Intermittent Problems on Modded Pedals Question

[vmazz38]

Measuring across R1 I get 2.4 volts and gradually climbs to 3.5v. So ther is definitely something pulling current so that voltage is being lost there? What would be the usual suspect? Bad joint? ICs trannies  or caps?

[R.G.]

Measuring across R1 I get 2.4 volts and gradually climbs to 3.5v. So ther is definitely something pulling current so that voltage is being lost there? What would be the usual suspect? Bad joint? ICs trannies  or caps?

Ohm's Law tells us something. The voltage across a resistor tells you the current. Your 120 ohm R1 shows a current of I = 2.4/120 = 20ma, climbing to I = 3.5/120 = 29.2ma.

That's actually not too big, as many pedals are in the 10-30ma range. It's quite odd that it climbs. Are these voltages measured with the LED indicator on or off?

[vmazz38]

The LED was on when taking those readings.
Do you think the pots could be an issue? I had read there were some issues with these pots. I had unsoldered and measured a couple but they were spot on with resistance and did not give me any odd readings so I put them back in.

[vmazz38]

I was able to take readings when the pedal was working(effect was clear and strong). And the voltage drop was nearly completely gone. About 9.3 volts at the DC Jack+ interestingly at D1 where there had been about .8v read across the Diode before, now when the pedal was working it was practically nothing .02v, does that mean anything? I am basically to the point where I know that the voltage loss is the primary factor I lose the effect sound, it manifests in different ways, no signal passed,scratchy signal passed, or effected  signal passed. But I still havent figured if the loss ov voltage is due to a bad joint or a component.

[R.G.]

I was able to take readings when the pedal was working(effect was clear and strong). And the voltage drop was nearly completely gone. About 9.3 volts at the DC Jack+ interestingly at D1 where there had been about .8v read across the Diode before, now when the pedal was working it was practically nothing .02v, does that mean anything?

It means the current through it was very small, not enough to fully turn on the diode. This is a fit with the "change in current makes a change in power supply voltage" theory.

I am basically to the point where I know that the voltage loss is the primary factor I lose the effect sound, it manifests in different ways, no signal passed,scratchy signal passed, or effected  signal passed. But I still havent figured if the loss ov voltage is due to a bad joint or a component.

I remember you saying you remelted the joints. It's unlikely to be a solder joint if you did that well.

My best guess is that there is a component with an internal flaw that lets it eat a lot of current intermittently.  Does the failure still happen reliably when you press or poke what you did before to make it happen?

Suspects include:
- an older electrolytic you didn't replace
- an electrolytic that has a pin spacing different from the PCB that was shoved into the PCB anyway, stressing the internal joints
C1 and C13 are good suspects for this, as they're in positions where if they went conductive, they'd pull about the right amount of current, maybe.

- then the rest of the universe...    That is, I'm out of good guesses.

From here on, debugging will rely on tracking down where the excess current is going. There are two ways to do this, one that's quite intrusive on the PCB, the other requiring a highly specialized voltmeter.  Neither are pretty. Well, you could use a hall effect probe to sense the current flowing in a trace by its magnetic field, but that's tricker still.

[vmazz38]

Again, I want to let you know how much  I greatly appreciate your time RG. 
As you may know im dealing with a pedal which can be bought used on eBay for about 25-50$.
But i've invested time and effort into this one so im kinda being persistent on getting this one going. (I may ultimately abandon it and get a used one and do the mods again.)
One last question.
As ive gone over this PCB so many times and used some flux , as well as flux remover, it appears pretty clean, but I wonder about flux conducting across traces. Your thoughts on flux and residue?

[R.G.]

I very seldom worry about flux residue. Sure, it's bad for long term life, but only for very long term life, and then when it attracts and holds dust and other junk that absorbs atmospheric water.

But then I'm always using rosin or very lightly activated rosin flux. Highly activated flux, water soluble flux or any of the plumbing or other fluxes are corrosive if left on. The "no-clean" fluxes are variants of rosin that is non-conductive and non-corrosive at normal temps.

Isopropyl or ethyl alcohols are efficient solvents for rosin based fluxes, so get out the bottle of rubbing alcohol and a dispose-able toothbrush and go after it. I wouldn't use the Vodka or pure grain for this, although they would be very good at it.   

But I don't think flux residue is your problem.

[Gainiac]

I know this topic is old but based on my research this problem seems to be widespread with Arion pedals so for posterity sake I wanted to get the word out that a manufacturing defect with some of their boards left some microscopic cracks in traces and this is the source of the intermittent fading out of the effected signal.  It can be diagnosed using "freeze" spray (gum remover, compressed air, etc) by spraying small areas on the back of the board while feeding audio through the effect and listening for the wet signal to come back in the output. 

On my SCH-1 chorus, the problem was in the pad for the middle leg of the bias trimpot so that might be a good place to start.  That's all, carry on.