Repairing Alesis M1 Active mk2 Monitor Speakers

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I know this might make me sound like a "vulture" / "scavenger", but with filth's frustration with this project, i struck a deal with him and bought his dead pair of M1's

First one was delivered last week, its pair is due next week.

This first one turned out to have quite the "chain" of problems. Before even plugging it in the first time, i took the liberty of doing the relocating trick with C8, as well as replacing D5 with a 1A fast-recovery diode. All the silicon on the primary measured fine. Amp-board-less testing revealed that the PWM controller was powering just fine, but both outputs were at least 50% higher than they were supposed to be (+/-36v and +/-57v instead of +/-18v and +/-36v).

After a quick consult with Th3_uN1Qu3, i even swapped out the TL431, to no avail. Which then led me to start measuring the resistors around it, and R30 (100k) turned out to be the culprit - open-circuit. Replacing it brought the output voltages back in line

The overvoltage, though, had killed the LM3886 woofer amp (both output transistors shorted through, so V+hi, V-hi and the woofer output were basically fused together). Fortunately i still had a few sample ones from well over a decade ago, and once that was replaced as well (complete with cleaning the heatsink, the mica isolators and the LM2876 tweeter amp, and adding some fresh Arctic Cooling MX-4 paste), the thing was completely revived

Looking forward to receiving its pair now...

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Nice work, Khron!

Yeah, sometimes finding that one lone failed part that you least expect to be failed can be quite a challenge (and I will admit that I get stuck once in a while too.) So like I mentioned, when doing component measurement in circuit and nothing appears to be too far from what it should be, it's time to start removing parts and checking things out of circuit. On a board with lots of tiny SMD parts, I can understand, of course, why one might hesitate to do that. But this PSU board seems to use only through-hole parts, which IMO is a shrinking convenience when it comes to troubleshooting in this day and age of SMD-everything.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Thanks, but I couldn't have done it (or had the motivation to take the dive) without all you good people here "Even" Th3_uN1Qu3 i met through here, many years ago

Either way, the pair of the above-mentioned first monitor arrived at the post office today, I'll have to see whether I can get a car ride from a friend today or tomorrow - lugging a 10kg box for 2km on foot isn't all that tempting (20lb / a mile and a half)

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

"To whom it may concern", just finished the somewhat more detailed write-up (with photos) of the repair mentioned a couple posts above

https://khronscave.blogspot.com/2021...ilitation.html

The second one though...

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

"To whom it may concern", just finished the somewhat more detailed write-up (with photos) of the repair mentioned a couple posts above

https://khronscave.blogspot.com/2021...ilitation.html

The second one though...

Welp. I've been meaning to read through that for a good few days now, but just kept delaying and wasting time with other things. Finally checked it out today... and again, nice work, there! I really like the attention to detail you give to these speakers, and I'm sure they are likely to last a very long time with these repairs/modifications.

Let us know when you get to the 2nd set. Curious to see what that one was like for you to be shaking your head like that.

"Even" Th3_uN1Qu3 i met through here, many years ago

I see he posted a comment on your thread there, but I haven't seen him post here for a good while now. If you keep in contact with him (or at least on a fairly regular basis), say cheers from me. I always enjoyed reading through his PSU posts, and still do once in a while when I encounter a stubborn PSU and need ideas what to look out for if most of the components check out already.

lugging a 10kg box for 2km on foot isn't all that tempting (20lb / a mile and a half)

LOL, I like how you provided the conversion above for us non-metric Yankees.
Luckily, I was born overseas (Europe) and lived there as a kid, so I know both metric and US/imperial/"standard" systems.

Also, I've been there and done that what you said above... well, not for 2 KM - more like 1-1.5 KM (~0.8 mi). It was with two APC BackUPS CS 500 VA units (IIRC) with the batteries still inside. They didn't use the "small" batteries, but the slightly larger ones (not sure what the case sizes of these are called.) This was a few years back at a university I attended. Basically, I found these UPSes next to an industrial dumpster behind one of the buildings. Found a "service tech" guy dumping more electronics stuff in that dumpster and asked if I could take the UPSes, which he was OK with. So I put one in my backpack (good thing I wasn't carrying any of my textbooks and only a notebook with some pencils) and the other in my hands. I think each unit weights about 6-7 Kg (so about 12-14-ish Kg total)... and I lugged those around to another class before heading back home/my college rental apt. So yeah... after carrying those things home, I felt my hands were somehow longer after that.

