Repairing Alesis M1 Active mk2 Monitor Speakers

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok, sorry for the delay, I couldn't do anything until I got the bits and pieces...

No worries, we aren't going anywhere.

I have a new multimeter so now you guys can tell how to do what it is I need to do, if I even can with this one.

Well, like Per noted in post #479, you won't be able to measure an inductor's inductance with a multimeter... but that's OK. The multimeter is for checking all of the other components - namely diodes, resistors, and transistors on the board.

For starters, it's probably best that you check your multimeter's functions first. Connect black probe to "COM" jack and red probe to "V/Hz/Ohms/%/NCV...", then select the Ohms / continuity / diode check function (4th position after OFF on the rotary switch), and select resistance test mode (probably might have to press "Func." button to get to it, if it isn't the function selected already. After this short the probes together and note what resistance you get - this is your "short-circuit" resistance. Depending on multimeter and probes quality, this can be anywhere from 0.1 to 2-3 Ohms (sometimes even more, like those cheapo multimeters from HF.)

After this test, also check the voltage of 9V or 1.5V battery, just to make sure the voltage function on the MM is working too.

If all good, time to jump in and start checking components.

Let's start with diode D14, since that looks very close to where all of the "action" happened on the board.

Select diode test on your multimeter (little diode symbol should appear on the display), put red probe on the anode of D14 and black probe on the cathode of D14 (side with the white stripe). You should get about 560-700 mV reading on your screen (or 0.560 to 0.700V, depending on how your MM displays results.) If you get much lower than these values, note what they are and post them here, though you can do the same even if you do get readings in the above range, just as a 2nd check. Also note that this check on diode D14 tests transistor (MOSFET) Q2 across D-S junction. So if you get a really low reading across D14, take it out of the circuit and measure it again. If it measures OK out of circuit, Q2 could be bad.

Next, check resistor R15. It's a 0.22 Ohm resistor, so you should see more or less under 1 Ohms of resistance on your multimeter (again, depending on how low it can measure) when set on the resistance test setting. If R15 is open or showing very high resistance, then transistor Q1 is more than likely bad too.

If either D14 or R15 were bad above, remove them out of the circuit, then test Q1 and Q2. These are MOSFETs. With the MOSFET's front facing you (the side with the "IRF840" part number written on it), the left-most pin is the Gate, center is Drain, and right-most is Source. Use multimeter on resistance test and check resistance between Source-Drain, Source-Gate, and Drain-Gate. For Q1, you should get open (infinite resistance / 0L) for all tests, or very high resistance in the MegaOhm range. For Q2, same, except Source-Gate - should get about 10 KOhms resistance there. If you get any other values, definitely post them here. If you get low resistance readings (in the Ohms range), one or both of these is likely bad and you'd have to remove it/them to test out of circuit.

So let's start with those for now. And if you're comfortable with those and know what you're doing, you can skip ahead and also test Q3 & Q4 (these would be BJTs, so slightly different testing methodology.) I wrote how at the end of post #461:
https://www.badcaps.net/forum/showpo...&postcount=461

Next, notice the size difference in the old inductor and the new one! As far as glue, do you think I need it since the new one has that little base on it? And which kind of glue, hot melt?

Interesting.
Well, the wire turns on the new one appear to be of the same thickness, so that's a good sign. The smaller core, we will have to see about. Generally smaller core = less surface area to dissipate heat. But if the new smaller core heats up less to begin with, then it should be fine. It's going to be a bit of an experiment, like I said... hence why keep the old core until the speakers have been proven to work reliably and without anything overheating.

You don't necessarily need to glue the new inductor... but given how badly the trace and hole for it are eaten away on the PCB, it may not be a bad idea.

Hot glue should work OK, unless the inductor/PCB/surround electronics get really hot (over 60C), at which point the hot glue may become a little soft and not hold as well. On a side note, now you have a thermocouple probe to check temperatures with your new MM, so you can find out eventually.

I've also used regular household silicone/caulk, but that's not always recommended due to certain types/brands producing more acetic acid when they cure than others... and acetic acid is a mild corrosive. Still, even "the worst" silicones would be a million times better than the tan glue. The stuff I've used is the cheapest brand/type from Home Depot and doesn't seem to have corroded anything so far.

If you want to be fancy / proper, use electronics-grade RTV.

