SOLVED Dead EHX Small Stone

giovanni

giovanni

Well-known member
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!

IMG_1681.jpeg
IMG_1680.jpeg
 
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From the 2nd photo, it appears the longer stompswitch jumper is in contact with the output jack connection - the purple wire on the stompswitch.
 
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giovanni said:
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!

View attachment 70783
View attachment 70784
Click to expand...
DC on the output leads me to think some lead shorting to output or a shorted blocking cap

Also curious from the pic- the big electrolytic cap close to the speed knob- is that just the board I’m seeing around it or did that cap leak out the magic schmoo that makes it work?
 
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Giorfida said:
DC on the output leads me to think some lead shorting to output or a shorted blocking cap

Also curious from the pic- the big electrolytic cap close to the speed knob- is that just the board I’m seeing around it or did that cap leak out the magic schmoo that makes it work?
Click to expand...
Oh good catch. I didn’t even notice. I’ll take a closer look later and report. Thank you!
 
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I looked a bit closer but I can’t tell. I can say for sure none of the other caps have that stuff. I’m trying to find the right schematic for this pedal to see what this cap does (it’s 220uF, so maybe power filter?). Maybe I’ll just replace it to see what happens.

Edit: removed and replaced but no change. The old cap measures 210uF, close enough.
 
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This pedal has simple power filtering, just a resistor (as I recall it is 100r) and electrolytic cap. I'd check first if there the pins of electrolytic cap are not shorted and the resistor is not damaged.
 
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Have you removed that dodgy 220uf filter cap, the negative side should be going to Ground, the positive should be going to the 47/100? ohm resistor which should be going to 9v power..
 
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giovanni said:
I’ll check that again. I thought it was ok.

Edit: Red herring
Click to expand...
Fair & good enough. Camera angle in the 1st shot was all then.

giovanni said:
Q5 has ~Vcc on all pins, that can't be right. The ICs are all getting Vcc on pin 7... and on all other pins... WTF
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If all the pins on the CA3094s have Vcc, and that includes the ground pin 4s on them, then there could be a lost/open ground somewhere.

giovanni said:
For sure. But I don't know if the pedal has every worked post mod, the guy didn't tell me. I do wonder what the deal is with that added resistor that looks like it's shorting R14 and R41.
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Can't make out what that added resistor is, but you should be able to lift one leg (you have a clear photo of where it goes if it needs to be replaced) and see what happens.

If that's not the correct schematic, you can verify by starting some continuity traces from the input thru circuitboard to the first component, measure that (may have to lift a leg), then rinse and repeat thru-out. That should lead you quickly to the first VBias measurement point between R2 & R3 on the schematic.
 
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Mcknib said:
How old is it? are you using the original power supply, back in the day some were tip positive if it's a 3.5mm power jack

Easy enough to check if it gets inverted voltage on the pcb power joints or dc jack lugs
Click to expand...
I did mention the power supply jack polarity earlier but it got wiped when I reposted the PCB with the original DPDT Switch.

Here is another PCB that has trimmers for a volume loss mod, I was only concerned with the true bypass switch wiring:

1710662267953.jpeg
 
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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!
 
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