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Old 11-06-2014, 08:18 AM   #101
kerveras
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

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Originally Posted by Ozyris View Post
Well, the weeks have flown. I had a whole lot of stuff I needed to attend to so was not able to proceed with this project. But now the time has come to conclude my story.

I have finally completed the damage-bypassing and component-replacement exercise on my blown speaker, guided by the wise men who advised me on my journey with particular gratitude to Khron666.

Here is what the back of the board looks like now.


The cleanness of the result is deceptive. I have replaced at least 15 components. You can see the hole through the board where the explosion burnt it. There are three places where this happened, this one being the worst.

If you want to know what I had to go through to reach this point, please read back. I have in fact documented the entire exercise photographically. If anyone thinks it would be helpful to have this story visually online let me know and I will put it all on a webpage and link to it from here.

So the outcome? Today I finally assembled the board back into the chassis, cutting a hole in the metal sheet for the 2W resistors to poke through, and fitted it all back into the cabinet.

Tentatively I connected it up and turned it on...

It works perfectly. Who would have thought?

Thank you again to everyone who helped me with this. Specially Khron666.

Great site!


Hi i read through all your posts but you didnt specified or better i didnt understanf which component was causing the short.I already replace C8 D1,D2 check all the other Diodes checked MOSFET Q1 Q2 RT1,RT2 Zened diodes and still nothing.Its burning the fuse instaneous.Pls helppppp my email is KERVERAS@GMAIL.COM.Thanks in advance for your time.
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Old 11-06-2014, 10:04 AM   #102
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

How have you checked those components?

Are D3 and D4 ok? What about the primary caps?
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Old 11-06-2014, 01:02 PM   #103
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yap i checked all the diodes.After getting desperate i recall the big force my father who discovered that when i put back the MOSFET Q1 i left behind the heat sink that's why it was short and burning the fuse .How silly i am i know know.Capacitors all checked so probably is ok but i would have to assemble it and test to be sure.Guys you were a great help until now thanks again.I will post back when it will work .
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Old 11-07-2014, 02:03 AM   #104
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok guys the speaker looks ok.I apply Power the fuse is ok blue led ok.I didnt test the sound yet.Ok so i replaced D2,D4 and C8 that were faulty.I checked all the MOSFET and they were ok.My problem was solved with only the D2,D4 and C8.But because i forgot to put back the little rubber behind the MOSFET Q1 Drain was earthed and keep blowing the fuse and burning again the DIodes.When i put back the rubber on Q1 and replacing the diodes everythink was ok.So as far of what i read in the forum my case was easy but due to my fault made it complicated.
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Old 11-07-2014, 05:26 AM   #105
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Glad to hear you managed to track down the ("new") fault, and that it wasn't anything (more) serious

If the electronics don't "hiccup" anymore, the speakers should work fine now
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Old 11-10-2014, 03:59 AM   #106
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

well still have my board and speaker stoped for a year now , quit making music because of it , well also not much time due to repair buts, miss my studio !
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Old 11-13-2014, 05:44 PM   #107
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Had one in just today. The one i repaired only had a minor fault, one of the HV pins on the transformer managed to touch the metal plate under the PSU. There is adequate clearance but no insulation between the PCB and the plate, so a short is possible if a piece of metal falls inside, for instance.

Casualties: Two diodes in the rectifying bridge, the NTC and the first input filter burned up (owner tried replacing the fuse first, only to be greeted by a puff of smoke). Replaced these parts and put a new fuse in, monitor works great once again. I have also added a plastic insulator under the PCB to prevent this from happening in the future.
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Old 11-14-2014, 06:21 AM   #108
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Expect it (and its brother) for a re-cap, in the (near?) future...
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Old 11-14-2014, 05:03 PM   #109
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yeah i did notice it's full of Jun Fu... But there's A LOT of them in there for that size PSU, so they oughta last a while.
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Old 11-15-2014, 05:51 PM   #110
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well, depending on which revision PSU it has - "1st gen" has the start-up cap right "on" the heatsink and it WILL buck the kicket :P
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Old 04-14-2015, 10:44 AM   #111
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

can i replace c35 (50v 1mf) with 50v 47mf? thats the closest value i could find on some donor psu. i have replaced the big caps, r4 r3, and c8, still my speaker is lacking power, after a few minutes it warms up, and plays fine. what else? the fet's? no signs of damage on parts
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Old 04-14-2015, 02:02 PM   #112
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

loss of sound about 80% when volume pot at 5, then as i crank it up to 7-8 something pops, and volume goes up to 100%

Last edited by foxes; 04-14-2015 at 02:44 PM..
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Old 04-15-2015, 04:25 AM   #113
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Assuming you own a multimeter, let the bad speaker cool down, then check the supply rails after turning it on again. The woofer amp supplies should be in the region of +/- 30-35V, and the tweeter amp rails, around +/- 25V or so.

If something pops as you turn the volume control, that would point towards a busted pot, i think
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Old 04-15-2015, 10:38 AM   #114
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

-v_lo -22V
+v_lo 18V

-v_hi jumping between -23 -29
+v_hi 36-38

also a audible click every 2s, can't pinpoint location, one of the two smaller transformers marked L1 L2
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Old 04-15-2015, 02:21 PM   #115
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

That's starting to sound like the power supply's "hiccuping". What (brand/series/value) cap did you replace C8 with?

Are the rectifier diodes all ok? And the switching FETs?
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Old 04-15-2015, 03:13 PM   #116
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

VISHAY BC COMPONENTS MAL213661471E3 CAP, ALU ELEC, 470UF, 50V,

visually everything looks fine, i have bought new switching fets (irf840), i will replace them .
thank's for your help, this is way too complicated for me to diagnose
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Old 04-16-2015, 09:54 AM   #117
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

replaced irf840's nothing changed, diode bridge is fine, i think
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Old 06-02-2015, 07:50 PM   #118
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Guys you're the best! I have only one question: I need D5 Zener diode characteristics (voltage etc) to fix my M1 Active 620. Please if anyone has service manual or something, I can not find the Psb scheme for 620 I only found for MK II. Thank you in advance, any help is appreciated!
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Old 10-01-2015, 09:28 AM   #119
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Unhappy Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all, confronted with the problem of power Alesis MK1 active mk2.

I have a similar problem blue LED flashes.

I mentioned at the beginning of the capacitor C 35 and C8. Monitors work one day :-/ . Later I replaced capacitor C6 and C7. Again ALESIS has one day

Capacitors look good.

Where is the problem? :/
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Old 10-01-2015, 02:52 PM   #120
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

What did you replace those capacitors with?
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