Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Well, that turned out to be a very good shout - a rub down with some IPA to clean up those points on the rear of the board and it's powered up and working perfectly!
I don't know whether to investigate further what might have caused the issue or just count myself lucky it wasn't anything more serious and keep my fingers crossed it doesn't happen again!
Now to investigate its slow starting pair to see if the caps there are indeed on their way out.
Thanks again for everyone's...
zinger5
New Member
Last Activity: 01-09-2023, 05:21 PM
Joined: 11-04-2022
Location: London
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Sorry for the delay - I didn't have much time today but I've managed to take some photos of the components on the board in the hope that might give you some clues at to what the issue might be. The only thing I've noticed on the rear of the board is a little corrosion (?) between pins 1 & 2 of the UC3844N. That's the close up picture of the rear of the board attached. Might that be causing a short or be an indication of the IC having sustained damage/worn out?
I'm aiming to test the voltages across those secondary...Last edited by zinger5; 01-04-2023, 05:14 PM.Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Ok, so here are the results of the first tests you both recommended - firstly R15 measured 0.2 Ohms on my MM so I think that is in range? R5 gave me a solid 10 Ohms and the diode D5 read 0.653 in diode mode.
As all of those sounded like they were probably in the right ballpark I moved on to testing D10-D13 - all of them read 0.468/0.469 on diode mode. Caps C17-C24 I tested in resistance metering mode and all gave the same figures - started at 0.2 Ohms and slowly climbed as the caps charged.
I should...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Wow, thank you both so much for your time and help! I'll work my way through those tests in the morning and will come back with an update on how it goes.
Thanks again,
JoeLeave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Ah, I was afraid you'd say that!!
I've just tested the working power supply from my other speaker and the resistance across the UC3844N pins are identical to the first one, so looks like that's just what my multimeter was reporting. However, the voltage across pin 7 and pin 5 is a nice constant 14.5V rather than the crazy fluctuations on the other board. Now I've tried powering up both boards side by side I can hear a very slight ticking every second or so from the defective one. It's really hard to pin down where...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Thanks - I'll disassemble the working speaker to see if that gives different values. My voltage across pin 7 to pin 5 seems in range- it's fluctuating between 11.1V and 14.8V every second or so, briefly stopping at 13V on the way. Is that fluctuation normal while the circuit is live?
Assuming the measurements on the working speaker confirm the theory, would I need to replace MOSFET Q1 as well as the UC3844N on this one?
Thanks again - it's really very much appreciated!!
JoeLeave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Hi Per Hansson - thanks for your assistance. I've just tested the UC3844N in the same way Skeeter did (neg probe on pin 7) and I've got some wildly different results! Do these indicate anything to you either with regards to that chip itself or others?
Pin 5 to 7 = starts at 10 Ohms, slowly rising reaches 70 Ohms after a minute. Kept rising!
Pin 5 to 1 = 34.5 Ohms
Pin 5 to 2 = 10.9 Ohms
Pin 5 to 3 = 0.9 Ohms
Pin 5 to 4 = 8.9 Ohms
Pin 5 to 6 = starts at 110 Ohms, rising...Leave a comment:
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Re: Repairing Alesis M1 Active mk2 Monitor Speakers
Hi all. Sorry to be resurrecting an old thread, but I've got a pair of Alesis M1 Active MkII speakers which are showing signs of some of the issues mentioned here and I can't seem to solve them. My right speaker is the biggest concern currently - until a few weeks ago it was taking longer and longer to come on after turning on the power switch but now it's refusing to start at all and the blue led flickers without going solid.
Having read through the whole topic it seemed most people were having issues with C8 and...Leave a comment:
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Re: New Members - please post your introductions here
Hi all,
I found my way here when trying to diagnose an issue with my Alesis M1 Active MkII speakers. Not the first by the looks of things!
JoeLeave a comment:
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