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Old 08-25-2016, 06:28 AM   #141
Idiotbox
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all!

Inherited a set of these speakers from an old housemate who ran away to avoid paying rent. I'm a musician and haven't looked at a circuit board since A Level Physics ten years ago.
They worked for a while, but then one dropped out, and then the other. Now neither of them turn on at all (no light, no sound).

Figured it's finally time to get round to repairing them, but the main thing I've noticed is that the common issue (C8 proximity to resistors) is not possible on this board.
I don't know if these speakers are a more recent production than the ones commonly described in the guides here and on Youtube... I read through this whole thread and am still totally unsure.

On my board, C8 and the little blue C14 have swapped places.
So, C8 is between U1 and R24, and C14 is next to R3 and R4.
There is also only one little C14, instead of two like on this video: https://www.youtube.com/watch?v=ThjO7vlb79E


I have no idea what process I should be undertaking to fix the speakers then, as the video guides now seem inappropriate due to it being a different board!
I don't really know what to look for in terms of 'signs of damage' or anything. The big black power cylinders all seem to have flat tops (one is dubious, but more flat than warped).

Guessing I should start with the fuses? I can say with certainty that one of the fuse 'beds' needs replacing (the metal clips that hold the fuse in place are broken).

Thanks for any help, I hope you can excuse my extreme lack of knowledge!
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Old 08-25-2016, 06:50 AM   #142
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Edit to above:

C8 and C14 have swapped places, but I noticed that there *should* only be one C14. C11 is still in the normal place (so on my board, between U1 and C8).
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Old 08-25-2016, 12:49 PM   #143
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I know for a fact that i've mentioned encountering at least two revisions of the power supply board (or one pair i've had slightly differed from what's in the service manual)
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Old 08-26-2016, 02:45 PM   #144
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ahh, must have missed that. As I say, I have extremely minimal knowledge on this subject... only some patience! So some of the things I've read I haven't understood.

So currently I'm planning on replacing, and have ordered parts for:
C1 & C2
C8
C35
The two big guys
The fuses
The 4 diodes

I'm not confident I've got the correct parts though. I made sure that all the important stats such as V, A, temp, etc are the same, but my C8 and C35 replacements are definitely different physical sizes to the originals... Is this normal?

The C35: https://uk.rs-online.com/web/p/alumi...75462035305626

C8: https://uk.rs-online.com/web/p/alumi...31353037333226

The replacement fuse clips I got have a sliiightly different fixing: http://uk.rs-online.com/web/p/fuse-clips/1678351/
but they went in ok; just a little raised from board, as you can see from the picture would be the case.

Haven't managed the other bits yet, need to wait for the soldering iron to cool down so I can switch to a thinner tip.

Also just noticed on the back of the board, where my R3 & 4 are, the board has turned a little black (on both boards). Nowhere else on the board is as dark as these two areas, so I figure I should replace these two as well... will order now.
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Old 08-27-2016, 11:12 AM   #145
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Have C1 & C2 been damaged? On the schematic in the service manual, those would be the two 220nF RF filter caps on the mains input.

Do you at least have a multimeter at hand? You COULD measure those two resistors, y'know... If they're out of spec (+/-5%), then they'd warrant replacing, otherwise replacing them won't really do anything.

Assuming you DO have a multimeter (please say that you do! without lying ), and since the fuse was blown, i'd also check whether the switching FET (Q1) has turned into a wire or not. Drain is the middle leg, and Source is the leg on the right, as viewed from the front of the part.

Last edited by Khron; 08-27-2016 at 11:14 AM..
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Old 08-28-2016, 06:29 AM   #146
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

C1 & 2 were not visibly damaged but I saw a recommendation to change them in a video, so I ordered the parts.

No multimeter. Shall look into getting one.

Fuses weren't actually blown, though one was questionable - but one's fuse clips had definitely broken, and the fuse . Seems as though someone has actually opened it up before me, as there were a couple of screws missing too!

Would I need a multimeter to check Q1? If it's turned into a "wire" that sounds like quite a physical change I should be able to see?


My main query is to do with C35 and C8 being different physical sizes than the originals. Is this normal for electronic parts, for there to be fluctuation in dimension?
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Old 08-28-2016, 09:30 AM   #147
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

A recommendation based on what? Ie. technical motivation, or some logic behind that...

Messing with electronics "blindly" (ie. without any measuring tools) is... well... let's call it "fruitless" in the best of cases; worst case, if you mess with mains-level stuff, you can hurt or even kill yourself.

Well, yes - since none of us have x-ray vision, to see if / how components might've failed internally (in this case, potentially shorted), yeah, you kinda-sorta pretty much DO need a multimeter.

