Repairing Alesis M1 Active mk2 Monitor Speakers

[Khron]

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]

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]

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]

"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]

Originally Posted by Khron

"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.

Originally Posted by Khron

"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.

Originally Posted by Khron

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]

Originally Posted by momaka

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]

Originally Posted by goodpsusearch

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.