Other glues - read the fine print. Can't be anything (too) corrosive. Also usually not a good idea to use any solvent-based glues, particularly on inductors or anything with coated magnet wire, as that could strip/dissolve away the insulating coating and possibly short out turns.

Grinding down the cooked part of the PCB... what to use... a Dremel? Honestly doing that freaks me out more than putting the new pieces on the board!

Dremel with the finest attachment you have. Maybe a drill with a very small drill bit too. Any charred PCB has to go. When you get to clean... or at least overheated but not charred guts, you can stop then. And yes, that could certainly be one of the hardest parts of this fix. Just take your time with it slowly.

I took C8 out and I can see the positive (+) indicator on the board, but which is the (+) of the new cap?

On electrolytic capacitors, the negative side is marked with a vertical stripe. So the positive lead is the other side.

I also bought another monitor off eBay that's untested but the guy said in the listing that it powers on, so that's already better than the one I'm working on.

Great! More patients coming for this thread.
Hopefully that one won't have any issues (yet). But, see comment below.

For mine that does power on, I'm guessing I should go ahead and take its PCB out and clean up the yellow glue before it blows up as well.

Absolutely!
While at it, replace C8 and C35. It's only a matter of time before they fail too.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hmmm.
OK, now from the new pictures of the inductor, it does look like it might have overheated (the red color looks quite dark on one side, unless that's from the shadow/lights again.) IDK, hard to say. But once you get a MM, we will continue.

By the way, nice soldering station. I think I used either the same or a similar one at a previous job, and it works quite well. At least in regards to the soldering equipment, you look to be all set.


Agreed.

Will probably need to cut / drill / grind away as much of the black / dark sooth as possible. It can be conductive too, otherwise. Had to scrap a laptop motherboard due to this, as it kept arcing between traces. Your board should be salvageable, though, because there aren't any super-fine traces like there are on laptop boards, and yours is also only a 2-layer board.


+1

You can also glue the inductor to the board. Just don't use that same tan/yellow conductive glue that the manufacturers did.


I second this.

Those caps don't usually go bad... but if they did, just find an old cheap junk ATX PSU (anything that has a red 115/230V selection switch.) Those will usually have similar caps you can use, at least for a test.

Ok, sorry for the delay, I couldn't do anything until I got the bits and pieces...

I have a new multimeter so now you guys can tell how to do what it is I need to do, if I even can with this one.

Next, notice the size difference in the old inductor and the new one! As far as glue, do you think I need it since the new one has that little base on it? And which kind of glue, hot melt?

Grinding down the cooked part of the PCB... what to use... a Dremel? Honestly doing that freaks me out more than putting the new pieces on the board!

I took C8 out and I can see the positive (+) indicator on the board, but which is the (+) of the new cap?

I also bought another monitor off eBay that's untested but the guy said in the listing that it powers on, so that's already better than the one I'm working on.

For mine that does power on, I'm guessing I should go ahead and take its PCB out and clean up the yellow glue before it blows up as well.

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hmmm.
OK, now from the new pictures of the inductor, it does look like it might have overheated (the red color looks quite dark on one side, unless that's from the shadow/lights again.) IDK, hard to say. But once you get a MM, we will continue.

By the way, nice soldering station. I think I used either the same or a similar one at a previous job, and it works quite well. At least in regards to the soldering equipment, you look to be all set.

Your worst problem seem to be the burnt circuit board.

Agreed.

Will probably need to cut / drill / grind away as much of the black / dark sooth as possible. It can be conductive too, otherwise. Had to scrap a laptop motherboard due to this, as it kept arcing between traces. Your board should be salvageable, though, because there aren't any super-fine traces like there are on laptop boards, and yours is also only a 2-layer board.

But you might be able to be creative and extend the leg of the inductor to reach another hole on the same trace, or solder it to the broken trace and secure it some other way.

+1

You can also glue the inductor to the board. Just don't use that same tan/yellow conductive glue that the manufacturers did.

About the large capacitors, it might just be the plastic top of C6 that is convex, see if you can easily push it down with your thumb...

I second this.

