Repairing Alesis M1 Active mk2 Monitor Speakers

For Friday’s show, we used Alesis monitor speakers that we had in the lab, plus Steve, one of the students, supplied two.

Alesis M1 Active mk2 speakers

During installation, one of the speakers started winking its blue power light and ceased playing sound, and before the show another did as well. Steve found a Studio Central forum post suggesting that the problem was due to a failed electrolytic capacitor that gets baked by a hot resistor right next to it, and a quick peek inside confirmed that it was a likely explanation and fix.

Alesis M1 Active mk2 speaker, circuit boards and interior

After unscrewing, the back panel lifts out and reveals the power supply board mounted vertically on a metal shield, and the crossover/amplifier board mounted flat on the panel.

Alesis M1 Active mk2 speaker power supply board

The naughty capacitor, C8 (actually its replacement after I finished), is in the center red rectangle next to the offending resistor. Another bad electrolytic capacitor whose number I forgot to catch is featured near the top of the board. Both of these tested bad with my Capacitor Wizard in-circuit equivalent series resistance (ESR) tester; all of the other electrolytics on the board tested good.

It was simple work to remove and replace the two capacitors on each board, and it brought both speakers back to life. Thank you, forum posts and Capacitor Wizard!

BTW, are electrolytics supposed to look like this?

Leaky electrolytic capacitor

Two caveats about this repair. First, I should have used 105°C capacitors, but I could only find 85°C caps on short notice, so these will fail quickly and need to be replaced again. At least now it’s known exactly what needs to be done. And second, the forum post suggests moving either the resistor or capacitor to get them further apart, which is a great idea but which I haven’t done yet. I’ve been trying to think up a clever way to stick a little heatsink on a vertically-mounted resistor, which might be a better solution yet.

409 Responses to “Repairing Alesis M1 Active mk2 Monitor Speakers”

  1. Kenneth Rosén says:

    Thanks again Mike
    It is a good approach. I will “go for it”
    About the “basic skills in soldering/desoldering and of course the right equipment”.
    I´m a welder, have to take it easy:-)
    It´s funny with small things too.

    Kenneth Rosén
    Sweden

  2. MikeB says:

    Kenneth R

    Well, the poweramp is not welded but it sticks to the circuitboard as if it was bolted on. Be sure not to damage the pads when removing the shit…

    and ….

    Lycka till

  3. Kenneth Rosén says:

    MikeB and the Forum is the best thing just now! (You speak Swedish good Mike):-) Lycka till.
    I did it. I changed the poweramps for the woofer and the speaker is in function now.
    Alesis Support in England told me, the best thing you can do… “buy new ones”… speaker is expendable
    Thanks Alesis!!

    And thank you very much for this blog Keith
    Kenneth Rosén

  4. Perfeito!
    Minhas Alesis apresentavam o problema do led piscando há bastante tempo, mas sempre eu resolvia desligando e religando a caixa alguns minutos depois. Até que chegou o dia que isso não resolveu mais e tive que procurar a solução. Encontrei a solução aqui! Eu substituí o C8 (220uF/50V 105ºC), R3 e R4 (47K/3W). Mas mantive longos os terminais dos resistores para ajudar a dissipar o calor e o capacitor foi soldado distante da placa com o mesmo objetivo. Depois de duas semanas os monitores continuam funcionando perfeitamente! Obrigado pelas dicas! ;-)

  5. RickC says:

    Excellent work!!!
    Never really done anything like this before , didnt even have a soldering iron, so was proper buzzin when i managed to fix my monitor in an hour (checked and double checked everything) and for only $20 nz
    so saved myself a packet!!!
    And for anybody who thinks this is going to be too difficult, give it a go!!
    Thanks again

  6. Pappy mcfae says:

    Found out my problem was a bad solder joint between L1 and it’s hole. I restripped the wire, tinned it, then soldered it in nice and tight. I didn’t get my power supply schematic, but I got a parts list. Woohoo!!!

  7. staffan says:

    hey,

    i have another problem with my monitors, yesterday the left tweeter just died on me. it came from nowhere, no glitches or anything, it just died.
    i´ve scouted out a store that can order replacement parts for me.
    would it be wise to have a look at the circuitboard as well?
    i thought since it just died so suddenly maybe a capacitator was blown or something.

    thanks!

  8. Sam Ash says:

    I had the same problem (left channel M1 Active first pulsing, then totally dead), and replacing C8 fixed it. Thanks to Keith and Studio Central for posting the fix!

