Anybody want to help with a pedal refurb project?

pikingrin

pikingrin

what is this?
I've got an (assuming) early-mid 80s DOD FX25 envelope filter that I bought off of ebay about 10 years ago. It worked then but it's starting to crap out a little bit. When the pedal is engaged the signal cuts out completely; disengaged it passes through as it normally would. If you hammer on the guitar strings it will cut in with the autowah sound but it's not worth breaking strings to get the pedal to function. Anyone know of a good starting place to check components for failures?

I have zero (0) experience working on pedals but I've got a few more that need some minor maintenance and I figured this would be a good starting point as it's normally not in my signal chain - it's one of those obscure pedals that I would be ok with using as a paperweight if I completely screw it up in the process... If anyone's got any advice I'd surely appreciate it!
 
There are plenty people here who will help, but the best resource I know of is What To Do When It Doesn't Work over on diystompboxes. You're going to need a decent multimeter, and an "audio probe". Probably a soldering iron and stuff...

TBH, unless you're really into learning and up for a bunch of frustration, I wouldn't bother with that particular pedal. Wasn't that great to begin with, and super cheap to replace. There's like four of them at my local music store any given day of the week.
 
ashcat_lt said:
There are plenty people here who will help, but the best resource I know of is What To Do When It Doesn't Work over on diystompboxes. You're going to need a decent multimeter, and an "audio probe". Probably a soldering iron and stuff...

TBH, unless you're really into learning and up for a bunch of frustration, I wouldn't bother with that particular pedal. Wasn't that great to begin with, and super cheap to replace. There's like four of them at my local music store any given day of the week.
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I've got a good meter but not a probe, not even sure what that is to be honest. Soldering iron and all that I've got and have more than enough experience with so that won't be an issue. I know, it's a crap pedal; that's why I want to work on this one before I tackle a few other older pedals that I have that need to be checked out. If I screw this one up it's no sweat so it would be a good pedal to begin the journey on. If I get it fixed I'll list it on Ebay with all of the others that are being listed for $90+ and make a little on it. Or maybe I'll just keep it. I dunno.

I'll check out that site though; thanks!
 
An audio probe is really nothing more than a cable with a capacitor in series with the tip. The sleeve connection goes to the pedal's ground, and you poke around with the cap to listen without having to worry about DC conditions. Google it real quick.
 
LM386 Audio Amplifier Kit (#1695) | NightFire Electronics

First build that^, you can probably find a more local source of the kit. There are shedloads based on the LM386 chip. This will form the amplifier basis for an audio signal tracer. Run from just 3 volts, 2x AAs. the chip will give you plenty of volume into any cans. With a 9V supply it will give a good account of itself on a speaker and will be surprisingly loud thru a guitar speaker such as a V30.

Dave.
 
ecc83 said:
LM386 Audio Amplifier Kit (#1695) | NightFire Electronics

First build that^, you can probably find a more local source of the kit. There are shedloads based on the LM386 chip. This will form the amplifier basis for an audio signal tracer. Run from just 3 volts, 2x AAs. the chip will give you plenty of volume into any cans. With a 9V supply it will give a good account of itself on a speaker and will be surprisingly loud thru a guitar speaker such as a V30.

Dave.
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This is a dumb question but bear with me, I'm a novice when it comes to doing more with electronics (outside of changing guitar pickups)... What exactly is the purpose of the kit in your link; just to gain experience with PCBs, etc? Or is it a tool to help work on the pedals? Again, it's a dumb question but...I'm clueless. :o
 
pikingrin said:
This is a dumb question but bear with me, I'm a novice when it comes to doing more with electronics (outside of changing guitar pickups)... What exactly is the purpose of the kit in your link; just to gain experience with PCBs, etc? Or is it a tool to help work on the pedals? Again, it's a dumb question but...I'm clueless. :o
Click to expand...

Bit O both. Building that simple amp WILL hone your skills but more than that it will give you the basis of a signal tracer which is nothing more than an amplifier with a lead on the input so arranged that you can connect it into various points of the circuit under test (c.u.t.) and listen to the progress, or not, of the signal.

Once built you can easily test the amp by connecting cans to OP and a guitar to input, makes a very passable headphone practice amp.

If you are still stuck I can draw you out a diagram the morrow?

Dave.
 
ecc83 said:
Bit O both. Building that simple amp WILL hone your skills but more than that it will give you the basis of a signal tracer which is nothing more than an amplifier with a lead on the input so arranged that you can connect it into various points of the circuit under test (c.u.t.) and listen to the progress, or not, of the signal.

Once built you can easily test the amp by connecting cans to OP and a guitar to input, makes a very passable headphone practice amp.

If you are still stuck I can draw you out a diagram the morrow?

Dave.
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I see that the kit in that link has RCA terminals; would I be able to use the leads from my ohm meter to use it to do whatever it does? (That statement most likely proved how inept I am when it comes to this stuff... I'm going to start reading up on some idiot's guides to circuits :D.)

I guess my main question would be, in regards to that kit, is that something that I will need to check the components on the PCB of that pedal?
 
It's just an amplifier. You might be able to use the probes from your multimeter, but it would take some messing around. Unless you really want the practice, you can use anything else that you have available to amplify the signal for diagnosis. Just "build" a quick audio probe and plug it into your amp, or the instrument input on your interface, or whatever. Use it to follow the circuit from the input until the sound goes away. That gives you a good idea of where to look for a fault. With an intermittent problem like this, I'd guess that actual voltage readings taken with your meter will get you closer faster. Your description kind of sounds like something misbiased somewhere, but it's tough to say without those voltages.
 
Just to be clear, and make sure we're all talking apples-to-apples here... Would that probe do anything to help me diagnose the problematic components in a guitar effects pedal?
 
Theoretically yes. Like I said, you poke around with the probe while listening through whatever you've plugged it into, and preferably while referencing the schematic. Start at the input jack and follow through to each component until you find a spot where you should be getting sound and don't. Then, it's a safe bet that the problem is very close to that point.
 
Or...Buy a 'scope!

Actually there are one or two quite useful free scope apps around for PC. Need a decent soundcard and a "safe" buffer amp tho, especially for use on valved gear.

Dave.
 
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