Pedal repair

[IK7]

Hi there,

I'm hoping someone on this forum will be able to help me try and repair a recently acquired DOD FX56.

The problem is that there doesn't seem to be any power getting to the circuit. I've checked all the wires and swapped out the switch for a known working one, but for some reason it just seems...dead. If I disconnect the black lead (-) from the board itself, the LED will come on, but there is still no sound. I've even tried unsoldering all the wires and connecting the board to another shell to rule all the jacks and power connections, but still nothing.

Where would be the best place to start with trying to figure out why this thing is dead?

[vigilante397]

Hi  Welcome to the forum. The best place to start is here:

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Some of the information here isn't relevant, but getting voltage readings and posting pictures is a very good place to start.

[IK7]

I'll have a proper look tomorrow using that guide and get voltages for each section, hopefully its something simple.

[aron]

First question: Do you have a multimeter?

[IK7]

Indeed I have my trusty digital multimeter.

I will post pictures of it later as well as the schematic.

With the pedal all connected up normally, with power and a lead in the input, the pedal won't power on, but i've tested the switch so, i'm a little stumped straight away =/

[IK7]

Right, managed to get a couple of pics:











So from left to right, the connections go:
Black - Ground
Yellow - Positive
Green - Switch
Brown - LED (+)
Blue - Output
Green - Input

The only thing I really noticed was a tiny hole in the bottom of the first filter cap, but this looks like its meant to be there.

Any starting suggestions would be great, even if I can wire it so its permanently on would be a good start.

[Mustachio]

Maybe the 1n4001 diode is hiding under that big 330uf cap. Polarity protection diode , maybe it was plugged in with the wrong power supply and it popped that diode.

You can see it in the top left of the schematic that would be the first thing id check. Good luck!

[IK7]

Ok, i've made some progress...I think.

I checked the diode with my meter, which was showing flow each way, so I took the diode out of the circuit, which tested as working, however I replaced this anyway.

The next thing I did was probe with a battery connected, which gave me voltage up to the diode and then at the 100Ohm resistor. While I was probing and flipping the board about I touched the 100Ohm resistor and it was extremely hot. I don't get any voltage at the other side of this resistor, but could this be because I can't turn the circuit on?

Also, why would the LED come on when I lift the black wire from the board?

[Mustachio]

Yeah I don't think that resistor should be getting extremely hot and you should be getting voltage on both sides of it. I'd change that resistor and clean up the area around the black and yellow wire's pads on the board it looks funky there could be having a solder bridge.

[IK7]

I have changed out the resistor and cleaned up all the pads, but its still the same. The new resistor gets hot still and I don't get any voltage on the other side of it.

Is there something blindingly obvious i'm missing here? I can't get any voltage readings from the ICs as i'm getting no voltage on the other side of the resistor.

[greaser_au]

The series resistor dropping all the voltage, and getting warm, suggests there is a short to ground on the power rail. is anything else getting warm?

Have a good look for solder bridges and components bent against one another.  The 100u (330u?) filter cap is a candidate,  as are all of the ICs (as they connect directly across the supply rail & ground).

david