Alesis M1 Active mk2 Biamp Monitors

[technician]

The flashing blue LED and loss of sound on the Alesis M1 powered monitor is caused by failure of capacitor C8 (220uF, 35V) on the power supply board. It dries up due to its proximity to resistor R4 (47K, 2 W) which gets very hot. This is a design fault.

Remove the power supply board (4 corner screws and 2 mains connector screws) and disconnect the two plugs. Carefully desolder C8 and replace it. Its value is not critical (220 to 470 uF will do) but it should be a 105 deg. type, preferably at 50V.

Remove R4 and replace it with a similar resistor with its leads bent so that it is nowhere near C8, otherwise the fault will return. One end may be connected to one of the existing R4 solder pads (furthest from rear of board), and the other to the top end of resistor R3. Check that you have connected it correctly by inspecting the PCB tracks.

Replace the board and all screws and plugs before testing.

[Tweak]

Looks like we have a technician in our midsts. Welcome!

[Rimskidog]

Unfortunately pschmailinglist appears to have last posted 9 months ago. I hope he wasn't holding hsi breath!

[loopfish]

im about to test technician's guide to repairing faulty M1's...

this is my 2nd M1 that has blown now....

the first blue after suffering from a pulsing blue LED....this 2nd monitor has simply stopped functioning - no sound or LED activity. I have narrowed the problem down to the PSU, as the x-over unit still works fine (as tested inside other monitor)

I really love my M1's, but its pissing me off that they keep dying!

[loopfish]

The flashing blue LED and loss of sound on the Alesis M1 powered monitor is caused by failure of capacitor C8 (220uF, 35V) on the power supply board. It dries up due to its proximity to resistor R4 (47K, 2 W) which gets very hot. This is a design fault.

Remove the power supply board (4 corner screws and 2 mains connector screws) and disconnect the two plugs. Carefully desolder C8 and replace it. Its value is not critical (220 to 470 uF will do) but it should be a 105 deg. type, preferably at 50V.

Remove R4 and replace it with a similar resistor with its leads bent so that it is nowhere near C8, otherwise the fault will return. One end may be connected to one of the existing R4 solder pads (furthest from rear of board), and the other to the top end of resistor R3. Check that you have connected it correctly by inspecting the PCB tracks.

Replace the board and all screws and plugs before testing.

OK, I have managed to try this fix on my Alesis, and it works!! Thank you very much, mr technician! You saved me LOTS in Numark's service fees

[~X~]

I changed my capacitors and still nothing. The dreaded blinking light thing continues.

I have to say Im a little disappointed with Alesis. I even bought an extended warranty for my monitors. Yes, my warranty was out by about a month when I contacted them wanting my power supplys replaced. They werent willing to work with me on this KNOWN problem.


So heres my question:
I replaced my capacitors with 220uf, 35wvdc, 85*. Could this be the problem? I know another voltage and temp rating was recommended but this is all I could find locally. Are there other parts of my power supply that may be easy for me to diagnose and fix? (Im not really an electronics repair guy but the capacitors were easy)


Any help on this will be greatly appreciated. Thanks ~X~

[loopfish]

do u have a multimeter? would it be possible for you to test the resistance of R4? I managed to kill one of my R4's when I was trying to fix the capacitor...

also, i'm assuming the little clear fuse by the mains socket isnt blown?

do u know for certain that it IS the power supply section that is faulty? have both of your monitors blown? if not, u can swap out the PSU section from your working speaker just to make sure it is definately the PSU which is faulty in the other monitor...

the voltage rating of the capacitor just determines what voltage it can handle before it overspills/arcs/overheats, losing its smoothing/AC hum removal properties... I'm wondering if the factory 35v choice is not tolerant enough for its purpose, and thats why Technician recommended 50v... I used 440uF, 50v, 105d electrolytics, and they work fine...
for the sake of a £0.23 component, its worth trying another one - plenty are available online..

does your local electronics store have a decent multimeter with which they could possibly test your capacitors? (capacitance tests are only available on the more expensive meters) My local Maplin store did have one, and were friendly enough to test my capacitor to make sure it was functioning correctly.

The pulsing LED behaviour really is indicative of what would be caused by the removal/malfunction of a voltage-smoothing capacitor, in a power supply circuit...

one last thought - are you a fairly competant solderer? it seemed to me quite easy to accidentally lift up/break the track pad (which the legs of the capacitor are actually soldered to), if not quite careful....

[~X~]

Thanks
No, I havent checked my R4. Good advise though and I will check it. My fuse is good Im sure of that.