Up to a point, yes, diffent technologies and series of capacitors can / do have different physical sizes, depending on lifetime / ripple current / ESR ratings.
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Old 01-28-2017, 12:02 PM   #148
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all,

So far this thread has been a great help, thanks all!

So, after having not used my M1s for a while I turn them on and one gives out the most awful sound and I immediately turn them off. When I turn them on again there is a bang.
Opening it up its seems C6 had blown, taking with it the trace leading to R3. I removed it along with C7, R3, R4 and C16.
Through this thread I've discovered that my board is likely one of the revisions. The serial in the bottom right corner the PCB ends in F instead of E as shown in the service manual Khon kindly provide (Godsend), C8 and C14 have switched places and there are several other slightly variations which is what my questions are in part about.

First off, the pieces I removed:

C6 is blown and C7 looked cracked, they are also Fuh Yin caps so they will be replaced.
Would these be a good replacement? Or do you have a better suggestion? Anything with a long life maybe?

http://uk.farnell.com/rubycon/200kxw...rad/dp/2342082

When I removed R3 and R4 they tested 37.0k and 37.5k, however the components list in the manual lists them as 47k 2w 5%, but the bands as far as I can make out seem to be orange, yellow, orange, gold. When I check out that colour code though I get 34k, but it does says non-standard. So now I'm really confused? The schematic says 47k but that manual is for the E board not my F revision, and with them both measuring around 37k seems maybe they got bumped down, but with the bands coming out with 34k I'm unsure of what to do here.

C16 I think is fine but since its out I thought I'd just put a new one in but on the component list in the manual it is listed as 0.68uF 100v, on the schematic it says 160v and the actual component on my board says 250v.
So go with what is on the board? Something like this?

http://uk.farnell.com/vishay/bfc2468...rad/dp/1166123

This made me make a list of the differences between the schematic, the component list and my board as well has against my measurements and I found a few other variations. If these components turn out to need replacing, the ambiguity makes me unsure so any suggestions for replacements here
would help.

R5
In the components list is says 10ohm 1/8w 5% and 10ohm on the schematic, but mine has the colours Green, Brown, Gold which I get as 5.1ohm and I get a reading of 5.4ohm.

R20 & R23

The components list and the schematic both say 1.69kohm 1/8w 1%, however the colours are Brown, Violet, Black, Brown, Brown which I can only find as 1.7kohm 1% and the readings are 1.67 and 1.51kohm.

R18

Both list and schematic say 100ohm 1/4w 5% but the colours are Yellow, Violet, Brown, Gold which I get as 470ohm 5%.

R27 & R28
List and schematic claim 100ohms 1w 5% but the bands on mine say 2ohm and my reading on both was 2.4ohm.

C8

List and schematic say 220uF 35v but mine says 330uF 35v

Q3 & Q4
List and schematic claims that Q3 and Q6 are 2n4401. Q6 is but Q3 says 2n5551.
Q4, 5 and 7 are said to be 2n4403 but Q4 is 2n5401

U1
List and schematic say UC3844N but mine says GM3842.

I am a novice, I may be asking some stupid questions so feel free to correct my foolishness.
Any help you could give would be much appreciated.

Also the dreaded C8 is moved on my board but its still a Fuh Yin cap, should I change it out?
C35 is also a Fuh Yin as well as every other electrolytic. Get rid?

If anyone has or knows how I could get hold of a service manual for my revision of the board, if it even exists, It would answer a whole lot of these questions for me.
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Old 01-28-2017, 12:18 PM   #149
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I forgot, some pictures.
Also is that big blob of hot glue they've put all over my diodes gonna be a problem? should I just replace them? I doubt I can get them out of the resin without destroying them. You can see it in the Board picture over Diodes 1-4
Attached Images
File Type: jpg The board.jpg (790.2 KB, 33 views)
File Type: jpg Destroyed traces.jpg (485.5 KB, 23 views)
File Type: jpg R3&R4.jpg (637.7 KB, 24 views)
File Type: jpg C16.jpg (516.3 KB, 20 views)
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Old 02-07-2017, 07:42 AM   #150
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

1) I'm pretty sure the stock C6 / C7 are 10mm-pitch snap-in capacitors. If you go with the Rubycon KXW you linked, you won't be able to sit them flat on the board, and they'll be especially sensitive to vibrations.

2) Since they're quite "roasted", just replace them with a pair of 2-3W 47k's (the actual value isn't that critical, they're only for balancing the voltages acros C6/7, and discharging them after you switch off the power)

3) Yes, that Vishay cap should be fine - or any other PET / PPS 680nF 160-250v cap. That being said, i'm not sure there is (or should be) any reason to suspect the stock one's damaged. If you don't have a capacitance meter, the least you could do is test it with an ohm-meter - if it's not shorted, it's probably fine.