Those caps don't usually go bad... but if they did, just find an old cheap junk ATX PSU (anything that has a red 115/230V selection switch.) Those will usually have similar caps you can use, at least for a test.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

That looks much better! Your worst problem seem to be the burnt circuit board.
But you might be able to be creative and extend the leg of the inductor to reach another hole on the same trace, or solder it to the broken trace and secure it some other way.
That said I attached a picture of an area that is of concern, it looks to me like leg 2 of the UC3842 controller has overheated.
There is also to its bottom left in the picture some more burn marks on the PCB.
In this instance I would do either of two things:
1: Get a multimeter and check the diode D9 and D14
2: Wire an incandescent light bulb in series with the live wire and turn the set on after soldering back all components.

About the large capacitors, it might just be the plastic top of C6 that is convex, see if you can easily push it down with your thumb...

i think what you saw was a shadow. Here's another picture with better light on the area...

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

That looks much better! Your worst problem seem to be the burnt circuit board.
But you might be able to be creative and extend the leg of the inductor to reach another hole on the same trace, or solder it to the broken trace and secure it some other way.
That said I attached a picture of an area that is of concern, it looks to me like leg 2 of the UC3842 controller has overheated.
There is also to its bottom left in the picture some more burn marks on the PCB.
In this instance I would do either of two things:
1: Get a multimeter and check the diode D9 and D14
2: Wire an incandescent light bulb in series with the live wire and turn the set on after soldering back all components.

About the large capacitors, it might just be the plastic top of C6 that is convex, see if you can easily push it down with your thumb...

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hmm.. yeah definitely looks a lot worse from this side - at least the wire definitely appears to be toast.

If the core hasn't overheated when the failure happened (and that's the hard-to-tell part), you might be able to rewind it. But at that point, since you probably will be ordering new capacitors and possibly other parts, then you might as well get the inductor you found on Mouser... unless of course you just want to try rewinding the old inductor for fun/experience. But even then, I suggest getting the one from Mouser, just as insurance... or at least so that if you find you need it later, you won't have to pay separate shipping just for this part. Don't discard the old inductor yet either - not until the speakers are fixed and verified working, just in case.


IC = integrated circuit (i.e. chip)
UC3844 / UC3842 = literally the "heart" of this power supply - it drives the main switches (MOSFETs) On and Off to produce power on the secondary side of the PSU.


Well, if you plan on doing some electronics repairs once in a while, it may be worthwhile to get something better. Of course, even something like the cheapest bottom-dollar multimeters from Harbor Freight can do the job in most cases... but I don't really recommend those. Even new, they sometimes come with issues and quirks that can throw you off if you're new to electronics repair and troubleshooting. Also, you can get more for your money online (unless you get those HF meters for free with a coupon... but again, they do have some "quirks" even when new.)

I haven't tested or tried any of these, but they all will likely be better quality than the HF multimeters:
https://www.ebay.com/itm/285029877100
https://www.ebay.com/itm/364050575003
https://www.ebay.com/itm/234846288590
https://www.ebay.com/itm/363898735461
https://www.ebay.com/itm/224527285180
https://www.ebay.com/itm/195144875873


Most non-specialty multimeters won't measure inductance, as Per mentioned.

For that, the cheapest alternative tool would be one of these "component tester" / "transistor tester" meters. Something like these two:
https://www.ebay.com/itm/175517183133
https://www.ebay.com/itm/165703837398

(Note: the ones listed above may not necessarily offer the most/best features or the best price. There is a HUGE variety of these online... and if you're not in a hurry, you can get one slightly cheaper with shipping from China, but it's going to take a while to get here. *EDIT* Also, I wasn't aware the chip shortage has affected these, so probably a very good idea to check out the links that Per posted above.)

These component/transistor tester can test inductance.
Though in my experience, they are still a little limited when it comes to computer motherboard and GPU inductor testing, since they don't usually cover the very low uH range. Mine, for example, won't register below 0.01 to 0.02 mH (i.e. 10-20 uH) So with the 25 uH inductor in these Alesis speakers, mine may not be able to measure it too accurately. But some of the newer testers with updated firmware can.

With that said, just see what fits your needs - i.e. do you plan to do more electronics repair in the future? If so, grabbing one of these transistor/component testers can be a great tool for checking for bad electrolytic capacitors, and that's what I use mine for most of the time. On the other hand, if these speakers are the only repair you're expecting to do, then probably just get a multimeter only.


Yes, get off everything that looks burned.
And when you get a multimeter, we can look into more of the components in detail.


I'm with you on that one.

OK... so here's what the board looks like without L4 and D14...

And here's the inductor...

To me, Q3, Q4, C15, and D9 all look fine.

