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Thread: repairing 1970s DIY on-board distortion unit

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    Question repairing 1970s DIY on-board distortion unit

    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!

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    Old Timer J M Fahey's Avatar
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    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.

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    Juan Manuel Fahey

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    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.

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

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    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.

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    Supporting Member eschertron's Avatar
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    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.

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    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


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    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.

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    Old Timer J M Fahey's Avatar
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    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.

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    Last edited by J M Fahey; 08-12-2019 at 06:31 PM.
    Juan Manuel Fahey

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    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.

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    Supporting Member eschertron's Avatar
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    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.

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    If it still won't get loud enough, it's probably broken. - Steve Conner
    If the thing works, stop fixing it. - Enzo
    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey


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    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.Click image for larger version. 

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    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

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    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.

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    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?

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    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

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    Last edited by dmeek; 08-13-2019 at 01:26 AM.

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    dmeek - That photo is strikingly familiar! Brilliant detective work!

    I've also found Google images of Univoxes that have the same labelling on the knobs. I've found a chap who discusses troubleshooting them: it's clearly beyond my abilities, but fascinating to find out that this puzzling and usually broken thing stuck in the back of my guitar is actually (a DIY version of) quite a famous effect. Thank you so much all.

    Anyone know a repairer in south or central London?

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    The board in your guitar doesn't look diy. It looks like it came from the original pedal and installed in the guitar

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    Wow. I'm definitely going to get it repaired then. I've found a place over here that sells them in kit form, I might ask if they can help. One of the qs for me was, will it sound as awful now I can play properly as it did when I was a kid? Given what it is, probably not! This has been such an interesting journey ... thank you all again.

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    Old Timer J M Fahey's Avatar
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    definitely the same: 6 transistors, 2 germanium diodes, same layout ... what else?

    But you forgot an important part: you treated us to two top pictures ... but none of the bottom, copper tracks side.

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    Juan Manuel Fahey

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    Try JPF Amps https://jpfamps.com/ at Regent Sounds in Denmark St. They’re members here, probably been too busy to visit for a while.
    Fixed fee of £22 plus parts for pedals, though not sure how current that is or whether it could be strictly classified as a pedal 😀

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    If it can't be fixed by someone on Denmark St., then I imagine nobody can fix it!

    My own personal view is that things that can be done better and more effectively off the guitar should be done off the guitar. In this case, a vintage FY-6 circuit board, rehoused to an enclosure with a suitable stompswitch, and tone-selector switch, could be worth a fair amount. Not retirement-sized, but certainly enough to more than cover the cost of the repair.

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    pdf64 - many thanks! I actually bought the guitar all those years ago in Macari's, which was in a different lot than it is now. They said it had a box in the back, but they couldn't charge me for it as it was broken. Dad fixed it for a short while by sticking back the black wire (5th one along) which was self-evidently not attached at the time. I'll contact Regent Sounds and see what they can do - that's a reasonable price.

    Mark Hammer - agreed about nobody else having a better chance of fixing it. My instinct is to leave it in the guitar, just for nostalgia, but I'll see what the repairer thinks - there is a chance that being housed this way is making it more prone to damage (eg, I have to wiggle it to get the battery in/out). I aint sellin' unless it really is retirement-worthy!

    JM Fahey - germanium? Even cooler! I do have a photo of the underneath, but my "upload" box is full. I was hoping to post a pic of the battery clip, in case that is shot, because I reckon even I could replace that.

    If I get it going, I may post an update. I love a good anecdote, and you've all been so helpful ...

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    Here are the wire connections for the pc board.

    Red- Battery Positive
    Orange- Expander control Wiper
    White- Expander control CW
    Blue- Input to foot switch
    Black- Circuit Ground (Earth)
    Brown- Output to foot switch
    Yellow- Balance control wiper
    Red- Tone switch
    Green- Tone switch

    Hope that this helps.

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    52 Bill, that's incredibly kind ... thank you for taking the trouble. Since nothing at all is coming out, I'm sort of wondering if my re-attaching of the battery clip was bad.

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    For anyone still following ... I now realise from 52 Bill's helpful list, that the wire I attached to the battery clip was the brown one that's supposed to go to the footswitch.

    I've had my share of help, but two last questions: this leaves my battery with just one wire - the red positive one. Is this OK? And, if the brown is, as it looks, too short to reach without being taut, is it OK to buy a new piece of wire and replace it? It doesn't have to be special wire, just the right gauge?

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    Supporting Member The Dude's Avatar
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    Just about any old piece of wire will work (within reason). That circuit won't draw much current. Generally, on an active guitar, which this basically is, the battery ground will go to a stereo input jack ring. The ground is then completed when a standard 1/4" jack is plugged in shorting ring to sleeve. This keeps the battery from draining when the guitar is unplugged.

