Pedal Parts - Muff Gun build - fault diagnosis...

ewal

Argggh - I'm not having much luck with my recent pedal kit builds. Just built a Pedal Parts Muff Gun which is a Blackout Effectors Musket copy...

With the circuit engaged there is a massive drop off in volume, however the volume comes back as you turn the Tone down... This is not such an easy pedal to do my usual limited fault checking of re-flowing joints, as the pots are soldered directly to the board and therefore get in the way of the solder points.

I don't suppose there's anything obvious to look for based on the fact the volume is so obviously interacting with the Tone control?

Thanks

lasermonkey

If you put the Mids control at 12 o' clock, does the problem persist?
 While I haven't built one of these, I believe the Mids  control is the AMZ mids mod for the Muff circuit, and I'm aware that it can drop the volume drastically when fully clockwise. Turning the tone control anti-clockwise takes that out of circuit, so it's a good place to start looking.

lasermonkey

Also, I assume none of the potentiometer bodies are shorting against the PCB? Looking at the instructions, it mentions that you can't fit the plastic-covered Alpha pots on there without removing the plastic covers first.
 If neither of those things, some good, clear photos would help. :-)

ewal

Thanks @lasermonkey The volume drop is extremely drastic to the point the effect is unusable unless the Tone is fully anti-clockwise. So in terms of start fault diagnostics with Tone control, is it a matter of looking for dry joints or bridges in this part of circuit? A fault diagnostics vid on Youtube suggested that this, plus having components in wrong place is a lot more common than actual component failure.

ewal

I'll post pics up later. I don't think any pots are shorting against PCB - I've covered the backs with insulating tape and put a bit of card between them and the PCB, because they do sit close to the board.

PS: I didn't post picks of my Harmonic Percolator build when asking for help as I'd made an embarrassing hack that I didn't want to share Decided to write this kit off to experience and get another board from Fuzzdog.

lasermonkey

The Muff tone control basically pans between two filters. If turning anti-clockwise removes the fault, the fault must lie in the other filter. You need to look at R18 (I think it's R18, the image is poor on my iPad), C10, C16, the Mids pot and pin 3 on the Tone pot, and the tracks and pads those are connected to. A hair-line short, usually only visible with a magnifying glass, could easily lead to the symptoms you describe.
 I'd definitely check whether the problem occurs during the final bit of travel on the Mids pot though, as I have seen that happen before. I think it's what they call a "feature".

ewal

Great advice @lasermonkey I will get the magnifying glass out this evening

ewal

Last thought at the moment - while board mounted pots make everything so much tidier, especially in a pedal with six pots - it makes fault diagnosis a massive pain in the bum...

ewal

A couple of shots, although I recognise that the shot of the pots is a bit useless, however can't get access to the other side of the board....

lasermonkey

It's difficult to be sure, as I'm seeing the pics in two dimensions only, but a cursory glance throws up a  possible short. On the top picture, it looks like there could be a bit of solder bridging between the lowermost pin on the top transistor and the pot leg below it. Might be worth looking at that for starters.

lasermonkey

Any progress yet?    :-)

ewal

Not yet @lasermonkey I've not had much time over last couple of days. Although I did find a filament of copper wire kicking about near one of the pins on the tone pot, and I've removed the suspect short you pointed out - although I don't think it was quite bridging.

I will report back later:-)

jonnygreentrees

I'm not sure if they would cause the symptoms you describe but are you sure you haven't fried any of the transistors? I normally socket mine as they are very sensitive to heat

BloodEagle

1st thing i'd check for is any solder bridges between contacts

ewal

I can't be sure I haven't fried any transistor, however I've never done this before and I was pretty quick soldering them.

I'm definitely going to carefully look for solder bridges this evening, although the board mounted pots are a bit of a pain in the arse - the question is whether I'll be able to bend the pins so I can get sight of the joints underneath, or whether I'll have to de-solder them, which would be really fiddly...

ewal

Might be on to something - found a suspect bridge between R18 and D3, however haven't had a chance to test yet as I need to do a bit of switch re-wiring. Fingers crossed!

ewal

Argghhh - I'm taking a break from this build... I might've have fixed the original problem, but can't be sure because now when I attempt to test, I'm getting no output at all.... I'm convinced there must be a short somewhere but have so far not found it... I'm getting bored building and want to get back to playing, so I'm going to set this one aside for a bit, and maybe come back to it fresh in a week or two...

ewal

A quick update... I ended up sending this off to Owen Electronics cause I was getting nowhere... Glad I did because I had really cocked this one up. His diagnosis:

Wiring to foot switch pcb to main pcb faulty with broken tracks on both boards. 

Wiring to jacks and dc input socket very poor requires replacing.

Pots shorting to board that tape is not good enough requires thick felt pads plus pots repositioning slightly.

Broken ground point on main pcb requires repairing.

Cross threaded jack nut will not tighten up requires replacing.

C19 hack poor solution better to fit capacitor with longer leads and sleeve.

There is a design fault on the pedal the input pull down resistor is 22K which is too low should be 2M2.

All sorted now.... I highly recommend his services, and I think my days of pedal building might be over given the mess I made of this one!!

lasermonkey

OK, you made a few mistakes on this one but, to be fair, it is a relatively complicated build for a novice. There is a lot of stuff crammed into a tight space!
Might I suggest that you try something a bit easier next time? Something with a much lower component count and maybe not so crowded. Take your time, get everything nice and neat (that's actually quite important, as it prevents any bits from touching when they shouldn't) and check each stage for shorts and mistakes before you proceed to the next. Soldering isn't something that people are immediately good at. It takes practice, much like anything else that's worth doing! And remember, there's always people on here that will help or offer advice if they can.
I am surprised at the pulldown resistor error, though. I can only imagine that it's an mistake on the schematic which wasn't picked up. It's probably a good idea to let Mr Fuzzdog know.

ewal

The annoying thing is I'd previously managed quite a few kit builds. Think I've obviously been getting away with some sloppy wiring in the past.... Although I like the Fuzz Dog kits I think the PCB's are a bit more fragile than the BYOC or Tonepad ones I've used before.