Also, in the section with C8 that I've already taken out, C6 is rounded/puffy at the top while C7 is flat. The guy at the pro audio place said he'd replace both of those as well. Both of those have the yellow (now brown) glue on them as well.

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Still think it's fixable? The inductor L4 looks like toast to me, but you guys know a ton more than I do!

Hmm.. yeah definitely looks a lot worse from this side - at least the wire definitely appears to be toast.

If the core hasn't overheated when the failure happened (and that's the hard-to-tell part), you might be able to rewind it. But at that point, since you probably will be ordering new capacitors and possibly other parts, then you might as well get the inductor you found on Mouser... unless of course you just want to try rewinding the old inductor for fun/experience. But even then, I suggest getting the one from Mouser, just as insurance... or at least so that if you find you need it later, you won't have to pay separate shipping just for this part. Don't discard the old inductor yet either - not until the speakers are fixed and verified working, just in case.

Oh, and I have no idea what the UC3844 IC even is...

IC = integrated circuit (i.e. chip)
UC3844 / UC3842 = literally the "heart" of this power supply - it drives the main switches (MOSFETs) On and Off to produce power on the secondary side of the PSU.

I'm looking at getting another but don't want to break the bank on one. Anything specific I should be looking for as far as functionality?

Well, if you plan on doing some electronics repairs once in a while, it may be worthwhile to get something better. Of course, even something like the cheapest bottom-dollar multimeters from Harbor Freight can do the job in most cases... but I don't really recommend those. Even new, they sometimes come with issues and quirks that can throw you off if you're new to electronics repair and troubleshooting. Also, you can get more for your money online (unless you get those HF meters for free with a coupon... but again, they do have some "quirks" even when new.)

I haven't tested or tried any of these, but they all will likely be better quality than the HF multimeters:
https://www.ebay.com/itm/285029877100
https://www.ebay.com/itm/364050575003
https://www.ebay.com/itm/234846288590
https://www.ebay.com/itm/363898735461
https://www.ebay.com/itm/224527285180
https://www.ebay.com/itm/195144875873

Can I measure inductance on a multimeter, and what should it read if I can, 25uH I'm guessing?

Most non-specialty multimeters won't measure inductance, as Per mentioned.

For that, the cheapest alternative tool would be one of these "component tester" / "transistor tester" meters. Something like these two:
https://www.ebay.com/itm/175517183133
https://www.ebay.com/itm/165703837398

(Note: the ones listed above may not necessarily offer the most/best features or the best price. There is a HUGE variety of these online... and if you're not in a hurry, you can get one slightly cheaper with shipping from China, but it's going to take a while to get here. *EDIT* Also, I wasn't aware the chip shortage has affected these, so probably a very good idea to check out the links that Per posted above.)

These component/transistor tester can test inductance.
Though in my experience, they are still a little limited when it comes to computer motherboard and GPU inductor testing, since they don't usually cover the very low uH range. Mine, for example, won't register below 0.01 to 0.02 mH (i.e. 10-20 uH) So with the 25 uH inductor in these Alesis speakers, mine may not be able to measure it too accurately. But some of the newer testers with updated firmware can.

With that said, just see what fits your needs - i.e. do you plan to do more electronics repair in the future? If so, grabbing one of these transistor/component testers can be a great tool for checking for bad electrolytic capacitors, and that's what I use mine for most of the time. On the other hand, if these speakers are the only repair you're expecting to do, then probably just get a multimeter only.

Should I just take all the burn looking pieces off now or wait?

Yes, get off everything that looks burned.
And when you get a multimeter, we can look into more of the components in detail.

Ok, so I took some time with some of the IPA you guys are talking about and cleaned up the board. I had a Pilsner by my side as I prefer that over IPA.

I'm with you on that one.

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I *had* a very nice multimeter that I carried with me when I was in the Navy and running audio all over the world... but I've lost it. I'm looking at getting another but don't want to break the bank on one. Anything specific I should be looking for as far as functionality?

It really depends on your budget, there are some decent meters from China nowdays if the budget is limited...
At a minimum it should have a diode check function though.

Can I measure inductance on a multimeter, and what should it read if I can, 25uH I'm guessing?

