Repairing Alesis M1 Active mk2 Monitor Speakers

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

One more thing: did you check C6 that you mentioned in the post quoted above?

Updates...

I was supposed to work some more on this Sunday but She Who Must Be Obeyed decided she wanted to paint the kitchen, so there's that...

The top of C6 capacitor feels like a firm bubble, meaning I can push it down and it springs back up.

The noise is loud enough to hear, especially when turning the unit off. Not sure if you can hear the sustained tone in the video but you can most definitely hear it when it turns off... https://photos.app.goo.gl/HboTvjY7sfEbCBpJ6

Audio signal does *not* pass through.

I'm at the point now where I'd like to ask if anyone wants to try and fix it for me? I have two speakers that work so I can get back to rebuilding my studio now.

I was wondering, though, since all you guys have experience with these speakers, are you audio engineers too?

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

You can try to pinpoint where the noise comes from, if it is from the new inductor try to put the old one back like I mentioned in a previous post.

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

The top of C6 capacitor feels like a firm bubble, meaning I can push it down and it springs back up.

It's probably just the plastic sleeve on top, then.
Still doesn't mean the cap can't be bad.
You can try removing it and seeing if there is any blue-green or brown corrosion near it's leads.
Another test is to take a 19V or 20V laptop power adapter and connect the adapter's (+) output to the cap's (+) lead along with the adapter's (-) output to cap's (-) lead. Basically, let the cap charge to 20V (it should be instant as soon as you connect the cap to the power adapter.) Then disconnect the cap and measure the voltage across it with a multimeter. It should have close to 20V or whatever the adapter outputs. If not, it's probably bad. Also, if you short-circuit the cap's leads with a metal object, you should see and hear a small spark. If no spark at all, cap might be high-ESR. With these high-voltage caps, though, they typically either go open-circuit or loose capacitance... and in rare instances, they may also go short-circuit. But if that was the case, the input fuse or something else would have popped.

The noise is loud enough to hear, especially when turning the unit off. Not sure if you can hear the sustained tone in the video but you can most definitely hear it when it turns off... https://photos.app.goo.gl/HboTvjY7sfEbCBpJ6

Audio signal does *not* pass through.

I can hear a high-pitched noise.

If the audio is not going through, though, that might be something on the amp side. Hard to say, though.

I'm at the point now where I'd like to ask if anyone wants to try and fix it for me? I have two speakers that work so I can get back to rebuilding my studio now.

Well, if you drive by the Northern Virginia (NoVA) or DC area, send me a PM. I'll be here for another month or two. Probably will need to start packing my bench in early April, if not before that. Could still take a look, though.

I was wondering, though, since all you guys have experience with these speakers, are you audio engineers too?

Well, I can't speak for the others here... but I've never touched or seen these speakers with my own eyes, other than through what's been posted here. I'm definitely a "wannabe" audio engineer . A real one - no. Just a hobbyist tech with an EET degree that's so far been very useful for keeping one of my audio amplifiers covered so it doesn't get dust in when I'm not using it.

[xfreakx]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I can't believe I've read through all the 26 pages of this thread.

First, thanks to everyone here, it helped me a lot to fix this problematic power supply. It took some time and 3 orders at the electronics shop but it's working now.

Someone replaced already the notorious C8 in a previous repair and the speakers were working for a while. As I got them, Q1 was cracked from overheating as well as Q4. R11 and R15 were black and Q2 and D5 shorted. C6 and C7 looked bloated so I replaced them as well. Fuse was alright (!).

After replacing this parts the power supply still didn't start, so I replaced U1, Q3, C8 and C35. Still no output. Compared to the other board in the working 2. speaker all the other transistors, diodes and resistors seemed fine.

Since most of the parts are cheap and available, I replaced U3, Q5 and D6 and the power supply started. 36 / 18V on output. Yay!

[biggertv]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yikes! Those Caps sitting right on the Heatsink...they're gonna be Toast. If there's any way to replace and extend leads to fold them over they will last much longer. Those designers will Never Learn!

[vintagevalves]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Joining the blown up M1A620 club. A pair of these were 'gifted' to me not working during Covid shutdowns. One required a C8 replacement and now works fine.

The other has been troublesome. After C8 replacement the power supply seems good with
High rails at 36.8V and low at 17.25. When all hooked up, the woofer pulsed a very loud square wave type sound. Original woofer got toasted by this prior to my ownership.

I removed the LM3886 for the woofer and the tweeter side seems stable without it in, though the gain pot seems intermittent (a separate issue?) Suspected a bad LM3886. They were very hard to get for a couple of years. I replaced with an NTE7179 which appeared to be equivalent, but still did not work. I was finally able to source a real LM3886TF and am doing some checks before putting it in.
Voltages as follow with no chip installed:

1: V+ - 36.8
2: NC
3: Output +1.0vdc
4: V- -36.8v
5: V+ 36.8v
6: Nc
7: Gnd 0
8: Mute -4v
9: Vin +1.0vdc
10: Vin + 0.3vdc
11: NC

The 1vdc on the input and output is concerning. Any suggestions on what to check next? Don't want to blow up this LM3886 that I waited SO long to get my hands on... Thanks!