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    Don't forget the joker g1's Avatar
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    Have you inspected the clip itself? Often stuff that sits for a while gets bad corrosion on the clip contacts.

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    The battery clip should have a red wire and a black wire. The black wire usually goes to the ring contact of the input jack. This way the battery is turned off when the input plug is pulled out of the jack.

    I would assume that the guitar has a stereo output jack installed. The black battery lead should go the ring contact of the guitar jack.

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    Old Timer J M Fahey's Avatar
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    plus:

    52 Bill

    Here are the wire connections for the pc board.

    Red- Battery Positive
    Orange- Expander control Wiper
    White- Expander control CW
    Blue- Input to foot switch
    Black- Circuit Ground (Earth)
    Brown- Output to foot switch
    Yellow- Balance control wiper
    Red- Tone switch
    Green- Tone switch


    In principle, and just for testing, connect battery clip Red to Red on PCB, and battery clip Black to Black/Ground/Earth on PCB.

    This will put Fuzz ON , not depending on external switching jacks or wiring and it will either work or not, period.

    IF it works, pull battery after testing and we´ll wire the switching jack

    IF not, eitherv repair PCB or build a new one and replace it.

    But there´s high probability it works, simply not getting power yet.

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    Juan Manuel Fahey

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    Great ... I'm going near a hardware shop later, so I will look for suitable wire there. I think the clip contacts are OK, I guess I could buy a new one in case, I doubt they cost much. I'll do the test using the PCB earth, and if it works, then I'll go ahead and put things together properly as suggested. If the test doesn't work, it's off to Denmark St for a professional repair.

    I'm very grateful.

    Paul

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    Old Timer J M Fahey's Avatar
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    Good.

    Buy a small roll (10 meters?) of stranded (not solid) 0.35mm^2 wire.
    If the only one you´ll ever buy I suggest white or grey colour which are "neutral" ; while Red, Black, Blue or Green are typically associated to Positive, Negative, etc. and that might be misleading in the future.

    In the old days I used to buy Electronic stuff in the shops along Edgware Road or Tottenham Court Road but all disappeared or at best sell cellphones and tablets.

    Oh well.

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    Juan Manuel Fahey

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    Thanks, Juan Manuel - very helpful to know the size, I was wondering about that! I got it off the internet in the end - should arrive Saturday. Yes, I go to Tottenham Court Road often, and those shops are just cellphones all over, plus a few overpriced digital camera places. I bought a roll of film in one recently ... oh man! The price ...

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    The traditional means of applying power to onboard effects/circuits is to use a stereo jack. Insertion of the guitar cable into the jack will turn the battery power on, just as it would for stompboxes.

    Having said that, I suspect a great many here have committed the same error I've committed at least a few times in their life, and that is to connect the black wire from the battery snap to the wrong solder lug on the jack. 1/4" stereo phone jacks are not quite as standardized in the location of the different solder lugs as we'd probably like them to be, so it is also possible the battery snap is soldered to the wrong lug on the jack.

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    Senior Member vintagekiki's Avatar
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    Quote Originally Posted by TheresanLinSolder View Post
    OK ...

    Click image for larger version. 

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    The PCB is definitely factory.
    Is there any information on the printed side.
    Which guitar is it (model)

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    vintagekiki - on the reverse the PCB has a large metal area in the middle, with SF-1. That number may continue - there's a wooden post into which the board is screwed, which obscures any other letters (the post, I think, used to be glued to the guitar body, to keep the thing in place - it's now unstuck). The guitar is an old LP copy, branded Saxon, which I believe was marketed by Selmer, and sold under other badges in other countries. I have a fantasy that the guy who did this work is going to appear on here, saying, that was my first project and I'm now a famous engineer ...

    Mark Hammer, and others, thank you - I've googled for images of mono vs stereo jacks - the "in" on my guitar is indeed stereo, the two "outs" are mono. There's a black, presumably earth, which appears to go from the stereo-in across to the extra mono out, then from there to the back of the Expander knob, then to an area I can't make out. The earth from the board (per 52 Bill's list above) goes first to the 1-tone-2 switch, then to the area I can't see. That area is the rear of the Balance knob and the on/off switch.

    Is it reasonable to assume that in the obscured area the 1-tone-2 earth connects to the balance then the on/off, and then out to the expander and so on? In other words that we have one long chain of earths from the board, to each adjustable control, then to each of the extra sockets? If so, may I connect the battery ground to the black connection on the board? Or should I still go to the stereo socket? Or just any easy place along that chain? (The guitar's original socket is out of this loop, it has thicker wires, in red and grey.)

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