Trying to repair my ECU.

[AUSA66]

Use some sharp miniature pcb cutters cut the small legs off first if you overheat & try to remove you can tear the pad off the board.
Then use a nice hot iron & some solder to quickly heat the small legs & remove dont put the iron on the leg & let the iron heat up.
The parts will come off when ready dont try to force otherwise it will damage the pad they will take a bit of heat as the solder will be high temp to cope with the high temps .
Once you remove the 2 legs get the iron smoking hot then place on the tag of the transistor & apply the solder the solder should flow quickly allowing removal the trouble with the tap is normally they are soldered to a copper plane that uses a large area of the pcb allowing it to dissipate the heat
Sometimes the 2 small transistors beside it may be fried they are the drivers for the larger unit they are footprint SOT23 1 will be PNP the other NPN
The damaged unit is a 3055L n channel mosfet available from Mouser P/N 512-NDT3055L

 

[KitCarlson]

I have thought more about a fix. The main rework problem is soldering the tab on the sot223, due to the flex circuit bonded to enclosure heatsink. It is likely the circuit was infrared reflowed in a fixture prior to peel and stick to aluminum chassis. At solder time the thermal inertia would have been low for quick solder. Rework has two issues, getting enough heat to solder tab, yet avoid thermal damage to transistor, and adhesive that bonds flex to chassis.

A good alternative may be to just cut and remove small leads, then outboard a transistor. There are larger TO220FP package parts, that have an insulated package and also 10 times the power handling. With a single 4-40 screw, mounted nearby inside the chassis, and wired to small lead pads.

The use of the sot223 package in the original designs was risky. Just seems enough for a high impedance fuel injector, but no safety factor for a defective (shorted coil) injector. The photos in the post shows components shifted in the solder process. That may have happened if the fixture was bumped in the process, or too much solder paste was applied, floating parts. Too much solder also would increase thermal resistance, leading to early failure.

 

[AUSA66]

I have thought more about a fix. The main rework problem is soldering the tab on the sot223, due to the flex circuit bonded to enclosure heatsink. It is likely the circuit was infrared reflowed in a fixture prior to peel and stick to aluminum chassis. At solder time the thermal inertia would have been low for quick solder. Rework has two issues, getting enough heat to solder tab, yet avoid thermal damage to transistor, and adhesive that bonds flex to chassis.

A good alternative may be to just cut and remove small leads, then outboard a transistor. There are larger TO220FP package parts, that have an insulated package and also 10 times the power handling. With a single 4-40 screw, mounted nearby inside the chassis, and wired to small lead pads.

The use of the sot223 package in the original designs was risky. Just seems enough for a high impedance fuel injector, but no safety factor for a defective (shorted coil) injector. The photos in the post shows components shifted in the solder process. That may have happened if the fixture was bumped in the process, or too much solder paste was applied, floating parts. Too much solder also would increase thermal resistance, leading to early failure.

That,ll work used that method on my Fast ECU for the fuel pump drive used an irfp 450 TO247 package with an insulator washer no problems since