    I slipped insulating sleeving on the replacement C8′s leads, and soldered the cap about an inch above the board rather than pushed down flush to the surface. I was able to bend the cap leads so that the capacitor body is located between the connector for the on-off power switch and the corner of the metal heatsink; this moves the capacitor an inch or so from the excessively hot power resistor near it on the board. Hopefully this will extend the life of the replacement cap.

    If you try this, don’t forget to slip insulating sleeving over the cap leads, otherwise they may short to each other or to the metal heatsink nearby.

    -Sam Ash

  9. Camera Obscuro says:

    On the power amps in the M1 Active – each amp board contains two power amps, one for the tweeter and one for the woofer. There are also a few (low power) op-amps which are part of the active crossover network, and also apply a little bass equalization to the woofer to extend its range a tiny bit.

    Each power amp is based around a single National Semiconductor integrated circuit – I think it’s the LM 3875 or LM 1875, though I don’t recall for sure. Probably the tweeter uses the lower powered LM 1875 while the woofer uses the higher power LM 3875.

    You should be able to read the part number off the IC – you’re looking for the two relatively large IC’s on the amplifier circuit board that’s bolted to the metal heatsink. These integrated circuits are relatively inexpensive, so if the power supply is known good and the speaker doesn’t work, it’s worth simply soldering in a replacement IC to see if that fixes it.

    Knowing the overall signal flow in the speaker enclosure can help diagnose symptoms. If the power supply is known to be good (by swapping to the other speaker), and either the woofer or tweeter produces no output, almost certainly the corresponding power amp IC is dead. So that’s the one to replace. (It is possible for low power op-amps to die, but it happens very rarely – high power IC’s die much more frequently, so that’s where I’d start.)

    Copper desoldering braid is probably the best way to desolder one of these power amp IC’s. First unbolt the IC from the heatsink, then use the braid to remove as much solder as you can, then heat the pads and wiggle the IC gently until it’s out.

    I suggest replacing the thermal washer or heat sink thermal compound between the IC and heatsink when you install the new replacement IC. Otherwise it won’t live long.

    -Obscuro

  10. Camera Obscuro says:

    staffan says:

    yesterday the left tweeter just died on me. it came from nowhere, no glitches or anything, it just died.

    ============================
    Staffan – it could be the actual tweeter itself, or it could be the power amp driving the tweeter that died. There are other possibilities, but these two are probably the most likely.

    Before you go buying new parts, it would be good to know which component has failed. One of the best tests you can do is to swap the entire back panel, complete with both circuit boards, from your good M1 Active to the bad one.

    After doing the swap, if you have the same symptom – no sound from the tweeter – then almost certainly the tweeter itself is dead. But if the tweeter comes back to life when you swap the board, it’s probably the power amp driving the tweeter that’s dead. In that case you most likely will fix it by replacing the corresponding IC (integrated circuit).

    -Obscuro

  11. Zachary says:

    Hello!

    Are the M1 Active and MKII tweeters interchangeable?

    All my best,
    zachary

  12. Spencer says:

    Great blog! I am so glad to have found this.

    I have the same models of Alesis active monitors and within a few weeks of each other, both my woofers have stopped responding. The blue LED is solid and both tweeters work fine.

    The surrounds and the cones both look fine and I notice when I gently push the cone back into the unit it starts to engage and make noise. I imagine something has come unglued.

    Is this something I can fix myself?

    Any advice is appreciated!

    Thanks,.

  13. Alan says:

    Spencer

    The scratching that you are hearing probably means that you “fried” the voice coils. Check the resistance across the speaker terminals. You should see 4 to10 ohms or so if the voice coils are OK. If they show no resistance the speakers are shot and need to be replaced.

  14. Pappy mcfae says:

    Your only hope is if the special wires that go from the yoke of the speaker to the back of the cone are the issue. If it’s just a question of a lose connection near the yoke, that’s easy to solder. If it’s a problem in the voice coil itself, then the speaker is more or less shot.

    You might be able to get the speakers re-coned if there is a specialty shop in your area that does this. Either that, or you can go to Alesis’ home site and order the drivers. I think they’re in the neighborhood of sixty bucks a piece.

    Cheers,
    Pappy

  15. Alan says:

    For Zachary

    I don’t know the specs on these tweeters but most are pretty much in the same frequency range. The only difference may be in power rating. If they fit into the mounting hole I’d try the substitution. You certainly won’t damage anything.

