Looking after the problem
Inside we see the usual configuration with single power/inverter board and single signal board. It is safe to assume the problem is on the power board, so undo three screws and unplug the cable connecting it with the signal board. And remove the insulation film too.
As expected, most of the capacitors are bloated. In this case, the worst is the +5.1 V stand-by rail, because of that the unit was not able to get even to the stand-by mode. The original caps are some C(r)apXon, I have replaced all of them as even the good ones will fail soon anyway.
This board in the 931BW is still the same concept as Samsung used in dozens of different models: A single multi-pin TO-220 PWM IC with integrated transistor on the primary side. On the secondary we have +5.1 and + 15 V rails, in this case both using pair of DO-package diodes. Notice there are also spots for TO-220 diode and heatsink, for different version of the board. The inverter uses dual transistor in single package. It is also possible you will find a different board inside as many of them were interchangeable.
Capacitors have been replaced with two KZN 1500 uF/6.3 V and a single LXZ 1000/6.3 from my stock. They are only D8 but still much better and with higher capacity than the original D10 caps. The remaining three are KYA 1000/25. If nothing else is available, you can use quality 16V caps as there is only 15 V there, but 25V capacitors are safer choice. The remaining two have been replaced with KMG 1/100 and KZM 47/35, if I remember correctly. I have also added the missing MOV (HEL-10D391K).
After reassembling and mounting everything back together, the SyncMaster 931BW runs like a charm!
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