Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all, amazing to see that this thread is still going!!!

My pair of M1 Active 620 are still going strong after repairing them based on the knowledge in this thread back in 2018! But I also have a pair of M1 Active 520 (the original, not the USB) and one of the pair has the LED on but no sound. I've opened it up but it has a totally different power supply based around a toroidal transformer. Had anyone repaired one? Should I start another thread for it as it's a different design?

Re: Repairing Alesis M1 Active mk2 Monitor Speakers



I agree that moving it closer would be better, but I'm not convinced that the inductance of the component legs would make that much difference. The UC3844 datasheet says this about pin 7: "A bypass capacitor, typically 0.1 μF, connected directly to GROUND with minimal trace length, is required on this pin. An additional bypass capacitor at least 10 times greater than the gate capacitance of the main switching FET used in the design is also required on
VCC."

The cap with minimal...

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

By the way... having spent a fair bit of time studying the schematic for this power supply, I still don't understand some parts.

One of these is how Q2 gets turned on. Is it T2 that drives it? Or is it a pin 3 of T1? And what does Q5 do?

The other grey area is the circuitry below U1 on the schematic. I'm guessing that Q6 is opened by RT2 if Q2 overheats, which would disable the PWM output by forcing pin 1 of U1 to ground. What do D15, Q7 and C35 do? Do they implement some kind of slow startup by charging...

Re: Repairing Alesis M1 Active mk2 Monitor Speakers



I opted for leaving the legs of C8 as long as I could (the full length of the shorter leg or about 2cm), and bent it well away from R3 and R4, almost into the gap between the heatsink and L2. I've also replaced the 37k resistors with 47k ones on the board I've repaired, which should make them dissipate about 20% less power. Even next to the heat source the original C8 cap lasted for over ten years, I can live with that ...

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all, just popping in to stay thanks to everyone who has contributed to the information in this thread (especially Khron ).

I was able to resurrect my M1 620 which has popped its fuse. It took two tries before I came across it and I'm still not 100% sure but I think replacing U1 did the trick. R3 and R4 had burn marks so this time I've also replaced them as well as cleaning the burned up glue that partially covered them. Fortunately I didn't lose any traces. Before replacing U1 and the two resistors, I've replaced...

Re: New Members - please post your introductions here

Hi all, thanks for this awesome forum. I have just fixed my Alesis M1 Active 620 thanks to the information in this wonderful thread: [url]https://www.badcaps.net/forum/showthread.php?t=10910&page=15[/url]

Cheers,
VikRe: New Members - please post your i...<br /> Cheers,