Repairing Alesis M1 Active mk2 Monitor Speakers

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Been a while since I last looked at the schematics on these...

But with Q1 being the main switching MOSFET... if you have fluctuating voltage between pin 5 (primary ground) and pin 7 (UC3844 VCC voltage), then that means the UC3844 is likely OK and trying to start up. It also suggests Q3 and Q4 might be OK too. However, Q1 may or may not be good. One way to know is to measure the resistance of R15 (0.22 Ohms). You should get a very low resistance on your multimeter - same as if you were to short the probes together (i.e. lowest resistance your multimeter can measure.) If R15 is good, then Q1 is probably OK too and there is something else preventing the PSU from starting up. In that case, check diode D5 and resistor R5 (10 Ohm). These supply the UC3844 with power when the PSU is in steady-state operational mode.

If D5 and R5 are OK, check the output rectifiers on the secondary side, D10 through D13, along with the filter electrolytic capacitors, C17 through C24. If these are good, see if the PSU runs when disconnected from the amplifier board (measure voltage output across C18, C20, C22 and C24.) For t his test, it might be a good idea to connect a 100-300 Watt halogen bulb in series with the Live (240V AC in your case) line on the input. This is to prevent damage to the PSU, should some component fail suddenly.

If no voltage on the output at C18, C20, C22, and C24, time to check more components on the primary side. Start with Q3, Q4, and Q5. But before that, make sure the primary caps, C6 and C7 are discharged. BE CAREFUL around these - a faulty primary could have these still charged close to 340V total, which can definitely hurt you if you touch the wrong parts or damage your multimeter. You can discharge these safely with a low-power device, such as a hot glue gun, soldering iron, or portable lamp. Just connect the plug from one of these across each cap, and that should discharge the caps pretty gracefully. Once C6 and C7 are discharged, then check Q3, Q4, and Q5.
Q4 is a PNP transistor. With black MM probe on its Base terminal, you should get around 600 mV reading on your MM when you touch either the Emitter or Collector terminals with your red probe. For Q3, you should get the same readings, but just repeat the test with the red and black probes reversed compared to Q4 (since Q3 is an NPN transistor.)
Q5 may be a bit tricky. Due to transformer T2A, you'll probably see a short-circuit / very low resistance / 0 mV reading between Base and Emitter terminals. But for Base and Collector terminals, measure it like Q4 and you should get around 600 mV again, if I'm not mistaken.

[zinger5]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Wow, thank you both so much for your time and help! I'll work my way through those tests in the morning and will come back with an update on how it goes.

Thanks again,
Joe

[zinger5]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok, so here are the results of the first tests you both recommended - firstly R15 measured 0.2 Ohms on my MM so I think that is in range? R5 gave me a solid 10 Ohms and the diode D5 read 0.653 in diode mode.

As all of those sounded like they were probably in the right ballpark I moved on to testing D10-D13 - all of them read 0.468/0.469 on diode mode. Caps C17-C24 I tested in resistance metering mode and all gave the same figures - started at 0.2 Ohms and slowly climbed as the caps charged.

I should say that currently all of those tests were conducted with the components in circuit, is that sufficient at this stage?

Now I ready to start testing the voltage across C18, C20, C22 and C24 but I wanted to sense check your message about the light bulb in series with the live. Am I correct in assuming I would simply wire that bulb in series along the live wire from the wall outlet to the IEC kettle plug input on the speaker? I've got some spare 3-core so I presume making an extension with a bulb holder along it would do the trick for this?
Finally, in order to reach the rear of the board I'll need to take it off the housing but I presume I'll need to bridge the jumpers that run to the switch to run the board that way? Any recommendations on a clean way to do that or would a test lead with alligator clips on either end be the way to go?

Thanks again,
Joe

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok, so here are the results of the first tests you both recommended.
I should say that currently all of those tests were conducted with the components in circuit, is that sufficient at this stage?

Yes this all sounds fine, can you please take some good detailed high resolution pictures of the board for us to look at?
Perhaps we will notice something you missed because at this stage most things really seem fine...
You could just measure each and every component comparing them one-by-one on both sets and see if you find any differences...

Now I ready to start testing the voltage across C18, C20, C22 and C24 but I wanted to sense check your message about the light bulb in series with the live. Am I correct in assuming I would simply wire that bulb in series along the live wire from the wall outlet to the IEC kettle plug input on the speaker? I've got some spare 3-core so I presume making an extension with a bulb holder along it would do the trick for this?
Finally, in order to reach the rear of the board I'll need to take it off the housing but I presume I'll need to bridge the jumpers that run to the switch to run the board that way? Any recommendations on a clean way to do that or would a test lead with alligator clips on either end be the way to go?