Oh, and the following day, I found an old, broken-apart HP 6291A lab power supply. That one was also quite heavy with its big hunkin' transformer inside. It didn't fit in my backpack, so I carried that one in hands as well.

Oh, the things I've done for picking up scrap electronics!

[goodpsusearch]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Also, I've been there and done that what you said above... well, not for 2 KM - more like 1-1.5 KM (~0.8 mi). It was with two APC BackUPS CS 500 VA units (IIRC) with the batteries still inside. They didn't use the "small" batteries, but the slightly larger ones (not sure what the case sizes of these are called.) This was a few years back at a university I attended. Basically, I found these UPSes next to an industrial dumpster behind one of the buildings. Found a "service tech" guy dumping more electronics stuff in that dumpster and asked if I could take the UPSes, which he was OK with. So I put one in my backpack (good thing I wasn't carrying any of my textbooks and only a notebook with some pencils) and the other in my hands. I think each unit weights about 6-7 Kg (so about 12-14-ish Kg total)... and I lugged those around to another class before heading back home/my college rental apt. So yeah... after carrying those things home, I felt my hands were somehow longer after that.

Oh, and the following day, I found an old, broken-apart HP 6291A lab power supply. That one was also quite heavy with its big hunkin' transformer inside. It didn't fit in my backpack, so I carried that one in hands as well.

Oh, the things I've done for picking up scrap electronics!

m2

I used to carry large Sony Trinitron CRT tvs and monitors.

Then my hands will pain for the next day.

I also remember when I found 5 cheap line interactive UPS and tried to take all of them in 2 shopping bags. Well, the ups tore apart the bags right when I arrived at the car. I was lucky this time.

Now that I am older I am not able to do this kind of things without having consequences at my arms and knees for several days..

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Now that I am older I am not able to do this kind of things without having consequences at my arms and knees for several days..

Same.

I'm not old by any means (just getting into my early 30's), but it's certainly not like being in my early-mid 20's, when I could do these things all day and not care about consequences, as there usually would be none.

Also, correction on the above statement I made about the APC UPS units that I found (if that matters to anyone) - it was 2x APC BackUPS CS 350 units and 1x APC BackUPS CS 650. The two 350's fit in my backpack, and the 650 I carried by hand... so that's a total of ~25 Kg split between backpack and in hands, lol. I only remembered when I looked back at the pictures of the UPSes I had. But I guess if I couldn't remember before that, then they must have not been that heavy.

Now carrying the two Sony GDM-FW900 monitors from the person that was giving them out to my car (about 10-15-ish meters / yards) - those I remember! At 45 Kg (almost 100 lbs) each, it's hard to forget them.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Let us know when you get to the 2nd set. Curious to see what that one was like for you to be shaking your head like that.

Well, finally got around to starting to dig into the second one (i'm moving house in the next couple weeks too), and......

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

^^This would be the stage where I announce our sponsor: PCBWaaaaaaaay

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

^^This would be the stage where I announce our sponsor: PCBWaaaaaaaay

To quote AvE (look him up on YouTube, it's pure and utter GOLD) - "That's too much like cheatin'..."

Besides, i wanna get this done tonight, these are part of a delayed one-year anniversary gift to my wonderful girlfriend, and i meant / hoped to finish rebuilding both power supplies on tuesday, but it just wasn't meant to be

But yeah, i'm not afraid of running a couple of wires here and there, if it saves me weeks of waiting and who knows how many more tens (if not hundreds) of dollars

I probably won't have time to do a blog write-up about this second one earlier than late-june, but it WILL get done eventually

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

It was past midnight last night (with my alarm about to go off at 5:50am to get up for work), but i got it done! And, of course (?), all is well and working fine

A piece of solder-drenched solder-wick here, a (thick-ish) resistor leg there, solder-resist scrapef off etc...