  16. Keaver says:

    Hello. thanks for this blog, its been helpful – I managed to fix one of my broken M1′s which had completely died by replacing the capacitor, and I’d been having problems with the other which i was still using (flickering led, sometimes wouldn’t turn on) so i figured I’d replace the cap in that one too.
    No flickering led anymore, and powers up every time, but no tweeter output. I don’t understand why the tweeter would suddenly stop working? Any ideas?

  17. Alan says:

    Keaver-

    you might recheck to see that you plugged the tweeter connector in properly and that the wires are intact. (sometimes they can break during handling). If they seem OK try swapping the power amp from the other speaker, as mentioned in previous posts, to see if the power amp is the problem.

  18. Obscuro says:

    Zachary says:

    Are the M1 Active and MKII tweeters interchangeable?
    =======================================
    Zachary, you’re in luck: they are the same tweeter. At least, they WERE the same tweeter eleven years ago when I worked for Alesis, back in 2009.

    Note that the old 1st gen Monitor One’s had very different tweeters. You can tell them apart because the old tweeters had a grey-blue faceplate, while the later ones in the M1 Active and Mk II are charcoal grey (no blue any more).

    Alan – you’re right that you usually won’t hurt a tweeter by swapping one for another. But believe me, all tweeters are not alike. The sensitivity, resonance frequency, dispersion pattern, and electrical impedance all vary widely from one to the next. If you swap in a different tweeter, therefore, you usually completely bugger up the smooth frequency response designed into the speaker system – the crossover will no longer work as designed, and the new tweeter will usually be either “hotter” than the old one, leaving you with sizzling treble, or “colder” than the original, leaving you with a dull speaker that sounds as though you’re listening to it through a pillow.

    The crossover network is the hardest thing to get right in any speaker system, and it is hardest of all in a passive loudspeaker such as the Monitor One and Monitor One Mk II. Swapping a different tweeter into one of these will completely destroy the carefully designed flat response and smooth crossover from woofer to tweeter. In a nutshell, if you care about sound quality, NEVER swap one model of tweeter for another unless you intend to also completely redesign the crossover network, and have the very expensive design, test and measurement tools needed to do the job properly (the Alesis speaker design crew used a $5000 B&K measurement microphone, for instance!).

    -Obscuro

  19. Lars Jensen says:

    Here’a a new twist to the same old problem we all have, aka my story:

    A while back during this extremely cold winter one of my MKIIs started flickering on and off, the woofer going “blop blop blop” together with the LED turning on and off. I googled it and found this thread, but before replacing any components I wanted to make sure it was the powersupply that was the culprit. I took the powersupply from the working monitor and put it in the non-working one, and there was no change, the problem persisted. I then figured it was the poweramplifier, so I ordered a new one and installed it. Nope, same issue.

    I gave up on the monitor and got myself a new pair instead. I like (and am accustomed to) the sound of them so much that I didn’t want to go any other route.

    However, today I wanted to try a few more variations of swapping units from one monitor to the other from the pair no longer in use. I first took the powersupply from the non-working monitor and put it in the working one, and it powered up and worked fine. Then I did something I shouldn’t have done, I put the working powersupply in the non-working monitor and switched on…a short cracking sound was heard before the LED started flickering as the woofer went “blop blop blop”. I didn’t think it was a problem before I put the powersupply back in the originally-working monitor, now BOTH of them flicker and go “blop blop blop”!

    Any ideas why this might be? I’m positive I didn’t mix up the boards, and as mentioned I have fresh poweramps, and I can’t see that any components look burnt. I’ve pretty much given up on them now as I have another pair that I enjoy working with, but it would be nice to have a second pair as backups or to just simply use in the living room with some EQ to accommodate for comfortable everyday listening.

  20. Dimitre says:

    I’ve just bought C8 & R4 replacements and noticed maybe C38 is burnt, maybe R27 too.
    Did you already replaced that ones and it worked fine?
    in this case what are their values?
    Thanks

  21. Thomas says:

    @Lars
    I have the same problem with one of my 2 Speakers. Sometimes it work fine, then it starts randomly like pumping and cracking… like the protection-circuit goes active… sometimes it turns off (blue light goes out) after 2-3 times and turn back on after some seconds… i resoldered the complete 2 boards and checked the caps… the funny thing is, if i finished work and mount the unit together, it works sometimes about 10-20 minutes… after running it under full load, the problem turns back…but not always with the turning out light… its very strange.. my next idea would be to replace the power amp IC… there is nothing written on it… where you get them ?

  22. Lars Jensen says:

    @Thomas

    A lot of odd issues with these monitors it seems. Too bad, when they sound that good. Mine never turns on anymore though, they just flicker on and off constantly.

