate the treble control down to around 8:00, the amp suddenly gets loud. One other control does a similar thing at around 3:00. I think it's the mid on channel 2.
Anyway, I'd like to get these tone controls working. I'm thinking that since all 3 channels are affected, it's something in the circuit where everything's combined, and maybe the whole tone stack is open or grounded, but I can't find the problem. The board shows no signs of overheating, nor do any components, and there is no evidence of abuse. While I see what look like many "cold" solder joints from the factory, I can't find any cracked or loose connections.
Wondering if anyone can give me some clues on where to test.
Yes. I have the common ones online and from the Mesa website. Can you point me to any likely parts to check on?
Looks like the reverb is also not working now, but when I thump the amp, it makes a noise, so I'm going to review the reverb postings I saw on here to see if any of them have complete information.
Looks like the reverb is also not working now, but when I thump the amp, it makes a noise, so I'm going to review the reverb postings I saw on here to see if any of them have complete information.
Is this one of the amps with the controls on the panel having little 3-4 inch wires back to the board? Little 16mm controls.
Do any of the controls feel a bit loose?
In servicing these things I found the pots often came loose. If something pushes against the knob. Like in transit or if your guitar falls against the controls. Pushing on the knob shoves the shaft against the rear of the control, which partially springs that cover. The pot cover is held to the bushing part by four small tabs bent over. If they are no longer flat against the bushing body, your cover is loose. And the cover is what holds the wiper assembly in good contact with the resistive element.
If this turns out to be the case, simply use pliers to squeeze the tabs back down tight.
I could be wrong, but memory tells me Nomads and Heartbreakers were in this era of amps.
Do any of the controls feel a bit loose?
In servicing these things I found the pots often came loose. If something pushes against the knob. Like in transit or if your guitar falls against the controls. Pushing on the knob shoves the shaft against the rear of the control, which partially springs that cover. The pot cover is held to the bushing part by four small tabs bent over. If they are no longer flat against the bushing body, your cover is loose. And the cover is what holds the wiper assembly in good contact with the resistive element.
If this turns out to be the case, simply use pliers to squeeze the tabs back down tight.
I could be wrong, but memory tells me Nomads and Heartbreakers were in this era of amps.
Hi. Yes. I read some other posts about this issue (not sure if they were from you), and this weekend, while I was removing and inspecting all the pots, I did find that many were loose, and I tightened and cleaned them all. I discovered that although they all tested normal, some must have not been making a connection, because after reinstalling them all, the tone controls are now working normally. Seems like such a strange pot design, though it does reduce weight. The wiring method eliminates all the cracked solder joints on the board that other amps suffer, but this system offers it's own issues.
I still can't get the reverb to work yet. I tested the tank in another amp, and it works fine. I seem to have continuity in the cables, and I have cleaned and tightened all the contacts. When I thump on the tank, I can hear the springs rattle through the amp, so I'm guessing the return is working. I'm guessing all this means I have a failed part or bad solder joint on the board. Not sure what to test first, though. Any recommendations?
I still can't get the reverb to work yet. I tested the tank in another amp, and it works fine. I seem to have continuity in the cables, and I have cleaned and tightened all the contacts. When I thump on the tank, I can hear the springs rattle through the amp, so I'm guessing the return is working. I'm guessing all this means I have a failed part or bad solder joint on the board. Not sure what to test first, though. Any recommendations?
I'm not an expert on this amp, but you've already cleared away much of the fog. The schematic suggests several likely culprits, e.g. RY1('b' contacts) controls the reverb tank drive signal. Is there signal at the relay; is it being energized to select the correct channel; does selecting ch1 differ from ch2/3? The relays are a likely bet by my experience, but if you have to go back a layer to the circuits controlling the relays, it'll get a little more complicated.
Good Luck
Cheers
Good Luck
Cheers
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