Help needed for my Lal fuzz 88

[Christophe]

So my beloved oscillo fuzz 88 started acting funny a few months ago. Maybe some skilled Ilfers might help me point out what's going on? ( I took it to my repair guy but the pedal is so unusual and no schematics that he just didn't know what to look for).
Here are the symptoms:
-I'm not getting high end oscillation on most of the switch positions. I'm still getting the sub-oscillations.
-Initially, there was only 1 or 2 switch combinations that would make no sound at all. Now there's like 4 or 5.
-on the whole the pedal is less gainy, eventhough some settings feel exactly the same as ever

Thanks to Jero I now have a schematic. It could be just one component that needs to be changed but I have no clue about that.

If you guys have any idea, that would be much appreciated!
Thanks a ton, keeping an eye on the next available 87 in the meantime ;-)

[crochambeau]

Without studying a schematic I can only contribute a few vague guesses.

Electrolytic caps, if present, in oscillator circuits can show their age.
Supersonic oscillation pulling on a power rail can affect apparent gain in unrelated sections (and fuck over other oscillators).

I suggest measuring DC potentials at transistors/actives and probing around with an oscilloscope hunting for unhelpful signals as a starting point.

[Christophe]

Without studying a schematic I can only contribute a few vague guesses.

Electrolytic caps, if present, in oscillator circuits can show their age.
Supersonic oscillation pulling on a power rail can affect apparent gain in unrelated sections (and fuck over other oscillators).

I suggest measuring DC potentials at transistors/actives and probing around with an oscilloscope hunting for unhelpful signals as a starting point.

Hey thanks man! Here's Jero's link to the schematic, if that's helpful:
https://drive.google.com/file/d/1Sj8dGH ... EeAEo/view

I'll gather everyone's ideas about this and send a report to my repair guy, for him to get a better idea of the problem, and see if he can deal with it or not (totally not my field!)

[crochambeau]

That's something of a tangled path.

I would also scrutinize the switches. You say there are switch combinations that do not pass sound - are there any single switches that do not change function or consistently kill sound?

I have not digested what the normalled connections in the EXP jack support, but if there's oxidization or muck on those leaf switch contacts that can affect things as well.

[Christophe]

That's something of a tangled path.

I would also scrutinize the switches. You say there are switch combinations that do not pass sound - are there any single switches that do not change function or consistently kill sound?

You can only wild-guess what the switches do, since the pedal doesn't have a base tone, you can only hear a version of what the pedal can be depending on the switches combination. there must be things like osc, gain boost, oct up, etc... but how you combine them sometimes has a cancelling effect: there is one or two specific combinations that consitently kill sound (on every fuzz 88). It is not a blank like when a pedal is not working at all, you can still hear a bit of noise floor. But now I find more combinations that kill sound.

I have not digested what the normalled connections in the EXP jack support, but if there's oxidization or muck on those leaf switch contacts that can affect things as well.

My friend opened it to check that out, but there's no red flag (visually) when you look inside the pedal. So it doesn't look like a switch problem, but then again I'm no expert.

[digi2t]

The circuit itself is pretty much bulletproof. If things are happening when you throw switches, I would do a simple continuity test on each switch to ensure that they are all OK. It's an A/B deal, so if they check out, I would check the following;

- Power section filter cap leakage to ground (C2 - 10uF cap on the DEFX schemo). This could be causing a power sag, which would explain the loss of the high oscillations, but the low still being present (think Sag control on a fuzz). Considering that +VE feeds three of the six switches, I would start there. Maybe check the power diode (D3) as well while you're in there.
- Audio probe it to see if there is a drop out part way through. A bad resistor along the rails could be a possibility. Doubtful, but...
- Bad solder joint. Just reflow all of them to be sure. Doesn't cost anything, and easy since the solder side is up on these anyway.
- If your repair guy can't find his/her way through such a simple circuit without a schemo, consider replacing them first.

If you're in North America, and can cover the shipping to Canada and back, drop me a line. I can look at it for you.

[Christophe]

The circuit itself is pretty much bulletproof. If things are happening when you throw switches, I would do a simple continuity test on each switch to ensure that they are all OK. It's an A/B deal, so if they check out, I would check the following;

- Power section filter cap leakage to ground (C2 - 10uF cap on the DEFX schemo). This could be causing a power sag, which would explain the loss of the high oscillations, but the low still being present (think Sag control on a fuzz). Considering that +VE feeds three of the six switches, I would start there. Maybe check the power diode (D3) as well while you're in there.
- Audio probe it to see if there is a drop out part way through. A bad resistor along the rails could be a possibility. Doubtful, but...
- Bad solder joint. Just reflow all of them to be sure. Doesn't cost anything, and easy since the solder side is up on these anyway.
- If your repair guy can't find his/her way through such a simple circuit without a schemo, consider replacing them first.

If you're in North America, and can cover the shipping to Canada and back, drop me a line. I can look at it for you.

Hey thanks for the comprehensive input, and for offering your help! I’m in France so that’s a long way, and had my share of carriers and problems ! But why not... I’m gonna forward this info to my friend and see!