SOLVED Dead EHX Small Stone

[giovanni]

I got a Small Stone from a coworker for free. It’s completely dead: no sound and not even the LED turns on. I opened it up today and couldn’t find anything obviously wrong inside. The foot switch seems to work and then components and solder joints look good.

However I noticed that there is DC voltage on the output and on other spots in the circuit so my guess is that there is something wrong with the power section. I haven’t looked at the schematic yet but I wanted to ask for advice on how to proceed. What could be broken? Could a busted LED cause this? I ask because I once burned an LED in a pedal and it stopped working, then I replaced it and it was fine.

Any suggestions are appreciated!

 

[jwin615]

I have been using a battery because I don't have a 3.5mm adapter at the moment. I have no idea how old it is, the guy who gave it to me didn't give me any information. The mod in the picture above looks like the one I have so I am gonna assume that's not the issue.

About the schematic version: there is a code on the PCB but I can't find anything online about it.

I'll do some continuity tracing next. Probably next weekend since I can't today and am traveling for work next week. Thanks for the help guys!

I'd recommend fudging around the EHX forums as well. Ya never know. Something to do in the hotel room anyway. Safe travels.

 

[chris.knudson]

Is this shorting out?

 

[giovanni]

View attachment 70941
Is this shorting out?

Nope. Check the other picture!

 

[chris.knudson]

Nope. Check the other picture!

Yep. I see that now.

 

[Cybercow]

Camera angles are important. I had to look a long time to find "that added resistor" . . . .

 

[giovanni]

Ok I tested the foot switch outside of the pedal and it seems to work fine. I also disconnected the LED in case it was creating issues, but that was fine. The true bypass mod looks correct.

My guess is that one of the caps is busted and causing the problem, but without a verified schematic I’m gonna have to guess which one.

 

[giovanni]

OK I realized my testing setup was incorrect. When using a battery, one needs to plug a jack in otherwise the battery ground is lifted. When testing voltages, I connected the negative lead to the battery negative lead and then using the positive lead to test. All the tests conducted this way were reading Vcc. I’m not sure why that I but once I connected the ground of the battery to the pedal I started getting more reasonable voltages all over the place. So now I can do some actual troubleshooting of voltages and whatnot. I’ll start from all ICs and transistors and report back. And if anybody has any insight into the weird reading I was getting before, I’d be curious to hear it!

 

[Cybercow]

OK I realized my testing setup was incorrect. When using a battery, one needs to plug a jack in otherwise the battery ground is lifted. When testing voltages, I connected the negative lead to the battery negative lead and then using the positive lead to test. All the tests conducted this way were reading Vcc. I’m not sure why that I but once I connected the ground of the battery to the pedal I started getting more reasonable voltages all over the place. So now I can do some actual troubleshooting of voltages and whatnot. I’ll start from all ICs and transistors and report back. And if anybody has any insight into the weird reading I was getting before, I’d be curious to hear it!

My best guess is that with ground lifted at the input jack, the readings would all be Vcc because there was no completed ground for the effect portion of the circuit, and while the negative lead of the DMM was connected directly to the battery, the DMM would always read Vcc as the DMM was completing a (measurement short) circuit, but not for the effect circuit itself.

 

[giovanni]

My best guess is that with ground lifted at the input jack, the readings would all be Vcc because there was no completed ground for the effect portion of the circuit, and while the negative lead of the DMM was connected directly to the battery, the DMM would always read Vcc as the DMM was completing a (measurement short) circuit, but not for the effect circuit itself.

Yeah I was wondering if it was something like that. Oh well, at least this means progress!

 

[giovanni]

Alright I think I sorted this out. The LED was never working so I disconnected. Then I plugged in the pedal and it now works perfectly fine! I’m not surprised btw, once I fried an LED in a pedal and the sound was gone.

Well, I had never played one of these so I have no idea whether it sound exactly as it should but it sounds good to me. Maybe I’ll record a quick sample and you guys can tell me. The two colors are quite different from each other which I did not expect (one very dark and the other very bright, both usable). I haven’t had time to replace the LED (the kids are demanding a snack right now) but once that’s done I’ll call this a win. Not too bad for a free pedal!

And thank you all for the help!

 

[Cybercow]

Glad you're sorted it.

 

[giovanni]

Removed the LED and measured it out of the circuit and it checked out. So I have no idea what was wrong with the pedal but it is fixed now.