No channel switch....unless Reverb is active

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Toalpo

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Hi!!

I have an Express 5:50 and a disturbing problem. I can not switch from ch2 to ch1 with the footswitch unless Reverb is on in the footswitch. If reverb is off in the footswitch the LED changes when pressing channels but it doesnt change anything in the amp. If I disconnect the footswith I can change channels with the little switch in the front.

I also have notice like if the reverb is not to intense, actually in ch2 is really weak. I have open the footswitch and review connections, and looks fine so I guess the problem is in the amp. Anyone got a problem alike? any suggestions? thank you!!
 
The reverb is tube driven so it is always worth it to check that. See is any of the tubes are bad or not seated properly. The switching problem could be a bad MIDI cable, a bad footswitch, or a loose MIDI connection. It's not a standard MIDI cable so its not likely that you have a replacement although I suppose you might. Try flipping the cable around and maybe tightening up the connector on the footswitch a bit. It has been known to come loose. Mesa has a simple fix for this- might be on their website,
 
Thank you Len for ur reply. I check the cable and change the reberv tube with no success. I realise that when reverb pin is grounded it uneables to change channels. So I decide to check the schematic of the amp to find out why. It makes sense because CH2 is selected by grounding pin 4, but reverb is selected by pin 5 so there should be a short somewhere.

I took apart the amp and follow ckt traces to find out pin4 trace and pin5 trace where shorted in the back channel jack :shock: just to foll around I plug a jack and the short dissapear!!

I am going to clean those jacks and the board just to make sure the short was just some dirt, not sure yet. Now the footswith is working perfectly. I will let you know if definetly was some blur or dirt in the jack.
 

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