Dunlop 105q Battery Explosion and Internals Question

[squishyH]

I've got a Dunlop 105q which I picked up used a couple of years ago, didn't have any issues with it but haven't used it for a while. I got it out again today to do some wahing and found it was dead. Assumed it was the battery so went to change it (I power most of my pedals with power supplies but not the wah since it lives off board) and found the battery in it had apparently exploded, with the cells popped out of the bottom.

No apparent damage to any of the of the pedal internals, so I tried it briefly with a fresh battery and it all seems to work fine, but now I'm concerned about leaving it with the battery in again. It looks much like pictures of 9V's exploded from being shorted, I'm not sure how that could happen though when it's inside the pedal.

I also noticed that the pedal has a couple of undocumented internal trim pots (in addition to the one which controls the bypass delay from the automatic heel switch, I know what that one does). I can't find any good documentation about what those do, some pictures and anecdotes have them hot glued over to prevent tampering but the trims in mine are left free and adjustable. Some people say they are to calibrate internal voltage and should not be touched, others claim that they control parameters of the PWM oscillators for hte effect and can be adjusted without risk. I haven't touched them without knowing, but I'm wary that with the pedal being bought used that someone before me may have messed with them and that could be related to the blown battery? Like I said, I can't find any reliable information on their function, photo included.

Has anyone else had a 105q blow a battery, and does anyone reliably know what those extra trim pots inside do?

 

[bass-shy]

If you're not using it often, I would just remove the battery when you have it stored.

As for the trimpots, I would recommend contacting Dunlop directly. Just include the serial number since there are probably a number of revisions.

Dunlop has responded quickly the two times I needed them and they were beyond helpful and professional to deal with.

 

[Real Soon]

I've worked with battery cells (at Energizer's R&D facility in Ohio) before, and learned a ton about what makes them last, wear out, and have unexpected end-of-life events.

If the pedal is buffered bypass only, that does mean the battery is technically on a closed circuit at all times, and were it to run out of juice as such, it could react by pressure building, dumping the electrolyte and forming potassium carbonate crystals.

Even batteries that wear out over time in natural, open-circuit circumstances can decide to overpressure as chemical changes happen in the cell and dump their electrolyte. Less common but not impossible by any means. Batteries are enclosures of chemicals and elements superimposed in approximately precise proportions.

As suggested above, I'd pull the 9V when the pedal's not in use, but the evidence doesn't currently point toward a circuit issue. Rock out with your wah out!

 

[squishyH]

Very helpful replies, thanks!
Interesting point about batteries wearing, I hadn't considered that buffered bypass circuits might cause more potential wear. I so rarely use batteries so I hadn't thought about removing it, at least that's easy with a simple snap on cover.

I'll contact Dunlop to see what's up with those trim pots, the PCB is dated to 2001 so it's probably a very old/early revision. If the pedal is unlikely to be at fault then I'm not worried though, when it's powered up and working it's fine.