As far as my soldering goes I think Im pretty competent, it looks good. I will seek out the 50V capacitors and use them and replace both R4's while Im at it.

Thanks again to everyone who responded. Sorry for not checking back sooner to keep you posted. ~X~

[wartex37]

Hello.

Where to buy this Capacitor C8??? I have the same problem with mine monitor and i live in Denmark. Dont think i can by this one in my country?

Thanks in advance.

[gareth3266]

Hmmmm. I changed my capacitor and now my fuse keeps blowing!

I've multimetered most of the components and they seem fine. I've replaced the capacitor like for like (a 220uF, 35V, 105 deg) but every time I change the fuse and flick the power switch the fuse pops.

Would it do this if I'd been unlucky and got a duff replacement capacitor?

[holderofthehorns]

Excellent thread.
I do have one which has died in this fashion.
Like the M1 Actives so much, I Ebay'd 2 more.

After this fix, I will have enough of them to do surround!

[sickfreak]

Hi Guys,

I'm not particularly well up on technical stuff but I own a set of Alesis M1 Active MK2s. I was using Ableton recently and three channels "broke" emitting a really high pitched squeal and maxing out their respective volumes. My left speaker made a popping noise before I could exit the programme and now it won't turn on.

Am I right in assuming this is a fuse blown? I tried swapping my plugs around and that one speaker won't turn on anymore. No blue light.

I am hoping to put in a new fuse, is this easy? I can't solder, but I was hoping to just open the back and add it in. A friend says this is easy. What fuse do I need to buy? Anyone have any experience of this?

Apologies for the retarded questions, just as I say, I am not sure of this stuff.

Thanks...

[gareth3266]

Hi,

The fuse is dead easy to replace and is just in a fuse holder which you snap the replacement into - no soldering required!

The fuse you need is a 5A 250V, miniature.

Mine are still dead - can't locate the new problem that started after I'd replaced C8. I use Dynaudio BM-5A's but had kept the M1's as a comparison so they're not stopping me working, but it's annoying not to have them in use!

[think_cliff]

hi there, i was wandering if anyone could enlighten me of my m1 mk2 issues. i believe i have identified the issue as a problem in the low frequency driver, to put it simply, it has cut out. the most perculiar thing is that if i gently touch either side of the cone it will jump back in, therefore i concluded that it couldnt be any crossover problems and i assume (as it jumps back in with its regular reproduction) it is NOT an amplification problem. would i be right to believe that i have a faulty/damaged driver? i was hoping it would be something simple like a loose connection so i promptly removed the offending cone and examined. To my suprise everything seemed to be intact with reasonable connections although there was a small object that fell out, it seemed to be a tiny bit of insulation possibly from a cable or coil (when i mean tiny i mean 2mm black/turqoise). i then accidently dropped it n my furry carpet (woops!!) so i couldnt clearly identify it. i am baffled, i believe i understand the workings of a driver to be the almost the opposite of a dynamic microphone? correct? the question is will a new driver (if available?) solve my problems? kind regards, Cliff.

[toddhorton]

Same problem as everyone else... but replaced C8 AND both R4 and R3 resistors. Whereas before the problem was just a flashing blue light and no sound, now nothing at all after closing up and powering on. Opened again and the fuse does not LOOK blown. However, the C6 capacitor looks as though it either has leakage on it from the originally blown C8, OR possibly it is blown too? Is that known to happen?

Another question: Could I not be getting any power at all if the replaced C8 and R4, R3 resistors were somehow not soldered perfectly. I mean, I'm not too bad at soldering but it's tricky getting it right, sometimes. Like maybe a track pad came up a little or overheating while trying to get the bead around the base of the lead right etc.

Is there a simple way to test which component may be the culprit by using something from the other working monitor since I don't have a meter to test caps etc.? Desolder C6 from the other monitor and try it in the broken one? Anything else that won't be too crazy and cause me to wreck the other monitor too?

Thanks for any help. I'm desperate to get back to a paid mix job...

[Folklore]

Well, now this has happened to one of my M1s as well. However, I had a look at the PSU card and C8 is not burnt. I therefore put the "healthy" PSU from the monitor that still works into the one that does not to see if the problem perhaps lies elsewhere. And Heavens to Murgatroid, it still pulses on and off, and at the same time the woofer moves in and out.

Any idea where the culprit might be then? I'm not really keen on the idea of buying a completely new crossover or something like that if it can be fixed easily (and cheaply) just by replacing some components.