No, most multimeters will in general not measure inductance.
You need an LCR meter for that, a more expensive toy...
It also needs to be tested at the correct frequency, in this case 100kHz.
A cheap way to test it is with what is called the "component tester" (an open source project).
But a large issue with that right now is that due to component shortage the Chinese muppets have released inferior versions with fake Atmega chips.
Here is an example at least for what they look like:
https://www.eevblog.com/forum/testge...1/#msg4611991]
Here is a good video that shows how the (genuine) version works: https://youtu.be/bRtLkQ8dOj0

Should I just take all the burn looking pieces off now or wait?

Thanks for the help!

Yes, take off as much as you can so we see how it looks after thorough cleaning.
Also try to take a picture from the front of transistors Q3 and Q4 so we can see if they are ok after cleaning.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Do you have a multimeter?
The next suggestion will depend on that.

I *had* a very nice multimeter that I carried with me when I was in the Navy and running audio all over the world... but I've lost it. I'm looking at getting another but don't want to break the bank on one. Anything specific I should be looking for as far as functionality?

Remove the remaining glue from between the legs of U2 on the very top left of this picture:
https://www.badcaps.net/forum/attach...9&d=1673633160

Done.

Incidentally in the same picture to the very right is your control IC UC3844, however yours like many others here use a UC3842, with marking 3842 on the 8-pin chip...


I agree that it looks pretty bad, impossible to tell really without measuring the inductance.

Can I measure inductance on a multimeter, and what should it read if I can, 25uH I'm guessing?

Should I just take all the burn looking pieces off now or wait?

Thanks for the help!

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Do you have a multimeter?
The next suggestion will depend on that.

Remove the remaining glue from between the legs of U2 on the very top left of this picture:
https://www.badcaps.net/forum/attach...9&d=1673633160

Oh, and I have no idea what the UC3844 IC even is...

Incidentally in the same picture to the very right is your control IC UC3844, however yours like many others here use a UC3842, with marking 3842 on the 8-pin chip...

Still think it's fixable? The inductor L4 looks like toast to me, but you guys know a ton more than I do!

I agree that it looks pretty bad, impossible to tell really without measuring the inductance.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Looking at your pictures, I don't think you need to replace this inductor... unless once you take it off, you notice that all of the wires on the bottom are burned out and shorted together from the glue. But it looks like the tape protected the wires OK. At most, you might just have to unwind 1 turn of the wire where it burned or just cut the badly charred part and solder in new wire.

The other reason I suggest to use the original inductor is because I'm not sure how well the core properties on the inductor you found on Mouser would match to the one that's in the PSU already. After all, it's not just the inductance and the average/max current that matter. Al and frequency characteristics matter too.

Looking at the one on Mouser, it appears to be rated/tested for up to 150 KHz and this PSU has a UC3844 IC (which generally runs around 50 KHz... i.e. lower.) This means the Mouser replacement *might* actually work. But going with the original is probably the safer route, since it doesn't appear to be damaged at all, aside from the final turn going into the PCB.


Sounds like a plan.

And no, save the IPA beer for a party after fixing these speakers.

In electronics repair, IPA = IsoPropyl Alcohol


Yeah, a lot of electronics and computer repairs shops do this. I'm not a fan of this practice... but then I also don't do this for a living.

That said, $75 is a little bit much on the high side, IMO.


Skip the wick, unless you're already used to using it. I prefer to clean PCB holes with just a stainless steel needle - heat the via/hole on one side with the soldering iron and push through with the needle on the other side. Cork board / office board tacks work well too, though they are a little thicker and won't fully go through (except on very large vias / holes.)


Well, sounds like you have at least some experience with a soldering iron, so should be OK. Just give yourself time to do this. I think the more challenging part would be removing the tan glue where it hasn't baked-on yet. Some people here suggest IPA. I personally just tackle it with needle-nose pliers, small (and sharp) flat-heat screwdrivers, wire cutters / strippers, and heavy-duty tweezers - basically anything that is sharp and pointy and can grab stuff.


Sounds good!


Thanks for pointing these out. I dismissed D9 to be a resistor when I originally looked at the photos. But now that you brought it to my attention, it looks like D9 really might have taken a hit... and if it did, Q1, Q3, and Q4 could be toast too, as well as the UC3844 IC. C15 looks pretty bad too, and it too is part of that drive circuit. Depending on how conductive the glue went, even optocoupler U2 might have taken a hit.

Man, the glue in these speakers really is one of the more potent variants I've seen. I've had it in a number of PSUs for years where it has turned a crispy dark brown and still not become conductive enough to wreck anything.


