Identifying components and ordering replacements:
For some of the larger devices like the IGBTs it’s simply a matter of reading the id off the front and looking it up with a component supplier. For some others, like the varistor, you have to find the manufacturers datasheet and cross reference the marks on the device to the ‘part ordering code’ on the datasheet, then take that to the part suppliers
For the small SMD components it’s a bit more of a problem: the small 6leg devices on the PCB (Q7, Q8, Q9 and Q10) were all toast, as were D2 and D3, but these small devices have simple codes that are not unique – even if you know the make there’s no guarantee the manufacturer won’t reuse an identifier for different devices. In the end you have to look for devices that are physically the same and have the same markings then check the datasheet to see if they are a device that will work in the circuit.
For the diodes D2 & D3 (marked RPW 3d) this was fairly easy to guess they were back-to-back zenners, and if you ended up with something slightly different it wouldn’t matter too much, but these devices seem to be the right ones, RP designating 20v, W = made in china, and 3d indicated manufacturing date.
http://www.farnell.com/datasheets/1508362.pdf
Q7 - Q10 (marked 66C and b4) were eventually identified as dual fets (one n-channel one p-channel) which would work in the circuit, (DMG6602SVTQ) which according to the data sheet would be marked 66C and the B4 would indicate a manufacturing date of april 2014 - plausible.
http://www.farnell.com/datasheets/2814392.pdf
So the list:-
Part mouser no.
U1 634-SI8232BD-D-IS SI8232BD-D-IS Silicon Labs Gate Drivers
part farnell no. desc
Q1 -Q4 2781406 FGH40T65SQD-F155 FIELD STOP TRENCH IGBT, 650V/80A, TO-247 IGBT
Q7 -Q10 2061522 DMG6602SVT MOSFET, NP CH, 30V, 3.4 A TSOT23 dual n & p channel fet
D2, D3 2069380 BZB84-B20,215 DIODE, DUAL, ZENER, 0.3W, 20V, SOT23 back-to-back 20v zenner
D8 15v zenner >=0.5w
R13 7.5ohm
R9 15 ohm
0.5va 15v transformer x2