rustbucket resistor smoking!

[tomasjjj]

hi guys, been lurking here for a month or so now, but been busy with work to get on with some building. so, hi!

randomly found a pcb for the rust bucket on ebay a few weeks ago (along with some other boards) and ordered up the parts to solder them on.

however, once i plugged it in, my 1/4watt resistor at R46 started smoking and burning up!

ive checked over for cold solders, wrong values etc, and all seems ok, power supply was 18v, and even tried a 9v battery and the resistor continued to smoke out.

any idea what could be happening?! tried a max1044 as well as the lt1054 for ic13 with the same result... smoking r46!

[thesmokingman]

you need to trace and continuity test your power supply components against ground as a start. expand from there and test the rest of the circuit.

[EBK]

Check to see if you happen to have continuity between the right-hand side of that resistor and ground. 

[tomasjjj]

reflowed the joins around that area, but dont have continuity between r46 and ground. i do how ever between r46 and ic13 and pin 8, and between r46 and c13, which is 100uf and connected to ground.

whats the purpose of r46 as 22r seems a bit of a strange value?

annoyingly i cant plug it in long enough to get voltage readings as im scared ill burn the traces up off the board!

[midwayfair]

whats the purpose of r46 as 22r seems a bit of a strange value?

It's part of a filter formed with C13 to clean up the -15V power to some of the components.

There shouldn't really be enough current draw there, but that doesn't mean that 1/4W is sufficient. Try replacing it with two 47R in parallel to simulate a 22R 1/2W, or try simply jumpering it if you think your power supply is fairly clean and seeing if the pedal works properly without it. If the pedal works, then pick up a 1W resistor next time you get something from Mouser. They have some made by Dale up to 2W that are about the size of 1/4W.

[tomasjjj]

ideal, cheers for the info, will give it ago! cheers

[tomasjjj]

So tried the half watt resistor idea, but same smoking. So to try and get some voltage readings I pulled all the ic from their sockets. Voltages looked OK, but as I put the ic back on one by one as soon as I got to ic 7 and 8 the smoke started again, guess I've found the area to continue looking!