4) R5 is there only as a current limiter - not that big of a different in this case, since the current draw of the PWM chip is only in the order of maybe tens of mA

5) The difference between 1.69k and 1.7k is "academic", and since this isn't (meant to be) a mega-precise circuit, it's quite irrelevant. The slight variation in measured values can be attributed to less-than-perfect probe tip contact, and/or the effect of whatever other components are connected to those resistors (measuring in-circuit will almost always introduce some errors)..

6) The difference could be part of the changes between revisions.

7) See above.

8) See 7). And in this case, a larger value doesn't / can't hurt.

9) No big deal here either, they're functionally equivalent, and the roles they play here don't rely on whatever minor differences there may be between those models.

10) Rebranded / second-source part. 3844 can go up to 100% duty cycle, while the 3842 only goes up to 50% duty cycle. Which is perfectly fine in this case, since the topology's some sort of "emulated" half-bridge or double-forward, and you don't want both FETs to be on at the same time anyway.

11) YES, definitely replace C8 (and all the other crap electrolytics), even if it's not in a hot-spot anymore. As long as you're replacing parts, might as well (try to) make sure you won't need to open them up again anytime soon

12) Nah, those diodes should be fine, they don't need to pass a lot of current anyway. They look like 1A diodes, and since you're drawing (let's exaggerate) 100W from this supply, they'll only need to supply less than 0.5A - multiply that with 0.7v drop across them, that's a measly 350mW.
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Old 02-07-2017, 09:23 PM   #151
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ah Khron, you are an absolute legend, you have helped immensely.
I've picked up a few things since then and understand the circuit slightly better.

I'll pull the parts and do a few more tests before ordering replacements.
I'll post back my findings and how I get on, might be useful for others with the revision board. I also have a capacitance meter now.

Thanks for your help Khron!
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Old 02-24-2017, 08:33 AM   #152
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hello! I have one M1 620 (mk3). He has the same psu like M1 mk2.
First it was the blue led and changed the C8 and all ok.
Now the fuse blow.
I changed like here https://www.youtube.com/watch?v=ThjO7vlb79E&t=1257s
and it`s blow again.
What can i try?
Thanks!
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Old 02-24-2017, 11:17 AM   #153
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I'm not sure if anyone mentioned this already, but everyone should start by trying to scrape off that cream white / yellowish stuff ...

That was supposed to be a somewhat elastic material holding the bigger components to the board and prevent vibrations and otherwise be an insulator... but as it dries out and turns out that yellowish color, it can become slightly conductive and cause shorts under that substance.

So I would first try to scrape off that substance and then clean the pcb with a bit of isopropyl alcohol.

Last edited by mariushm; 02-24-2017 at 11:19 AM..
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Old 02-25-2017, 04:00 AM   #154
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Any ideea?
The PCB it`s clean.
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Old 02-25-2017, 05:07 AM   #155
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Someone please mesure between the legs of the C33?
I have one working and in that between the legs of the C33 seems to be in short. But it`s the good one.
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Old 02-25-2017, 07:55 AM   #156
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

A life-lesson: never, and i mean NEVER replace a fuse after it blew, BEFORE determining why it blew in the first place. Otherwise you're just risking causing even further damage when you try to power the unit up again.

Is the C33 the same as in the schematic in the service manual, ie. 0.1uF between the secondary ground and the chassis eath? And are you measuring the good one with the cable to the audio board connected, or not?
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Old 02-25-2017, 08:40 AM   #157
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Aftre i watch that video and change all the parts like there i put the fuse back. This was the only way to know if it`s work, no?
And both had the cable connected to the audio board.
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Old 02-25-2017, 09:02 AM   #158
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well, that's the problem with following "recipes" without actual testing / reasoning

You haven't confirmed whether it's the same C33 though.
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Old 02-25-2017, 09:11 AM   #159
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yes, it`s 0.1uf like in schematics (i will take out C33 and hope to find my esr).
I mesured C27 and the same. Short.
On the good one it`s short between C34 (ground) and C39, C38.
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Old 02-25-2017, 09:18 AM   #160
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Default Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hmm... You have a multimeter, right?

Disconnect the cable between the power supply and the amp board, set the meter to diode test, and measure each of the rectifier diodes on the secondary (D10, D11, D12 and D13).

PS: You should be able to find the service manual among the first pages of this thread. The power supply schematic is on page 14. Refer to that, when you name the part names (not necessarily what you can read on the board itself), just so we're on the same page.

Ah, i found the caps you mention. C34, at least in the schematic, seems to have its legs tied together(?). C38 and C39 are the snubbers on the two secondaries. If you look at the schematic, "of course" it would appear that one end of each would be "shorted" to ground - there's only half of each secondary (a few cm of wire) between that end and the ground

Not everything is what it might seem at first...

Last edited by Khron; 02-25-2017 at 09:21 AM..
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