1/7/2024 0 Comments Marshall mg100hdfx![]() ![]() I unplug everything, try another fuse, turn it on, blows it immediately and see some smoke come out of the fan unit. I put in another fuse, switched it on, blows it. Keep in mind I know nothing about electronics. I could smell smoke, took her apart, fuse is fried. I cranked it up to 5, played about 2 minutes of one song, and it blows and powers off. After checking my connections, I changed my instrument cable and unplugged the footswitch, for some reason it worked fine for about 5 minutes. During sound check, it was making an awful, indiscernable chirping, screeching sound. I had been playing it all week in practice with the master volume around 3. I had a gig last weekend and brought out my early nineties crate 4 x 12 extension cab to make her a full stack. I bought, used, a Marshall MG100HDFX head and matching cab about 2 weeks ago. Hope this helps someone else down the road.Hello everyone. And another note to the next guy, the traces on this board are kind of crap. There is still the really weird volume difference in Clean channel between clean and crunch, but I my swap in a lower resistor to see if that balances it out later. It actually sounds half decent even running a crap speaker. I swapped it out mostly expecting a meltdown immediately.īut no. Luckily I had a pair of spares in my box. Went back and traced the other way to IC7. ![]() I checked it anyways and -vdc was right where it was supposed to be, and not on the same trace as my rogue voltage. I traced it to IC1 first, but lost it at the last cap or resistor before the IC. I switched over to DC and started looking at the connections at the base of pots and sure enough, -vdc13.9 at the two right legs of the Vol pot (OD side) The same on contour pot, but on adjoining legs. Finally getting my ambition back and not having any of your addresses to mail this thing to, I plugged in again and hit it with my meter. of course wondering what I had shorted out messing around. as soon as it hit probably 3 on the clock I got dc to the speaker. Then (and I have no idea if I ever did this before) I turned the Volume down. I was getting some weirdness at the Volume and Contour pots. I decided to start looking for a signal on AC at the pot connections. Just when you are ready to give up, give it one more try. The should be at 0V wrt ground if they are there to pass signal only.Īlso check your supply rails on them pins 8&4. Use the schematic and test on pins 1&7 on all 8pin opamps. maybeĪnyways, I know this a much beloved amp, so if there are any more technical ideas for me, please chime in.Īnyways, I know this a much beloved amp, so if there are any more technical ideas for me, please chime in.Do you have a voltmeter? I would check the opamps in that section. I am now testing what i can of the Channel Select section ( maybe I should have scrolled down on the schematic first) Thinks are becoming clearer. Had complete sound loss for a bit when I fiddled around and knocked these out. ![]() Also replaced a couple zener diodes (one a switching d) on the front right corner near the master volume pot. I have thus far tested every resistor in the Overdrive section, per the schematic and all are good resistance. Overdrive is coming on, gets LED and Clipping LED's are working when playing, but no sound output from either speaker cab or headphone. Tested the pedal jack by using a chord and shorting it. Master control section working great as well. Started new thread for topic: per Enzo's suggestion.īringing it up to speed, Clean side works fine, with DFX and Reverb. ![]()
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