MesaMad1378
Well-known member
Hi there all, well I had a problem with my 2:90 blue light, when I received it (before the voltage mod), thought I'd share what I did to repair it.
I was playing for about 3 or so minutes then I heard a pop and one of the cabs cut out. I checked the output fuses straight away and found the b channel fuse blown. I went and got some fuses, 1amp 3ag, and put it in, turned it on, waited for a minute for tubes to warm up, then flicked it from standby. I watched the tubes and immediately the top 2 on the b channel started to glow. I suspected the tubes were gone. I drove down to the guitar store, got 2 matched sets of Mesa 6L6 tubes (yellow, it had blue in it). I drove back and fitted them to the outer ( a class) positions, turned it on, let it warm up, flicked it off standby, watched tubes, same thing.
I got hold of a good, legible, schematic and proceeded to go through it trying to nut out what the problem was. I did some tests etc all over the board comparing readings and found the grid no.2 voltages, pin 4, on the top 2 tubes were not at around the -50vdc like the rest. I pulled all the tubes out and looked at all the sockets, some were stretched, maybe not connecting to tube pins properly. I closed them up so they were all tighter, refitted tubes, still no good. I tested resistors all around and couldn't get a good reading on R363(equivalent of R362, I think) which was 82k. So I sourced anothe resistor and changed it out, still no go. Tested the resistor, it tested fine. I went through the schematic again, did more tests. I came to the conclusion that the orange drop C20 (equivalent to C22, I think) was the culprit. I removed it and tested it. Orange drop shagged. I sourced some new orange drops, fitted and tested. Here goes, connected, tested all good, turned it up and away she went.
So what I think happened was during travels, the tube pins had stretched the sockets, therefore not connecting to the tubes properly, causing the capacitor to blow.
Any thoughts, please feel free to add
Cheers Brett
I was playing for about 3 or so minutes then I heard a pop and one of the cabs cut out. I checked the output fuses straight away and found the b channel fuse blown. I went and got some fuses, 1amp 3ag, and put it in, turned it on, waited for a minute for tubes to warm up, then flicked it from standby. I watched the tubes and immediately the top 2 on the b channel started to glow. I suspected the tubes were gone. I drove down to the guitar store, got 2 matched sets of Mesa 6L6 tubes (yellow, it had blue in it). I drove back and fitted them to the outer ( a class) positions, turned it on, let it warm up, flicked it off standby, watched tubes, same thing.
I got hold of a good, legible, schematic and proceeded to go through it trying to nut out what the problem was. I did some tests etc all over the board comparing readings and found the grid no.2 voltages, pin 4, on the top 2 tubes were not at around the -50vdc like the rest. I pulled all the tubes out and looked at all the sockets, some were stretched, maybe not connecting to tube pins properly. I closed them up so they were all tighter, refitted tubes, still no good. I tested resistors all around and couldn't get a good reading on R363(equivalent of R362, I think) which was 82k. So I sourced anothe resistor and changed it out, still no go. Tested the resistor, it tested fine. I went through the schematic again, did more tests. I came to the conclusion that the orange drop C20 (equivalent to C22, I think) was the culprit. I removed it and tested it. Orange drop shagged. I sourced some new orange drops, fitted and tested. Here goes, connected, tested all good, turned it up and away she went.
So what I think happened was during travels, the tube pins had stretched the sockets, therefore not connecting to the tubes properly, causing the capacitor to blow.
Any thoughts, please feel free to add
Cheers Brett
