Odd effect pedal issues over time.. what gives?

[joelap]

Anyone ever have problems that develop over time?  I had a ce-3 that would start making popping noises after 30 seconds of receiving power.  Another pedal the led would stop working after it had been working fine for a given amount of time... now I've got another modulation pedal... works fine when i turn it on, but leave it on for a while and it stops modulating!  I reheat solder joints, it works again... then magically over time stops modulating again!  Its baffling... how can something work perfectly, and then after some seconds or minutes, stop working?  I could see if a wire was cracking off slowly or something... but thats not the case here as I've reheated those joints and even replaced wires. 

Of course, I did two of these pedals; one for myself, and one for a friend... guess which one is working?  My friend's of course

[markm]

Bad Cap? 

[joelap]

hmmm... thats a good possibility.  I'll look into it, thanks!

Interestingly enough, the problem with the LED going in and out over time was solved by removing the socket I had in place for the resistor controlling the brightness and just soldering the resistor I had in place! 

[R.G.]

In analog electronics, there's only a few ways you get changes over a time scale of seconds or more.

The most common are a cap charging through a large resistor. For instance, a resistor you thought was going to be much smaller. Or a cap that's unexpected bigger than you think. The commonest "pops until it's been on for a while" scenario is when you have a 10uF or so input cap and a 1M or greater pulldown resistor. The time constant of that combo is 10uF*1M = 10 seconds. So the input will cause popping for maybe 20 seconds. A bad socket can make a small resistor suddenly be a huge one through high contact resistance.

Then there's heating. Anything in the range of several seconds and greater is usually the result of something heating up.

[RickL]

That sounds exactly like the problem I have with an old EH Echoflanger that I bought several years ago. It worked fine for the couple of minutes I spent trying it out in the junk store I found it in but when I got it home and spent some time with it I found that the wet signal would start to distort and then finally fade completely away over the course of several minutes.

Briefly shorting V+ to ground would bring the effect back for a short time but it would fade out quicker than the first time. If I left it sit for several days I was back to the origional response.

I never did figure out what the problem was and it still sits in my "I'll get to that someday" pile.

[frokost]

As explained here, http://www.diystompboxes.com/smfforum/index.php?topic=61357.0 I too have a problem developing over time. Replacing all electrolytics almost solved it though. I would really like to know what else may cause this. Perhaps heating, as R.G. suggests?

[R.G.]

A really leaky cap will self-heat from the leakage, like a resistor.

[Paul Marossy]

A really leaky cap will self-heat from the leakage, like a resistor.

Huh. That's a good one to know! 

[frokost]

Can normal caps be leaky too, or is it only valid for electrolytics?

[joelap]

In analog electronics, there's only a few ways you get changes over a time scale of seconds or more.

The most common are a cap charging through a large resistor. For instance, a resistor you thought was going to be much smaller. Or a cap that's unexpected bigger than you think. The commonest "pops until it's been on for a while" scenario is when you have a 10uF or so input cap and a 1M or greater pulldown resistor. The time constant of that combo is 10uF*1M = 10 seconds. So the input will cause popping for maybe 20 seconds. A bad socket can make a small resistor suddenly be a huge one through high contact resistance.

Then there's heating. Anything in the range of several seconds and greater is usually the result of something heating up.

Interesting... however, in my case the popping occurs after 10 seconds or so, not before.  I'm guessing that leaves me with a) heating up or b) bad cap somewhere.  Its interesting in that when i run a soldering iron over all the connections, I plug it in and it works fine.  half a minute or so later, its like the pedal says "wait a minute... I'm not supposed to be working!" and goes all flippertyzerburts on me.

[R.G.]

... or, it could mean the cap is OK at power on and leaks down because it can't hold the correct voltage up.

[aron]

Normal caps can leak as well. I have a Silver Mica cap that IS bad, but I can't/don't know how to detect the defect with my Sencore Cap tester. It passes!

[mat]

I have easyvibe that has its depth almost full every time when the effect is engaged no matter where the pot is adjusted ? Moving the pot slightly puts it to the depth that the pot shows. Bad pot ?

[Paul Perry (Frostwave)]

I have easyvibe that has its depth almost full every time when the effect is engaged no matter where the pot is adjusted ? Moving the pot slightly puts it to the depth that the pot shows. Bad pot ?

Maybe the wiper is losing contact with the track inside the pot.
on the other hand, sometimes it seems that a pot is defective, but actually the track is broken at a pot pin (because pots take a bashing sometimes) and as you move the knob, the track break opens and closes. Sounds a physical problem anyway.