Yeah, could be.

Though realistically speaking, it could also be that this glue is cheaper than hot glue. Or maybe they had issues with their industrial hot glue guns clogging or malfunctioning and thus moving onto something else. And hot glue does become soft with elevated temperatures, so maybe they had problems with that when wave-soldering? Or it could be a combination of all of these. But who knows.

Either way, I stand by my words that there's no way at this point, that PCB manufacturers can say that they didn't know this tan/yellow glues is not suitable for electronics. They DO know. Just no one cares, except for making things at the lowest cost possible and keeping "the wheel turning" by selling electronics that are bound to fail sooner rather than later.

Ok, so I took some time with some of the IPA you guys are talking about and cleaned up the board. I had a Pilsner by my side as I prefer that over IPA. but that's beside the point.

Still think it's fixable? The inductor L4 looks like toast to me, but you guys know a ton more than I do!

Oh, and I have no idea what the UC3844 IC even is...

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Thanks for the response and input! Over the last couple days I've been scouring the web for replacement parts and am pretty sure I'm going to need to replace that inductor at L4. I found this on mouser.com (https://www.mouser.com/ProductDetail...GrAAAO0g%3D%3D) and am wondering if this will work as a replacement? The Alesis tech manual for these says it's an Inductor Resonant 25uH 3A. The original is just the loop help in place by the exploded goop and the one at mouser has that little base on it.

Looking at your pictures, I don't think you need to replace this inductor... unless once you take it off, you notice that all of the wires on the bottom are burned out and shorted together from the glue. But it looks like the tape protected the wires OK. At most, you might just have to unwind 1 turn of the wire where it burned or just cut the badly charred part and solder in new wire.

The other reason I suggest to use the original inductor is because I'm not sure how well the core properties on the inductor you found on Mouser would match to the one that's in the PSU already. After all, it's not just the inductance and the average/max current that matter. Al and frequency characteristics matter too.

Looking at the one on Mouser, it appears to be rated/tested for up to 150 KHz and this PSU has a UC3844 IC (which generally runs around 50 KHz... i.e. lower.) This means the Mouser replacement *might* actually work. But going with the original is probably the safer route, since it doesn't appear to be damaged at all, aside from the final turn going into the PCB.

Once I take off L4 and clean it up (using IPA beer?) I'll take some more pictures.

Sounds like a plan.

And no, save the IPA beer for a party after fixing these speakers.

In electronics repair, IPA = IsoPropyl Alcohol

I took the board to a pro audio place today and they were like, well, we can look at it but as soon as it hits the guy's desk it'll cost you $75. WTH... $75 just to look at the stupid thing??

Yeah, a lot of electronics and computer repairs shops do this. I'm not a fan of this practice... but then I also don't do this for a living.

That said, $75 is a little bit much on the high side, IMO.

Time to get on Amazon and order desoldering wick because RadioShack doesn't exist anymore...

Skip the wick, unless you're already used to using it. I prefer to clean PCB holes with just a stainless steel needle - heat the via/hole on one side with the soldering iron and push through with the needle on the other side. Cork board / office board tacks work well too, though they are a little thicker and won't fully go through (except on very large vias / holes.)

I've never done work on a board like this before and the extent of my soldering is limited to making microphone cables, speaker cables, and instrument cables.

Well, sounds like you have at least some experience with a soldering iron, so should be OK. Just give yourself time to do this. I think the more challenging part would be removing the tan glue where it hasn't baked-on yet. Some people here suggest IPA. I personally just tackle it with needle-nose pliers, small (and sharp) flat-heat screwdrivers, wire cutters / strippers, and heavy-duty tweezers - basically anything that is sharp and pointy and can grab stuff.

I'll keep y'all updated.

Sounds good!

I would also already do a diode forward voltage test of D14 and D9 as they look terrible in your pictures and if they are bad more components might be bad...

Thanks for pointing these out. I dismissed D9 to be a resistor when I originally looked at the photos. But now that you brought it to my attention, it looks like D9 really might have taken a hit... and if it did, Q1, Q3, and Q4 could be toast too, as well as the UC3844 IC. C15 looks pretty bad too, and it too is part of that drive circuit. Depending on how conductive the glue went, even optocoupler U2 might have taken a hit.

