Same issue for me, M1 mk2 actives that after pretty much exactly 5years packed in.. 1st one a month ago, blinking light first with very frequent intermittant sound then with a slow bass pop and squeal.. turned it off! Next yesterday the other one started blinking and no sound. Searched a few forums and C8 capacitor kept on coming up, opened them up - no visible signs on C8 to show it had packed in. only underneath the transformer PCB the offending hot resistor R4 and another one on other side had slight dark scorching on bottom of board. So thought worth a try at DIY, went to Maplin - I think they were £0.20 each! They didn't have exact same capacitor, so got 220uF 50V high heat 105, which helpful tech said shouldn't affect it at all.
A bit nervous as hadn't soldered in years and was quite tricky for a novice to cleanly remove the existing solder and cap. But with some reading up on how to's to remove capacitors and resistors cleanly - tip is apply new solder on to the pin first then it will help melt the original solder, and very quickly whilst its still molten use a spring vacum solder remover and hey presto it sucks up all the new and old solder leaving a clean hole with pin.(my first few attempts without applying new solder started messing up the board and thought id wrecked it but it was ok) Once id sussed this method, the second monitor was disassembled,new cap soundly in place and reassembled in 15 mins! Next gingerly plugged one back in.. expecting a mighty pop but was fine and sounding like new, next other one plugged in and its perfect too.
So it really is the cure.. totally chuffed now as saved me ££s For anyone never soldered before its probably best to learn how to remove old solder on an old pcb with new and then resolder an old cap or resistor in again other wise you could mess up the board quite easily.
One thing that may have aided mine to fail may be that they haven't really been turned off in 5yrs, my understanding was that with pro audio circuits it's the on/off power surges that ruin them.. but in this case if they had been off 70% of the time would this have saved them? Does anyone have any knowledge or thoughts on this, though I think i'll be turning them off when not using now to save the capacitors getting unessesary hot and drying out. But then I did read somewhere that they were manufactured with a 5yr lifespan.