Vintage SD-1 noise

[Mike Z]

I have a stock 80's SD-1  that sounds like it has a ground problem
touch anything like the jacks or guitar strings and the noise goes away
other then that it sounds perfect
I checked the jacks ,the wiring different cables , power supply and even guitars & amps with no luck
Is there any good way to troubleshoot this ?
Would old electro caps cause something like this ?
Thanks

[GibsonGM]

Well, yeah, bad caps could cause something like that.  You seem to have a bad ground.  I would help to find the board ground, and work out from there, I think.   Also, make sure the switching jack is really doing its thing.

Try measuring for DC on the output of the pedal, with it on.  Just for grins, see if you get a reading...

[IsaacMoth]

If its an 80's SD-1, i agree that there is a pretty good chance the electrolytics are shot in there or close to it.

[Mike Z]

Thanks for your help
I checked the grounds at the board to the jacks and I guess the switching jack is working
Its turning the battery on and off
and no dc voltage on the output

[GibsonGM]

Ok.   If you have grounded jacks, and you know your cables are good, and you have determined that the BATTERY CLIP is ok....taking the effect out of the chain = no noise, as you said....you have played with the pots, wiggled them and turned them enough to tell if they aggravate anything?  (level pot has one end grounded)

Sounds like time to unhouse it so you can get at it.   I might try audio probing to see where the problem starts.....It REALLY sounds to me like something is ungrounded, and you may notice that as you take it out of the enclosure.  maybe something on top of the board you can't see should be grounded (I forget, I took mine apart 15 years ago, ha ha)   Be careful as you take it out, just go slow.

You cool with doing that - do you know how to solder, make an audio probe, are you handy and all that?  I am assuming the thing is going "bzzzzzz" until you touch the strings, like you described...we pretty much KNOW something is bad in a ground somewhere.

This is the schematic, not very complicated:
http://www.hobby-hour.com/electronics/s/sd1-super-overdrive.php

[Mike Z]

I have the skills but whats killing me is it works
I would think if something was disconnected it would not work
Not sure if the probe thing would work that traces the audio not the noise correct ?
Just lifting the board I can get a pretty good look inside & all looks good
I think checking the pots is a good idea maybe just cleaning them may do it
Thanks again for the help

[GibsonGM]

I have the skills but whats killing me is it works
I would think if something was disconnected it would not work
Not sure if the probe thing would work that traces the audio not the noise correct ?
Just lifting the board I can get a pretty good look inside & all looks good
I think checking the pots is a good idea maybe just cleaning them may do it
Thanks again for the help

Sure, Mike.  You almost wish something would STOP working, because this sort of trouble is the hardest to diagnose!   You MAY find an area where the signal is clean then goes to bzzzz with an audio probe...but maybe not - yes, often that is going to be systemic.    SOMETHING is wacked for sure.

Clean the pots, yes.   The LEVEL pot goes to ground - that is a way obvious place to check (with a meter) to be sure it actually has good contact with ground....moving part, you have a ground noise...hmmm....I'd be very suspicious of that pot.   Or the caps.

[Mike Z]

Well being one step away from a recap job
I pulled the Knobs and made sure the nuts were good and tight then I retested it
worked the pots ( no noise ) checked them with a meter they check good
so I cleaned the pots retested it and no noise
so I'm thinking no way and of all things it was the drive pot
so I rechecked all the grounds beat the crap out of the pots and I can't get it to fail
I sure don't understand it but it worked
I thought for sure it was a something looking for ground
anyway thanks for helping me figure this out

[GibsonGM]

You "cleaned all of the pots and no noise", man!  Good work - you had a problem, you worked it the best you could, and found a FIX.  I had fun helping you try to find the problem, too, you know.
 
Enjoy the pedal and please start doing DIY on here!  ) 

[Johan]

The chassis is grounded through the jacks via a star washer. If the unit is old, it might have become corroded.  Try loosen the Jack nuts, twist the jacks back and forth a little(be careful with the cables) then retighten the nuts. .. Just a thought. .
Johan

[GibsonGM]

The chassis is grounded through the jacks via a star washer. If the unit is old, it might have become corroded.  Try loosen the Jack nuts, twist the jacks back and forth a little(be careful with the cables) then retighten the nuts. .. Just a thought. .
Johan

+1