Man, the glue in these speakers really is one of the more potent variants I've seen. I've had it in a number of PSUs for years where it has turned a crispy dark brown and still not become conductive enough to wreck anything.

P.S: It is funny to look back at the very early board that member Skeeter posted. (Linked below).
There Alesis used the sensible normal hot glue to hold everything and 22 years later it still looks fine.
Guess they figured that wont sell any new units so lets switch to the conductive tan/yellow glue!
https://www.badcaps.net/forum/showpo...&postcount=399

Yeah, could be.

Though realistically speaking, it could also be that this glue is cheaper than hot glue. Or maybe they had issues with their industrial hot glue guns clogging or malfunctioning and thus moving onto something else. And hot glue does become soft with elevated temperatures, so maybe they had problems with that when wave-soldering? Or it could be a combination of all of these. But who knows.

Either way, I stand by my words that there's no way at this point, that PCB manufacturers can say that they didn't know this tan/yellow glues is not suitable for electronics. They DO know. Just no one cares, except for making things at the lowest cost possible and keeping "the wheel turning" by selling electronics that are bound to fail sooner rather than later.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi jgulyas, welcome to the forum!

Oof, that does look pretty crispy. But it should still be fixable. It looks like a case of the tan/yellow glue gone conductive again.

Essentially, because the electronics in these speakers may endure vibrations (due to being mounted inside the cabinet of the speaker), manufacturers of such speakers often put glue on some of the bigger components to help stabilize them. And it also helps keep these bigger components in place when being soldered during manufacturing.

I'm not sure if some manufacturers are doing these deliberately or not (be it to save on costs or really just planned obsolescence), but many still use some form/variant of this yellow/tan glue, which is not suitable for electronics at all. The problem with this glue is that it goes conductive over time, especially when mixed with heat and/or high humidity (which, you being a fellow Virginian, I'm sure you know about in the summer ). When this glue goes conductive... well, you see the results. They are not always this spectacular... and to some extent, that probably also depends on the glue manufacturer itself (like I said, different variants), but we've seen it wreck a great number of electronics over the years.

In fact, if you read just a few posts above where zinger5 started his discussion, you'll see he ran into the same problem, albeit with much less damage. In his case, it was the glue going conductive between two pins on the UC3844 PWM IC (posts #465 and 468.)

Not only does this glue go conductive, but some of its variants are also highly corrosive... which again is a big no-no in electronics, as it can eat away at traces and component leads.

Thus, it's probably best that you remove as much of it as possible - especially on the primary side or anywhere with high(er) voltages or in contact with component leads. Once you have all of the glue and black sooth cleaned up, consider replacing C8 and C35, as those are usually the first capacitors to go bad. And also a good idea to use a 100-300 Watt halogen bulb in series with the live when testing the PSU to prevent further damage, once the PSU is at a point where we think it's "fixed". But we'll get there. First do the clean up and post some pictures so we can see how bad the damage is and what to possibly check.

On that note, zinger5, if you're still reading this, you might want to go back to that speaker that was fixed in post #468 and also remove as much glue as possible from underneath your inductor. Seems the glue used in these Alesis speakers really is more "potent" than others.

Thanks for the response and input! Over the last couple days I've been scouring the web for replacement parts and am pretty sure I'm going to need to replace that inductor at L4. I found this on mouser.com (https://www.mouser.com/ProductDetail...GrAAAO0g%3D%3D) and am wondering if this will work as a replacement? The Alesis tech manual for these says it's an Inductor Resonant 25uH 3A. The original is just the loop help in place by the exploded goop and the one at mouser has that little base on it.

Once I take off L4 and clean it up (using IPA beer?) I'll take some more pictures. I took the board to a pro audio place today and they were like, well, we can look at it but as soon as it hits the guy's desk it'll cost you $75. WTH... $75 just to look at the stupid thing??

Time to get on Amazon and order desoldering wick because RadioShack doesn't exist anymore...

I've never done work on a board like this before and the extent of my soldering is limited to making microphone cables, speaker cables, and instrument cables.

I'll keep y'all updated.

John

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Agree 100% with what momaka said.
I would also already do a diode forward voltage test of D14 and D9 as they look terrible in your pictures and if they are bad more components might be bad...

P.S: It is funny to look back at the very early board that member Skeeter posted. (Linked below).
There Alesis used the sensible normal hot glue to hold everything and 22 years later it still looks fine.
Guess they figured that wont sell any new units so lets switch to the conductive tan/yellow glue!
https://www.badcaps.net/forum/showpo...&postcount=399

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi jgulyas, welcome to the forum!