As part of the rebuild, i also stuck in two pairs of Teapo LXK 680u/200v caps on the primary, "for good measure".

But it's done!

I "couldn't" sell these even if i wanted to (to make it worth the time and effort), so it's just as well they'll be part of the anniversary gift to my significant other

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well, finally got around to starting to dig into the second one (i'm moving house in the next couple weeks too), and......

WOW!
That PCB sure has seen better days. Not talking about the wires on the bottom here - while they aren't a great job from the original owner, they aren't terrible either. What really intrigues me here is how many components have let out their magic smoke - particularly that one TO-92 transistor in spot Q4. It's like someone took a bite right out of it. Must have been quite the sight to see when the whole board went off.

A piece of solder-drenched solder-wick here, a (thick-ish) resistor leg there, solder-resist scrapef off etc...

As part of the rebuild, i also stuck in two pairs of Teapo LXK 680u/200v caps on the primary, "for good measure".

But it's done!

Not bad at all!

It's classes above this ghetto trace repair job I did... which still works!

But yeah, i'm not afraid of running a couple of wires here and there, if it saves me weeks of waiting and who knows how many more tens (if not hundreds) of dollars

Exactly! Besides, as long as it holds up fine, no one will really care what it looks like on the inside. Obviously just need to make the trace connections/repairs secure against vibration, in case your significant other really decides to get jammin' a bit louder some day.

I probably won't have time to do a blog write-up about this second one earlier than late-june, but it WILL get done eventually

Well, better than my repairs posting "schedule". I have stuff/pictures that I've been meaning to post for several years now... and just kept pushing to the back when I'd get more stuff to repair. At least most of my repairs are junky crap no one cares about, so not a big loss, I guess. But judging by the popularity of this thread, I'd say these Alesis M1's are still valued by people, even if they don't really sell well.

It was past midnight last night (with my alarm about to go off at 5:50am to get up for work), but i got it done! And, of course (?), all is well and working fine

6 AM is when I go to sleep sometimes (well, especially moreso now when I'm out of a job, lol. ) I really can't deal with waking up early, though - takes my brain several hours to "warm up". After that, all good until midnight or so.

[ryanz9752]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Found this thread while searching for repair knowledge on the MKII, was surprised to know there are still so many people interested in these speakers(it has been more than a decade, obviously).

I recently acquired a pair of MKIIs, one in working order with some water damage to the cabinet, while the other one won't turn on. Took both apart and found the working one has a lot of bulging caps.

The bad one has exploded F1 R11 R15 and Q3, which seems to suggest a short in Q1. This one also has been repaired at least once before, it have exactly same burnt traces as LuigiDJ posted in 2011. These were fixed with some soldered-on wires, and D1~D4 D14 D16 were replaced. C6 C7 C8 were replaced with Nippon-Chemicon ones but C8 is already bulging again. A small fire was started obviously and part of the acoustic material has been consumed by the fire, nothing too serious luckily.

I think what I will do is try to fix the water damage first. I plan to scrape out and sand down the swelled MDF, use epoxy to stabilize it, and use some filler before sanding and re-vinyl.

For the electronics, I will replace all electrolytic caps in the good one, move C8 to C14. The bad one probably needs the whole chain of components replaced, and the series light bulb method for testing(hard to find tungsten these days).

I will post back when I have made some progress(have been busy these days). This is a wonderful thread. Thanks everyone for providing their part of information.

[ryanz9752]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I have good news, I successfully repaired my Mk2s and they have been powered on for a month or so without any problem. Sounds very nice, especially the bass are very impressive for woofer of this size.

I basically followed my plan and things mostly went OK. I repaired the water damage by removing part of the panel with burrs, then filled it back to shape with wood flour and epoxy, with the help of 3D-printed mock back plate. Replaced the ferrofluid in tweeters with APG L11 low viscosity FF, put in new polyfill, and 3D printed a new plate for one of the audio input jack.

