Need some ideas on malfunctioning pedal

[birv2]

I moved this from another thread to see if some of the pedal wizards here had any ideas. Just got a used Digitech Screamin Blues pedal and encountered the following issue. Any suggestions?

Hmm.

Well, I got the pedal today and tried it out. I actually like the brightness, since my set up is very mid-heavy (even with the tone on the amp all the way up and my tone knobs on the strat all the way up, it's still pretty middy). So that's good.

However, there may be something wrong with the gain. If I crank it past half way, I got some serious static every time I hit the strings, sometimes drowning out the notes. If I dial it back below half, it doesn't seem to happen. I've experimented with different combos of level and gain, it either seems to give me the static at higher gain/levels OR I don't hear any gain at all.

Could it be a bad gain pot? Or something else? I want to try to narrow down the problem before I contact the seller.

I like the EQ so I'd like to keep the pedal but....

[tunghaichuan]

Bob,

You said you cleaned the pot, correct?

If that didn't take care of the problem, my next guess would be a flaky solder joint. The new RoHS lead-free solder is crap, there can be cold solder joints. Especially around the input and output jacks.

Can you return the pedal? Is there a guitar store that you can try out a new one to compare?

Keep us posted.

tung




I moved this from another thread to see if some of the pedal wizards here had any ideas. Just got a used Digitech Screamin Blues pedal and encountered the following issue. Any suggestions?

Hmm.

Well, I got the pedal today and tried it out. I actually like the brightness, since my set up is very mid-heavy (even with the tone on the amp all the way up and my tone knobs on the strat all the way up, it's still pretty middy). So that's good.

However, there may be something wrong with the gain. If I crank it past half way, I got some serious static every time I hit the strings, sometimes drowning out the notes. If I dial it back below half, it doesn't seem to happen. I've experimented with different combos of level and gain, it either seems to give me the static at higher gain/levels OR I don't hear any gain at all.

Could it be a bad gain pot? Or something else? I want to try to narrow down the problem before I contact the seller.

I like the EQ so I'd like to keep the pedal but....

[birv2]

Thanks, Tung. Yes, I used contact cleaner on the pot.

If it's a bad solder joint, would resoldering it fix it?

Fortunately, the guy I got it from is willing to undo the whole swap if necessary. I'd just like to be able to use the pedal!

[tunghaichuan]

Thanks, Tung. Yes, I used contact cleaner on the pot.

If it's a bad solder joint, would resoldering it fix it?

Fortunately, the guy I got it from is willing to undo the whole swap if necessary. I'd just like to be able to use the pedal!

Hmmm... DVM is more the pedal guy around here, hopfully he'll chime in. :poke:

If it is a bad solder joint, the best thing to do is "shotgun" it and reflow all the solder joints. This can be tricky with the new RoHS solder. It melts at higher tempertures than leaded solder so it is possible to cause more problems than it fixes. It is possible to overheat some of the components and damage the pedal further :( IMHO, the best way to accomplish this is to remove all the old solder and reflow the joints with brand new leaded solder. If you can't do this yourself, taking it to a tech can be expensive, much more than the worth of the pedal.

Another bad thing about RoHS solder is that the joints don't look shiny like leaded solder joints do. When I first started working with Chinese-made Valve Juniors, I couldn't believe that was the way they came from the factory. All the joints look cold soldered, but weren't :(

I hate to bring this up, but do you feel comfortable disassembling the pedal? You might want to do a visual inspection of the components. Maybe post some close-up pix?

tung

[birv2]

I feel comfortable opening the pedal, but won't be able to get to it till next week.

I've got a tech friend who's willing to take a look at it next week, so we'll see what he says. I agree, the pedal isn't worth too much work. Fortunately, as I said, the other party is willing to undo the swap.

I'll post here when I know more. Thanks for the input.

[tunghaichuan]

I feel comfortable opening the pedal, but won't be able to get to it till next week.

I've got a tech friend who's willing to take a look at it next week, so we'll see what he says. I agree, the pedal isn't worth too much work. Fortunately, as I said, the other party is willing to undo the swap.

I'll post here when I know more. Thanks for the input.

Sorry I can't be more help. :(

Keep us posted.

tung

[duhvoodooman]

I think the first thing I'd do is just replace that pot. I find I don't encounter bad electronic components very often, but the added mechanical element of a pot introduces a much higher probability of problems. I've had two defective brand new pots just within the past year, so this definitely can happen.

If that doesn't do the trick, then you might want to start reflowing solder joints, etc. And definitely do a general visual inspection while you're "under the hood".

[tunghaichuan]

I think the first thing I'd do is just replace that pot. I find I don't encounter bad electronic components very often, but the added mechanical element of a pot introduces a much higher probability of problems. I've had two defective brand new pots just within the past year, so this definitely can happen.

If that doesn't do the trick, then you might want to start reflowing solder joints, etc. And definitely do a general visual inspection while you're "under the hood".

It just occured to me that it could be a bad coupling cap to the pot. If it is leaking DC into the pot, it will get scratchy, maybe even some static on int. DVM's advice is good, replace the pot and I'd also replace any coupling caps going to the pot.

tung