Oof, that does look pretty crispy. But it should still be fixable. It looks like a case of the tan/yellow glue gone conductive again.

Essentially, because the electronics in these speakers may endure vibrations (due to being mounted inside the cabinet of the speaker), manufacturers of such speakers often put glue on some of the bigger components to help stabilize them. And it also helps keep these bigger components in place when being soldered during manufacturing.

I'm not sure if some manufacturers are doing these deliberately or not (be it to save on costs or really just planned obsolescence), but many still use some form/variant of this yellow/tan glue, which is not suitable for electronics at all. The problem with this glue is that it goes conductive over time, especially when mixed with heat and/or high humidity (which, you being a fellow Virginian, I'm sure you know about in the summer ). When this glue goes conductive... well, you see the results. They are not always this spectacular... and to some extent, that probably also depends on the glue manufacturer itself (like I said, different variants), but we've seen it wreck a great number of electronics over the years.

In fact, if you read just a few posts above where zinger5 started his discussion, you'll see he ran into the same problem, albeit with much less damage. In his case, it was the glue going conductive between two pins on the UC3844 PWM IC (posts #465 and 468.)

Not only does this glue go conductive, but some of its variants are also highly corrosive... which again is a big no-no in electronics, as it can eat away at traces and component leads.

Thus, it's probably best that you remove as much of it as possible - especially on the primary side or anywhere with high(er) voltages or in contact with component leads. Once you have all of the glue and black sooth cleaned up, consider replacing C8 and C35, as those are usually the first capacitors to go bad. And also a good idea to use a 100-300 Watt halogen bulb in series with the live when testing the PSU to prevent further damage, once the PSU is at a point where we think it's "fixed". But we'll get there. First do the clean up and post some pictures so we can see how bad the damage is and what to possibly check.

On that note, zinger5, if you're still reading this, you might want to go back to that speaker that was fixed in post #468 and also remove as much glue as possible from underneath your inductor. Seems the glue used in these Alesis speakers really is more "potent" than others.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Here are the pics that I forgot...

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi Folks,

Just joined and have been reading up on how to repair these things. I have an issue that I don't think has been brought up yet. I bought a set of these monitors knowing that one of them had the issue with the blinking light so I've been prepared to do a little bit of work to have a great set of monitors. When I took the board out I noticed on mine that it looks like there was an explosion at L4.

Is this fixable??

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

The only thing I've noticed on the rear of the board is a little corrosion (?) between pins 1 & 2 of the UC3844N. That's the close up picture of the rear of the board attached. Might that be causing a short or be an indication of the IC having sustained damage/worn out?

Looks like leftover flux from the factory soldering... but then it's also odd that this would be the only spot to have it while the rest of the board looks pretty clean.

Well, that turned out to be a very good shout - a rub down with some IPA to clean up those points on the rear of the board and it's powered up and working perfectly!

To me it looks exactly like the yellow glue elsewhere on the set that Momaka explains becomes conductive, but why it would be there on the back is puzzling!

[zinger5]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Looks like leftover flux from the factory soldering... but then it's also odd that this would be the only spot to have it while the rest of the board looks pretty clean.

Try cleaning it with some IPA and see if that changes anything. Probably not, but you never know.

Well, that turned out to be a very good shout - a rub down with some IPA to clean up those points on the rear of the board and it's powered up and working perfectly!

I don't know whether to investigate further what might have caused the issue or just count myself lucky it wasn't anything more serious and keep my fingers crossed it doesn't happen again!

Now to investigate its slow starting pair to see if the caps there are indeed on their way out.

Thanks again for everyone's help, particularly Per Hansson and Momaka!

Joe

[kaboom]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

A quick way to test a device that you suspect has dead or dying caps is to blow some hot air on the PCB with a hair dryer until everything gets fairly warm (but not so hot that you can't touch it.) If it works normally right away afterwards, there is a high chance capacitors are the issue. Of course, in some cases, it could also be bad/cold solder joints too. However, these are usually a little less responsive to heat changes and more to vibration / movement of the device.

Yes.


And most likely, after warming up, the unit will come right back on after power-cycling, not requiring a "warm up period."

I'd also suspect "small" caps, like C35 & similar.