Red Llama debug

James · Post by **James** » Mon Sep 15, 2008 6:34 pm

UPDATE

The pedal works but only in one position on the volume pot. It's just below maximum. Above or below this and there is no signal at all, and it's quite splattery as it enters and exits that area. I changed the pot to another (5k log) and it reacted the same with a slightly different "it works here" point.

So I'm guessing there's a problem with one of the components near the volume pot in the circuit. I'm going to try checking for voltages and seeing if anything is obviously up.

The pedal sounds good in the spot that it works in, a slightly fuzzy overdrive. The fuzz part works as it should too.

Post by **Mike** » Mon Sep 15, 2008 8:28 pm

You're doing everything I would. Have you tried waggling your wires from the volume pot about? I would reflow all joints around them.

aen · Post by **aen** » Mon Sep 15, 2008 8:39 pm

I had this the other night with a Destroyer. I had a crack in the copper coming off the chip, so basically, a shitty joint wayyy back in the chain.

James · Post by **James** » Mon Sep 15, 2008 8:41 pm

Yeah I've done that and resoldered (well resoldered one and just rehated two) on the board. Replacing the pot showed no difference. I'm fairly sure it's just something like a bad solder joint on a resistor or capacitor going to the volume pot and it's causing it to spazz out slightly. The actual sound of the fuzz circuit seems right (I'm not that familiar with the way the circuit sounds but it sounds good enough and enough like demos I've heard to believe it) so if I just tame the volume pot it should all be good.

I have to get destroyed at Mario Kart Double Dash before my cousin goes to bed (he's staying over while his mum is in hospital, so I'm giving him a game) and then I'll have a go at fixing it.

If I do get it fixed, expect a fuzz factory debug thread to follow. It's close to, and I'm not sure what's up with that either.

Post by **Mike** » Mon Sep 15, 2008 8:43 pm

This is all good for the soul James. Shit like this happens unfortunately.

Some close up pics of the FF would really help I think.

James · Post by **James** » Mon Sep 15, 2008 9:33 pm

I've possibly narrowed it down to a cap. In the old diagram (the second one I posted) it's a tant cap, I use electrolyte. I salvaged the tant cap from my previous failed build and I'm going to try and find out what the markings on it mean with regard to polarity, and then install it in the place of the one I have there now. I could just reverse the electrolyte, but I figure I may as well make use of the cap now i've salvaged it.

Comparing the cap that's in there now to the diagram with polarity marked it is the wrong way, so it's defintely suspect #1 at the moment.

James · Post by **James** » Mon Sep 15, 2008 10:06 pm

Switched caps and it made some funky noises. Low oscillating type tones like an ultra fuzz can do but lower and dirtier. The volume pot was seemingly worse than before but had the same problem. Something is still amiss.

Here's my debug diagram of where components are compared to where voltage is. Highlighted in blue = voltage, red = no voltage.

I fixed the red area around c6 by installing the tantalum cap, but the others remain. The ground rail is supposed to be zero though right?

Post by **Mike** » Tue Sep 16, 2008 7:33 am

yeah Ground should always be zero volts in a standard build (we'll get onto positive ground some other time), since your black multimeter probe will also be on ground.

Pull the tant and put the electrolytic in the other way round.