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Discussion Starter #1 (Edited)
So I had a fellow forum member, u1-2go, reach out to me about attempting to repair his original 750's "blue" spu. It had a failed right turn signal and fast flash on the left signal, while also likely causing a stalling issue. It was worth a try and as of right now the repaired spu is on its way home.

There were no damaged traces on the board yet the board warped up like a pimple around the low beam headlight MOSFET. It also melted the solder and thankfully did not short to any other pins. I assume the MOSFET simply was experiencing thermal runaway from being sealed up. In fact, it turned the RTV that contacted it into a sticky tar-like substance. It was replaced for good measure and the board should be fine other than cosmetically. This was not related to the known problems but it was about to bar-b-q itself so good to have caught it.

As for the right turn signal, it too was melting the solder at the resistor (small red circle in the first pic) before it finally failed. The second pic also shows how ugly the low beam headlight MOSFET cooked the RTV.
 

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Discussion Starter #2 (Edited)
The right turn signal was an easy fix by replacing the resistor, I also replaced the resistor for the left turn signal for good measure. There are also two other resistors in the same area that work to prevent power spikes from the two mechanical relays, which I also changed because they appeared to have suffered overheating.

The small white mechanical relay controls the ignition coils, so the stalling could be due to anything related to that relay. To ensure against a bad solder joint, I re-flowed the solder on the relays. These two mechanical relays also produce the most heat into the board, so as a "hobbyist's fix" to keep the board cooler I attached a small heat-sink directly to the board opposite the white relay. The heat-sink I sourced sets perfectly flush with the back covering.

I also re-flowed the solder on the fuel injector MOSFET and "latching relay" MOSFET to ensure that a bad solder on either one was not causing the stalling.
 

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Discussion Starter #3 (Edited)
Everything seemed pretty standard except for the fast blink on the left signal. The cause eluded me for days...until by happenstance I noticed a "dot" on a transistor on the left signal circuitry. That dot was a burn mark, about half the size of a pen head. That transistor was also on the negative voltage line so I changed all 3 capacitors related to the inverter chip as a precaution.
 

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Discussion Starter #4
So after several hours over the course of about two weeks and a handful of parts worth <$20 the notorious blue spu should be failure free. Fingers crossed for the lifetime of the bike.
 

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Discussion Starter #6 (Edited)
Nice detective work Benjamin. Wow.
Curious do you then encapsulate the board again?
That would be a big NOPE. IMO, the board's design is too compact for the heat generated by the components, it needs air flow. I do seal the rear portion back to the board and after the front plastic cover goes on, the unit is fairly water resistant. It should be fine for occasional rides in the rain but not for being left out in the elements.

I use RTV to minimize vibration of the MOSFETs and through-hole resistors.
 

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Wow.... very impressive. Just getting the potting off the board to access the components is a job in itself.
 
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