Thanks again,
Joe

Yes this is correct, lamp in series with the live wire.
But another perfect spot for the lamp is across that missing switch (J3 on the schematic) you mention...
That said since you are already operating the set directly from mains and it has not exploded it is technically not necessary.
It is more when testing a set after having found some blown components and replacing them...
That said it is a very good protection against accidental probe slips...

[zinger5]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Sorry for the delay - I didn't have much time today but I've managed to take some photos of the components on the board in the hope that might give you some clues at to what the issue might be. 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?

I'm aiming to test the voltages across those secondary caps and, if needed, the primary ones momaka mentioned tomorrow, but let me know if you spot anything else on the pictures or need any others of specific areas of the board?

Oh, one other thing I keep forgetting to mention - my "good" speaker was the one I was originally more concerned about as it had been taking longer and longer to come on after I flicked the power switch. It now takes around 90 seconds to power up and for the blue led to come on. As they were bought as a pair I assume any age related degradation of components might be similar across both speakers, but does that sound like a capacitor on it's way out which might need replacing? Or might something else cause that long wait to power up after the switch is thrown? I've not yet touched that one since the other one stopped working but thought I should mention it in case it offers insight into the issue with the other one.

Thanks, Joe

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I should say that currently all of those tests were conducted with the components in circuit, is that sufficient at this stage?

Yes.
If you/we see something that we think looks odd, then that's when you might have to remove something to test it. Once done checking everything and if nothing pops up, then it might be time to start pulling components and checking out of circuit.

Finally, in order to reach the rear of the board I'll need to take it off the housing but I presume I'll need to bridge the jumpers that run to the switch to run the board that way? Any recommendations on a clean way to do that or would a test lead with alligator clips on either end be the way to go?

Yup, alligator clips will work for that. Or even better, as Per suggested, connect the series bulb there.

Yes this is correct, lamp in series with the live wire.
But another perfect spot for the lamp is across that missing switch (J3 on the schematic) you mention...
That said since you are already operating the set directly from mains and it has not exploded it is technically not necessary.
It is more when testing a set after having found some blown components and replacing them...
That said it is a very good protection against accidental probe slips...

Which is why I still do it myself, even though I've never had any accidents with that before. However, I did have improper wiring accidents, and the bulb did save me there are few times. Hence why I still think it's worth doing.

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.

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

I'm aiming to test the voltages across those secondary caps and, if needed, the primary ones momaka mentioned tomorrow, but let me know if you spot anything else on the pictures or need any others of specific areas of the board?

R27 (100 Ohms) on the secondary side looks like it ran a bit hot. Probably OK, but check it anyways.

R3 and R4 (both 47 KOhms) also look like they ran hot before. Worth checking those too. But again, make sure the primary caps are discharged (less than 1-2V) before doing that. Otherwise, you may damage your meter.

Finally, the new cap you soldered for C8, while not a problem for the time being (for testing), you may want to re-solder it as close to the PCB as possible once you fix the PSU. Vibrations from the speakers can cause joints to crack over time. (Hence why some components are glued down.)

Speaking of glue, I do see a bit of the problematic tan glue on the primary side of your PSU. But it doesn't seem to have turned dark brown so it's unlikely to be the cause of the issue. Otherwise, this glue is quite often a problem in electronics, particularly in places where things run hot. The heat bakes it into a dark brown color and then it picks up moisture from the air and becomes slightly conductive (in the high-KOhm to low MOhms range, which isn't a lot but could still disrupt some circuits.) So at this point, you can just leave it as-is. But once the PSU is fixed, you may want to remove it from components leads and exposed metal parts.

Oh, one other thing I keep forgetting to mention - my "good" speaker was the one I was originally more concerned about as it had been taking longer and longer to come on after I flicked the power switch. It now takes around 90 seconds to power up and for the blue led to come on. As they were bought as a pair I assume any age related degradation of components might be similar across both speakers, but does that sound like a capacitor on it's way out which might need replacing?

Yes, the slow start-up definitely does sound like a capacitor issue.
As electrolytic capacitors heat up, their electrolyte becomes more reactive, making the capacitors' ESR become lower.

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.

[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.

[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

[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!

[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??

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Here are the pics that I forgot...

[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.

[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

[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

[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

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...

[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

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

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.

[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.