For the burnt PSU board, apart from obviously bad parts, I replaced UC3842 with newer UC3842B, MOSFETs with 600V 10A ST MOSFETs in plastic TO-220 package, D14 D16 with SF18G 600V 35ns, optocoupler with CNY17-4. All primary side silicon parts, NTC resistor, and any other parts that may have been damaged were replaced for good measure. There was one via on the ground trace which was vaporized and had to be plugged. Both speakers had R3 R4 47K increased to 68K, C8 to C14, and fuses changed to 3.15A slow-blow. All electrolytic caps on both amp and PSU boards of both speakers were replaced with either Chemi-Con, Rubycon or Nichicon ones.

During reassembling I found the screws on the amp board holding the amp IC to the heatsink were extremely hard to screw in. So I drilled the hole to 3mm and used M3 nuts and screws instead of the original self-tapping rubbish. New thermal compound were applied (I used leftover Arctic MX4 which was way overkill). All tall parts were reinforced with RTV silicon rubber(flapping in the breeze is never a good idea, especially as this is a loudspeaker which always vibrates).

Tested with series bulb, without incident. The bulb never did fully light up and no magic smoke were released. Although I failed to realize that this PSU may not run properly under no load, which created some confusion when I first started to test. Everything worked fine after I hooked up the amp board.

Here are some photos.

[cmcltd]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I response to the question about the schematic for the M! Active reference monitor.
Has anyone replied? I need that schematic, or parts list. It is the older one than what is readily available online.
3 caps are bad on mine, and they are the past on type, which have disintegrated, so I have no way of checking the values.
The board is the 9-40-1386-A
Alesis tech support could not help. How does that work? Factory doesn't have their own schematics?? Any help here would be great.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

You might consider posting some photos here, perhaps some of us can recognize or deduce what their values might have been.

In the mean time, might this help?

[Skeeter]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Help!

I have read through this long group of help by so many of you - thank you! I have a matched pair of Alesis M1 Active 1st generation studio monitors. Monitor #1 works just fine, and Monitor #2 has the flashing blue led. So, I replaced the following on Monitor #2 power supply board:
1. C8 with 330uF (according to recommendations from other writers)
2. C38 with 220pf (because it looked like it on the back side of the circuit board that it may have heat evidence from R27)
3. R27 with 100 Ohm
4. R3 with 47K Ohm
5. R4 with 47K Ohm
6. R15 with 0.22 Ohm
However, I still have the flashing blue led on Monitor #2 and no sound.
I swapped the power supply board from Monitor #1 onto Monitor #2, and it works just fine, so I am confident that I still have a issue on the Monitor #2 power supply board. No other areas appear to have heat evidence.
Can you please help me?

Thank you!

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Welcome to Badcaps Skeeter!
Please post some good in focus detailed pictures of your power board, maybe we will notice something you have not.
Also list what manufacturer and model of cap you used to replace C8.

[Skeeter]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Per Hansson:
Thank you very much. Please find 8 photos attached. The blackened areas of the bottom of the board were originally somewhat blackened, but my humble work to de-solder and re-solder darkened them further. I also had to bridge a couple of tracers due to my poor de-soldering skills, but I tested the connections and they are just right.

The C8 Capacitor (along with the other parts) was purchased from Digi-Key. The C8 is Panasonic, MFG# EEU-FR1V331UB, CAP ALUM 330 UF 20% 35V RADIAL TH.

Thank you for your kind help!

Skeeter

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

The blue LED has a direct connection to the power board and has nothing to do with the actual board the connector is on.
So if it is flashing it probably means the UC3844N is shutting down because it senses overload condition, then restarting again.

Referring to the schematic posted by Khron in post #29 you need to check basic voltages:

Start after the bridge rectifier, for example across negative of C7 and positive of C8, you should have around 325VDC.
If you do then check across UC3844N pin 5 GND and pin 7 VCC, you should have around 15VDC, you can also measure this across C8 instead if it is more convenient.
If you do then measure all voltages on the connector that goes over to the PWRAMP/XOVER PCB board.

P.S: Did any of the resistors you replaced measure bad, or why did you replace them?