    I got the replacement board for it from this site:
    http://www.instrumentalparts.com/alm1acmkm1mk.html

  23. Edd says:

    Hi there this is a great thread!

    I’ve bought these monitors(S/H) and have encountered some issues.

    1. One LED is much brighter than the other yet there is no noticeable difference in sound quality/volume.

    2.One of the bass drivers at a higher volumes ‘fuzzes’ particularly >150Hz. Its almost as if its resonating with itself, could this be a blown driver: but the sound with a HP filter/Lower amplitude is still great? So i was thinking it could be something else, any suggestions?

    Thanks Guys.

  24. Thomas says:

    @lars and edd
    Do you checked the voltages from the powersupply ? Should be around 30v.

    ok, i found the fault on my speaker. The problem is, in cause of the vibrations the layerconnections from the powersupply are bad. Its anyway a bad choice to make multilayer pcbs in highpower parts… Just resolder the little layerconnections around c8 with much heat and much tin. I also replaced the IC there, but i think this is not necessary.

  25. cory says:

    “I’ve just bought C8 & R4 replacements and noticed maybe C38 is burnt, maybe R27 too.
    Did you already replaced that ones and it worked fine?
    in this case what are their values?
    Thanks”

    Anyone know the value of the c38 and r27 or where i could find them? Mine are crispy too. The C8 and R4 actually look fine, but plan on replacing anyway. I don’t know where to find a circuit diagram of the product.

  26. Francisco M. S. says:

    Hello!
    Someone will help me?
    My Alessis M1 Active 620, this noise with a very strong speaker, does not mitigate the pot, does not alter the volume, even without any audio cable conectado.Ja switched capacitor C8, based on surveys of other users, but I got no result. When I press the power button, the blue LED lights, and then lights the red, producing noise (snoring) very strong.
    The board seems perfect source, +36 v,-36v, —-, +18 v and-18v
    I have the three years, and never had problems with the equipment.
    Thank you, who can help me!
    Francisco M. S.
    Florianopolis – Brazil
    * Sorry typing error, I use Google tradudor.
    xikosanto@gmail.com

  27. Jon Doe says:

    Thank you, Thank you, Thank you!!

    Both monitors had the blinking blue light/clicking issue and were easily fixed switching out JUST the C8 caps in each with replacements from digikey. I have some limited experience with soldering (but never to a circuit board) so a friend helped me out while I observed. Really easy, I could have changed them out.

    I have been without a working pair for a while, such a great feeling when they both powered back up again with no issues. The are very solid monitors, GREAT to have them back.

  28. jack says:

    ty guys 4 sharing this problem it works again ,by changing the those 2 capacitors ,from the picture ,xd ty

  29. nahum hernandez says:

    i need to fix my speaker monitor, it seems like the speaker is broken,it sounds, but distortions the sound?

  30. james says:

    Hi,

    Did anyone find out what the value/spec of the RT1 component is?

    thx

  31. Pappy mcfae says:

    RT1= THERMISTOR 10 OHM 2A NTC

    Cheers,
    Pappy

  32. Pappy mcfae says:

    Alesis part number 0-22-0100

  33. james says:

    @ Pappy mcfae

    thank you!

    think i found the right one here:
    http://uk.farnell.com/epcos/b57153s100m/thermistor-ntc-10r-2a/dp/1688795

  34. Pappy mcfae says:

    Yeppers, that looks like the right one.

    Cheers

  35. Steve says:

    Re Alesis M1 Active MK2 speakers – on one of them I have the flashing blue light, and the speaker does not produce sound. Any idea exactly what kind of capacitors to buy? Thanks!

  36. amrk says:

    This is the same problem with the Alesis 520s and 620s

    In order to free up heat issues with that capacitor, simply solder it to the other side of the board if it will fit. No hot resistor on that side :) On my 620, all that is on that side is insulation anyway, but it would be good to keep the capacitor’s profile down when do it this way so it doesn’t snag anything. I used an electrolytic 220uF 35V 85 deg for C8 and it works just fine….for now.

    Such an easy fix! Thanks!!!!!

  37. adriano says:

    Hello. I have a pair of Alesis M1 Active mk2 as well. Unfortunately the right speaker after some time (minutes) after power up starts to crackle and after a couple of minutes it goes completely silent. My guess is the voltage of the power unit kneeling down (I have a degree in electronics albeit i am not experienced in repairs nor I have workshop tools except for a multimeter and a soldering iron). Has anyone experienced the same problem?

