Fixing Digitech Death Metal

[supernaut]

Im trying to fix a Digitech Death Metal distortion that's having issues turning on. The switch basically does nothing. I can have battery or an adaptor connected and when I hit the switch no light comes on and I continue to get the bypassed sound.

I have checked the board and there's no physical evidence of any blown caps as I was suspecting whoever owned it before me used the wrong power adaptor or something. I have also checked the continuity on the switch and it definitely makes a connection when pushed. I've also checked the diode to prevent reverse polarity.

Only thing I can really notice is that there are two SMD resistors in parallel just after the diode. Before each resistor I get 9.4v and after is 2.3v. I understand that two resistors in parallel is a voltage divider but does 2.3v sound small? After some more digging I found that I'm getting that 2.3v all over the board beyond that point but the schematic is saying 4.5v. The two resistors I mentioned are both 220ohm (I measured on the board). It's really annoying that this part isn't mentioned on the schematic.

Oh also, it has the boss style momentary type switch on it.

Has anyone got an ideas on what to look at next?

Also sorry if this was in the wrong section, I had a good look and this seemed the most appropriate.

I'm including a couple of pics of the board itself. I couldn't find a schematic of the exact pedal but I did find one for a DOD FX86 Pedal which is essentially the same thing; I've included that as well.

[sominka]

Bin
buy new. Impossible to find the problem.

BW
Jan

[ElectricDruid]

Bin
buy new. Impossible to find the problem.

Not true! Just "more difficult" with things being little! Maybe not a "beginner project" though.

If the light's not coming on and you're not getting any effected signal, it sounds like the footswitch or the flip-flop aren't working to me. I'd start with that little tactile switch pushbutton that's been being stamped on its whole life...a mechanical failure is much more likely than an electrical one.

[supernaut]

Not true! Just "more difficult" with things being little! Maybe not a "beginner project" though.

If the light's not coming on and you're not getting any effected signal, it sounds like the footswitch or the flip-flop aren't working to me. I'd start with that little tactile switch pushbutton that's been being stamped on its whole life...a mechanical failure is much more likely than an electrical one.

Thanks for the help! I have tested continuity across the switch and it seems to work fine when pressed. I tested continuity to ground as well and it was fine. Is there anything else I should look for?

Also how would I test or replace the flip-flop?

[ElectricDruid]

Have you got a better photo of the component side of the board? I can't read what it says on the chips.

If we know what the chips are, we can have a decent guess at what the voltages should be. For the flip-flop, if we know which chip it is, we can find the outputs and see if they're switching.

The 220R resistors you mention is a bit odd - that's a very low value for a voltage divider virtual earth. If that is what it is, and the "midpoint" voltage is only 2.3V, that would explain a lot. Perhaps the cap across the lower resistor is shorted - that would drag the voltage right down.

[supernaut]

Yeah sorry about the photos. It was really hard to get a decent one (I only have my phone). I did take a slightly better one and I've written the code numbers on there for you. I'm not good at identifying these things so I just wrote out everything that's written. I also had another look at the resistors to double check I hadn't made a mistake and it's actually showing 290r for the top one and 270r for the bottom. I've also noted where the two resistors are in the photo.

I also had another look at what I assume is the reverse polarity protection diode as it connects straight to the power input/battery wires and I noticed that some of the covering might be exposed although it seems to read fine on the multimeter (I use diode/continuity setting and get the number 150). I've included a closeup of that as well. The code on it is SK14

[spoontex]

Hi,

finally could you find the fault?

I've the same pedal with the same problem!!