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Fulltone Supa-Trem pedal only works when it's cold?


Jeff R

Question

Okay, here's a bizarre one. I bought a minty clean Fulltone Supa-Trem ST-1 off the local Facebook marketplace, I mean minty, box, factory manual, even the little Fulltone sticker. I get it back to my shop, works beautifully that night, gorgeous vintage Fender BF tremolo tones with more versatility. Played it all night.

Next day, I go to show it to a client and it's not tremoloing. It's lighting up, signal is passing like it's bypassed, clean, no clips or bad distortion or hih/low vol spikes. Power light clicks on off, hard/soft LED clicks on off, speed is controlling the flicker of that LED, everything working great, just no bup-bup-bup-bup.

I go to use it that night, it works fine. Go to use it the next day, working fine. Later in the day, not working fine.

I finally figured out that it seems the catalyst of what's apparently intermittent tendencies is the temperature of the room. I keep my repair shop hovering in the high 60s most of the time. But I turn off the air when I'm soldering (my station is by the blower) or if I'm simply cold. It seems if the room goes above 70 degrees, the trem function no longer works.

What you guys think? Bad solder joint that's ever so slightly expanding or shrinking just enough to crap something out? An iffy chip? or what are they in nice old skool trems ... photo sensors?

I haven't reached out to Fulltone yet, you can't call or direct e- them anymore unless you provide video of your problem. Until I make a video showing my thermostat haha, what y'all think?

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Stick in in your shorts and see if that help? I'd put it on the soft setting first. LOL 

If it is true that is temp sensitive, its a photocell issue. My vibe was temp sensitive but to the point of not working, just sounded different. 

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Check it?

PHOTOCELL TRIMMER: There is a trimmer inside the pedal that we carefully set to get the optimal sound and feel from this tremolo device. There’s no need for you to touch this trimmer! If it is turned CW the current to the photocell’s LED is increased, which can intensify the tremolo effect up to a point. Turning this trimmer CCW will decrease the tremolo effect. We mark the “factory setting” with a line or dot on the PCB, in case you adjust it and then want to return to the stock setting

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Yep, I tried every setting with the photocell trimmer when the pedal wasn't working, the trimmer had no effect on the working/not working thing.

 

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Emailed Mike Fuller just now. He replied, almost immediately I might add, "that's a new one, I gotta see this!" and asked me for a demo video. I lucked out and caught the pedal acting possessed just now, sent him a vid of it acting up intermittent with the wop-wop-wop-wop, with the shop at a cold-for-me 66 degrees. We'll see what Mike comes back with. 

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9 hours ago, Jeff R said:

What you guys think? Bad solder joint that's ever so slightly expanding or shrinking just enough to crap something out? 

That’s my guess... you can verify by opening it up and applying pressure on the solder joints with a pencil eraser tip

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Maybe the tremolo "bug" is faulty? But then I would think the LED wouldn't be flashing. Weird. It's always great when the guy who makes them is going "wtf"?

Hopefully you can get it solved, but I would think maybe it'll need a trip to Fulltone. I'm sure they'd like to know what happened and how, to prevent it from happening again.

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Would guess an intermittent solder joint or maybe a drifting component.  

Solder - magnifying glass to check for cold joints, hairline cracks. Maybe fractured leads.  Can reflow all joints and see what happens.

Drifting components - get freeze spray or compressed air in a can. If you might have an idea if what to hit first, try them.

Or an O-scope and check for no signal. Really helps to have a schematic.

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I sent it to Fulltone today for them to diagnose and fix. A kind tech guy, Tsuguto, who watched the videos I submitted said:  

It can be a bad photocell in the optocoupler, however it usually has to get really hot or really cold for it to behave like this.  Also it simply can be a broken solder joint somewhere in the pedal or a footswitch going bad.

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Just notified by Fulltone. Octocoupler faulty, replaced and pedal fully tested and OK, part $9, labor $15. Considering it was bought used and not under warranty, and considering they turned it FAST, I'm quite pleased.

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