Hi Grinder ,
the nearest Sieg board I've worked on is a FC250JSMD
the board looked like the laquer had been applied with a tar brush , nice and thick !
the only components I changed was some of the electrolytic capacitors
heat from the soldering iron freed the laquer so I was lucky
( 60 / 40 solder across both connections , I only use lead free when I have to)
my first thought would be to try cellulose thinners , but would test it out on an old computer board
to see what it does to the components , just incase !!!
take a picture of the pcb ,the markings may come of the board
if you remove the presets from board
you can wipe the dissolved laquer of the edge and away from the wire ended components
the only time I had a problem removing surface mount ic's
was when the red glue used to hold the ic's before soldering , worked too well,
the copper track come away with the ic
I would start with the easy bits first
change the through hole components first
the electrolytics and semiconductors in the + & - 12v power supply
since C12 decouples the +12v regulator
without the mains supply , it may be worth using a bench power supply set to +&- 15v to test the onboard regulators
and prove the ic's are faulty or not
to remove the ic's , I would cut the legs off first as close to the epoxy body as possible
with some high quality ,flush cutting side cutters or dremmel type of cutter
then you can remove the legs from the board one by one
If the laquer proves easy to remove
a soldering iron with a bit to heat all 14 pins would be quicker
the chip resistors are marked with three digits but the capacitors are not marked at all !
I'm not sure if the value of the chip capacitors is shown on all positions , on the circuits off the web
it looks like they are all 0.1 uF
NOTE :-- with your FC250BJ board
some of the resistors , setting the gain of some of the op amps will differ from the values on the FC350BJ boards
John