In addition to empeg players, I also sometimes repair automotive ECUs (Engine Control Unit, aka "the car's computer").
Usually it's just a matter of somehow opening up the factory sealed enclosure (if possible)
and then looking for obviously fried components. Replace the baddies and eight times out of ten it works again.
The current one I'm looking at had an obvious failure point, in a 20-pin driver chip (CAD$8 from Digikey.ca). But getting it off the board was a real tug of war. In the end I just cut it into pieces, and pried those off to reveal the solid copper heatsink base of the chip, soldered to a very large pad on the board under the chip.
The soldering iron was inadequate for removal, so I applied heat from a small butane torch directly to the copper remnant of the chip, and it came away cleanly.
Obviously I cannot rely on the same method for reattachment, so I'm finally getting a hot-air (de-)soldering gun. Essentially a small heat gun with temperature and airflow controls.
I don't have it yet, but this is what I ordered:https://www.amazon.ca/gp/product/B07FBGFT3K/
There were several similar models, with various inclusions and exclusions, but I chose that one for the digital display and the calibration button, which should allow better temperature accuracy in conjunction with my multimeter and a temperature probe. There were other models ranging from around $25 upwards.
Anyone else here have experience with these things? Tips and advice welcome!