  38. kettle says:

    hi guys,
    so it happened finally to me too. Actually the head into my right monitor.
    Fuse ok. C8 looks like a damn ugly bbq.

    Just found this on ebay:
    http://cgi.ebay.de/Kondensator-Elko-330-f-35V-10-Stck-/160342627024?cmd=ViewItem&pt=Bauteile&hash=item25552a52d0 seems the exact copy but still max 85°c

    Also this, up to 105°c , BUT 200V instead of 35V. Does it make a big bad difference? (im quite a noob in electronics)
    http://cgi.ebay.de/10-x-Capacitor-Elko-330-F-200-V-105-C-NEW-TOP-/120606129024?cmd=ViewItem&pt=Bauteile&hash=item1c14af7b80

    thx for the help!
    matt

  39. kettle says:

    So guys. It works!
    Took me less than one hour.

    That Kondensator Elko 330 µf 35V found on ebay is quite good. Smaller than the original so you can fix it up to that hot R4. Hope it will work for a long time, even on 85°C base

    THANK YOU!

  40. Ponti says:

    Hi,

    my ALESIS MK2 is also broken. Do you have a schematic?
    Think in my case it’s not the capasitor, when switching the MK2 on, it made a little
    “bang” ant the fuse of the house broke. I opened the speaker, the fuse also was broken. Think there is something going wrong, but i need a schematic.

    Greetings from germany
    Ponti

  41. Keith Neufeld says:

    Ponti, I’m sorry, but I haven’t reverse-engineered a schematic yet.

  42. BlueBlink says:

    Hi,

    JunFu caps are known to be ‘bad caps’ so this is NOT any kind of a mystery, ALESIS or who ever they hired to build the PSU board should have known better.

    http://www.BADCAPS.net/forum/printthread.php?t=388&page=2&pp=40

    I Also have a question.

    Are C8 and other capacitors Polarised or Non-Polarised?

    Because I don’t want to get the wrong ones. It seems there is a big difference between the two kinds, and I wouldn’t want to see people causing more problems trying to fix things.

    http://www.edaboard.com/thread56473.html

    My (C8) is a JunFu 220µf 35 V 105º green coloured cap, also used for the 4 caps to the left of the transformer on the PSU board.

    From reading the included link (see above), I guess the originals are Non-Polarised, can anyone please confirm this for me before I source some new radial electrolyte caps with the correct characteristics.

    Thanks,

    Blink.

  43. Pappy mcfae says:

    I don’t know where you’re getting that from. The caps that need replacing are clearly marked as polarized, both on the cap and on the board.

  44. Patrick says:

    Thanks for this useful page :)

    I tried repairing my circuit after one of the speakers died one day. I wasn’t there when it died – I just came home after leaving them on and one had would no longer work.

    I replaced the fuse, and sparks flew when I turned it back on! I replaced RT1, and using the meter which I purchased for this fix, I couldn’t get a sensible reading from C8, so I tried to replace it …. it went horribly wrong and I ended up damaging the connections to both pins of C8 on both sides of the board… I horribly bodged it together and I think C8 is more or less in place…

    Now the old c8 is out, I tested it and it seems to be fine :( :( :( :( :(

    So R15 looks damaged. I’ll replace that and if that doesn’ solve it then I’m going to have to buy a replacement board.

    So it’s 0.22 ohm. What power rating is it?

    Any help appreciated ….

  45. ontologist says:

    I appreciate your words here, this worked for me! $1.50 at Radio Shack beats a $100 repair fee any day! Same symptoms, light was flashing, replaced C8 only, works like new! 5 stars A plus!

  46. Marvel says:

    Please help! The same thing described here happened to me, I opened it, first thought it might be the fuse, but it’s also the C8 capacitator. I’m trying to fix it myself, but I can’t remove the board even though I removed all 4 screws which were located in the corner edges. Please help and let me know if the plug box is anyhow connected with the board because it’s loose in all parts except under the plug box, but since there were no screws left, I thought that it might be fixed with glue, soldering iron or something else and I’m afraid to use the force and just pull it out. Please help, thanks!

  47. kettle says:

    Marvel > 2 screw under the glue

  48. Alan says:

    To Patrick…
    R15 appears to be a .22 ohm 1/2 watt +/- 5% tolerance resistor in my unit. Pay attention to the tolerance (Gold 4th Band) when you shop.

  49. Marvel says:

    Haaa! Thank you!:)

  50. Marvel says:

    I replaced the C8 and thought that it’s gonna work, but I plugged the cable in, turned the switch and nothing happened. What a disappointment, seems I’m gonna have to go and take it to service.:(

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