Dead 1979 IC Big Muff V5

[chuckfalcon]

Hi everyone.  I have a dead big muff over here and I could use some assistance.  So far I have checked connection and reflowed solder and I am not getting anything when the effect is engaged.  I am getting bypass but no fuzz.  Does anyone have any suggestion?  Any voltages I can test or anything?n  Ive never tackled an ic effect before.

Any help at all would be appreciated.

Thanks,
Chuck

[pinkjimiphoton]

make sure your pots haven't gone open, i find that a lot in older EH pedals.

but we can't tell much without voltages. stick your black meter lead to ground, and write down the voltages of each pin on the IC
and we should be able to help you.

i would replace every single electrolytic cap on the board as well. i do that as a matter of course always with every old effect i get.

[reddesert]

Getting up on a soapbox:
I don't think it's a good idea to replace electrolytic caps wholesale in a pedal until after the fault is located. Browsing pedal and guitar sites, I often see reports where someone started by replacing the capacitors, it still doesn't work, and eventually it turns out to be a loose ground, bad switch, etc.

Pre-emptive replacing of electrolytic capacitors is a good idea for a vintage tube amp where the caps are old, highly stressed due to high voltage, and if they fail, they can take out other more expensive components. For a pedal, cap failure is less likely and much less critical.

What harm can it do?  In PJP's experienced hands, very little. But for a less experienced person, every time a component is desoldered, there's a chance of damaging the PCB, and it delays diagnosis of the problem.

[reddesert]

Just so my contribution isn't completely useless:

When diagnosing circuits, I find both voltages and using the audio probe to follow a signal through the circuit to be very helpful.  For a typical op-amp circuit, you should have 0 volts on the negative supply pin, the positive voltage supply (usually 8-9 volts, unless a charge pump is in use) on the positive supply pin, and roughly the bias voltage (usually 4-4.5 volts) on the input and output pins.  These change if you have a bipolar voltage supply, which is rare in pedals (but typical in amps).

IME mechanical failures (loose wire, bad switch, bad pot) are more common than blown electronic components.

[pinkjimiphoton]

well, 1979 was how many years ago?


them caps fail in them old eh boxes, i fix 'em all the time. first things first, yes, check out voltages etc, but 38 year old caps?

i still say change 'em. often it's all it takes to bring stuff back. but i must agree, its easy to mess stuff up worse.
if ya look on RG's geofex site about restoring vintage effects, its one of the things he reccomends as well.

if ya have bad electros, you can @#$% with it for weeks and it still won't work. the more stuff ya can mitigate that fails often the better your chances of success often will be, if the caps are bad, the pedal will be dead. especially this particular circuit which is kinda weird to begin with.

first thing they taught me back in amp repair school (hhahhhah....like i went to amp repair school) is to start with the power supply.

if i have an old amp, same thing. yes, i can re-form the caps (sometimes) with a variac over the course of a day or so (sometimes)
but its usually quicker and easier to cut to the chase and replace the parts most likely to have failed.

you may not find out which exact part failed by doing this... but at 40 years old, they are all due to fail and imho you are as likely to damage the box more opening it again at a future date than just doing whatcha gotta do in the first place.

first thing that always fails in most circuits i've encountered is the electros. if they are bad, they kinda kill everything else. either they go open or they short, but either way they tend to be the first thing to go.

just my opinion... the guys are right with their counterpoints, i'm just going on my personal experience. i don't trust old electros in anything. amps, effects, keyboards, whatever...i tend to replace 'em all first thing so i know my power supply is good.

doesn't make me right at all just the way i do it.