repairing 1970s DIY on-board distortion unit

[TheresanLinSolder]

Hi everyone. My first guitar, which I've owned since the 70s, has a homemade distortion unit in the back (courtesy the previous owner). It hasn’t worked for years. Having recently got a soldering iron to change some pickups in a different guitar (a huge job for me!), I decided to have a look at the circuit board in the old one.

A wire had snapped off the battery connector. I re-soldered it, but there’s still no sound. I’ve wiggled the knobs repeatedly, but it’s dead. The setup is that you take the normal out cable and plug it back into a second jack socket, through the board, and then out a third socket to the amp. In this config, the guitar plays fine in bypass, but when I depress the on switch (by Shin-ei!) it goes silent.

All the wires connect to something, there are no smoke or burn marks, nothing is melted.

Is there a way to find which component has broken? I've Googled and found multi-meters, but they seem (I think) to show if the circuit is continuous. I know it's not! I want to find out which bit has gone wrong.

For interest, most of the components are small multi-coloured cylinders, a couple of them translucent; some squat grey cylinders; four sucked-sweet shapes in brown, two large, two small; and some hard to describe black plastic things that are almost like a cylinder with one flat side.

Thank you!

[J M Fahey]

Sorry but you´ll have to find some Tech who can read schematics, identify components, measure them, measure voltages, use a multimeter, etc.
Otherwise it´s an impossible task.

[Mick Bailey]

I have to say that method of connecting an onboard FX unit is a first for me. So, there's a completely standalone fuzz sitting in there that you plug into like it was a cased pedal. Troubleshooting this would likely be straightforward, but you need a certain level of knowledge and experience to begin with. It could be just that the circuit isn't receiving power - this is the first check, but you could inadvertently cause more damage to the circuit by accident and make things more difficult for the next person who works on it. I would seek out someone who can either carry out the work or who can help you with it. We can provide assistance here, but I think we're just too far apart in terminology - even down to the basics of identifying components.

[Mark Hammer]

A pic of the control cavity and circuit would help a lot in sussing this one out.

[TheresanLinSolder]

Thank you all - my camera battery is recharging, I'll try to get a pic in due course. Yes, I am aware this is not my specialism! If it's a joint that needs resoldering, I can do that. If it's a component, well, I'll only try if it's clear what it is and how it connects. And yes, I've never met anyone else whose guitar has three jack sockets! It's an LP copy, they're all on the lower rim. Doing it that way allows you to stick a second (better) guitar in and use this one as a fuzz box only.

[eschertron]

Are you sure that the input to the fuzz box and the output from the fuzz box are correctly identified? Plugging the guitar signal into the output will most definitely result in no signal. And if the effect is "true bypass" then the bypass would still work. Just a thought.

[TheresanLinSolder]

Thank you eschertron - good point. Yes, I have a memory of how this one goes, which I stuck to. Then I tried it the other way in case. Same result both times. Usually, if I connect a pedal the wrong way by accident, the bypass option works but still sounds a bit odd - that's the case here when connected back to front. In neither case does the effect work. I've also changed the battery, just in case.

[J M Fahey]

In any case, I am pretty certain it must be some kind of Fuzz.
Personally I´d just buy/build a fuzz inside some case, including a 9V battery (they last forever since consumption is very low) a footswitch to avoid the time wasting plugging in-out and use it instead.

Or have some Nerdy Techie type friend build one for you, and include its board inside your guitar.

Not hard to build, they are one of the favorite ways to start building something Electronic, if interested we can suggest you a couple sites covering all, from PCB (or even perfboard building) to assembly to testing to sound samples.

[TheresanLinSolder]

Ah ... JM Fahey, thank you - I have a variety of effect pedals, including fuzz, that work. This is a guitar that I bought in 1979/80, when I was 14. The effect used to work, but now it's broken. I'm just trying to fix it for nostalgia, and also to see what it sounds like after all these years, now that I can play properly. It's a pretty basic effect, that I would describe as distortion, really (IIRC). It's a cheap guitar, but I'm very fond of it, and would love to hear the effect again.

[eschertron]

Can you physically remove the effect from the guitar, so as to take pictures from all angles? There are some wizards here that can mentally de- and re- construct the circuit just from looking at it. You'd get opinions on what kind of distortion unit it most closely resembles, and how to test it for failed components and proper operation.

[TheresanLinSolder]

OK ... thanks for the suggestions/cautions so far. I've had trouble uploading pics (they keep crashing, and are too big), but I think I may have solved this at last. We have the board, the battery clip, board from beneath, and for interest the top showing the knobs and labels, and the extra jacks. I'll have to post these as separate messages, owing to size limits.

[TheresanLinSolder]

Oh dear. I can't see a way to delete those two files from my upload manager. That means I can't upload any others for 1 hour. Did I say I'm not much good with computers either?!?https://music-electronics-forum.com/...s/icon_sad.gif

[52 Bill]

From the photos of the pc board, that looks like either a Univox Super Fuzz or a similar circuit.

You can probably find a schematic online somewhere and then see if the circuit has been connected correctly.

Good luck.

[TheresanLinSolder]

52 Bill - cool! Thank you. It looks as though I can't upload any more photos, those two took me very close to the limit, and they won't delete. But ... the controls on top (which I'd hoped to show) are a knob for Balance, another for Expander and a sliding tone switch, to go between tone 1 and tone 2 (from memory 2 was scooped). Is there a component that often goes wrong in that circuit - you know, a well known weak spot?

[dmeek]

Good call

It's a Shaftsbury Duo Fuzz or Shin-ei FY-6 or Univox

Look at the third pic in the first row

http://www.gear-review.co.uk/reviews/duofuzz/index.html

and here

https://music-electronics-forum.com/...ad.php?t=10110