Hi, I don't know if this is the correct place to post this. Please inform me if I'm in the wrong section. Anyway I'm modding and fixing an mxr distortion+ rev d. Saw one burnt resistor just below the dc power jack. It is tagged as R9 in the pcb. Anybody know the value? I tried to test it with DMM but got no value and google provided schematics, but only up until R6. It kinda looks like a 1M value so I replaced, but now pedal won't turn on. Here are some pictures.
Looks like Brown-Black-Black-Gold-Brown, or 10 ohm (1% tolerance). I'm guessing its used as filtering on the power rail.
Plugging a 1M in that spot (assuming I'm reading the board right) would limit the circuit to .01 milamps, not enough to power it.
You could probably put a 100ohm in there to get a similar filtering effect with a little more wiggle room before popping.
Currently digging up board pics to confirm that, but that's my current hypothesis.
Thanks for the reply somnif. I'll replace the 1M with 100 ohms when I get home. I suspect those two resistors have something to do with the 9v power since they are solder there with the jack. Don't know why that resistor got burnt because the owner said he seldom uses the pedal and just keeps it in the shelf.
Will keep you posted after I replace r9. Thanks again.
Quote from: vicfiveleven on July 22, 2019, 06:19:06 AM
Thanks for the reply somnif. I'll replace the 1M with 100 ohms when I get home. I suspect those two resistors have something to do with the 9v power since they are solder there with the jack. Don't know why that resistor got burnt because the owner said he seldom uses the pedal and just keeps it in the shelf.
Will keep you posted after I replace r9. Thanks again.
Reading around it appears to be a not uncommon fault (finding several forum posts about the same issue). I know Madbean used to use a 10ohm filter resistor on some projects, and they would have a similar burnout fault on occasion, so upped it to 100ohm (or left it out entirely).
The smaller the resistance the more heat the thing is going to (try to) pump out. The circuit is dead simple, probably only draws ~5mA on its own, plus maybe 10-ish for the LED, but any number of things could briefly spike the power draw leading to that poor little component going poof.
100ohm will give you more wiggle room in that regard, while still retaining the power filtering duties the old R held.
For some reason I just happen to have a green board Dist+ board kicking around and R9 is a 10R.
Soldered 100R on r9 and it worked. Thanks a lot!