Repairing Alesis M1 Active mk2 Monitor Speakers

[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.

[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

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...

[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

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

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

No worries, we aren't going anywhere.


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


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.


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.


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


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



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

Well, before I get into testing diodes and such, is the board toast? As you can see, there's nothing remaining of the two holes for L4 and D14.

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well, before I get into testing diodes and such, is the board toast? As you can see, there’s nothing remaining of the two holes for L4 and D14.

Well, your board is toast in the literal meaning.

But it's not "done for" type of "toast".

Just keep drilling / grinding to get rid of as much charred PCB as possible. Yes, there will be a big hole in the board afterwards, but that's not an issue. You will just have to use some jumper wire to connect components to their proper traces and/or other components... and probably glue some of them down afterwards to make sure nothing moves away.

I've seen boards much worse on here get repaired. Namely, this Delta DPS-340CB ATX power supply:
https://www.badcaps.net/forum/showthread.php?t=9660

Here are the pictures direct-linked if you don't feel like reading through that thread:
https://www.badcaps.net/forum/attach...6&d=1273364750
https://www.badcaps.net/forum/attach...8&d=1273364750
https://www.badcaps.net/forum/attach...0&d=1273364750
https://www.badcaps.net/forum/attach...7&d=1273978870
https://www.badcaps.net/forum/attach...9&d=1274834154
https://www.badcaps.net/forum/attach...2&d=1275187900
https://www.badcaps.net/forum/attach...4&d=1275187900

^In case of the above ATX PSU, everell did replace the missing/burned PCB parts... but for that one, it was probably necessary to attach all of the components. Your board has just holes for 2-3 parts that were affected. So no need to fill-in the hole with anything. Just solder the components the way they should be as if the PCB was there, and then connect the floating ends/leads with jumper/copper wire to other traces where they need to connect to.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well, your board is toast in the literal meaning.

But it's not "done for" type of "toast".

Just keep drilling / grinding to get rid of as much charred PCB as possible. Yes, there will be a big hole in the board afterwards, but that's not an issue. You will just have to use some jumper wire to connect components to their proper traces and/or other components... and probably glue some of them down afterwards to make sure nothing moves away.

I've seen boards much worse on here get repaired. Namely, this Delta DPS-340CB ATX power supply:
https://www.badcaps.net/forum/showthread.php?t=9660

Here are the pictures direct-linked if you don't feel like reading through that thread:
https://www.badcaps.net/forum/attach...6&d=1273364750
https://www.badcaps.net/forum/attach...8&d=1273364750
https://www.badcaps.net/forum/attach...0&d=1273364750
https://www.badcaps.net/forum/attach...7&d=1273978870
https://www.badcaps.net/forum/attach...9&d=1274834154
https://www.badcaps.net/forum/attach...2&d=1275187900
https://www.badcaps.net/forum/attach...4&d=1275187900

^In case of the above ATX PSU, everell did replace the missing/burned PCB parts... but for that one, it was probably necessary to attach all of the components. Your board has just holes for 2-3 parts that were affected. So no need to fill-in the hole with anything. Just solder the components the way they should be as if the PCB was there, and then connect the floating ends/leads with jumper/copper wire to other traces where they need to connect to.

Alright. I understand about running jumpers to connect the component to its proper trace... It looks like in this instance I can just solder one of each components' legs to those little bare sections (outlined in red) on the edge of the hole?

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yes exactly, just before you test the unit take a good photo of your work so we can confirm no mistakes have been made.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yes exactly, just before you test the unit take a good photo of your work so we can confirm no mistakes have been made.

Welp... it sure ain't pretty... It really felt like the holes were too big for the solder to pool at the bottom of the lead on C8.

I hope L4 and D14 look alright?

John

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well it wont win any beauty contests and I would not run it long term with the cap on those long legs!
But it should be enough for testing, I do recommend to have an incandescent light bulb in series with the live or neutral to limit the current if there are any shorts.
Did you measure the diodes on the multimeter to make sure they are ok when you had them out?

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well it wont win any beauty contests and I would not run it long term with the cap on those long legs!
But it should be enough for testing, I do recommend to have an incandescent light bulb in series with the live or neutral to limit the current if there are any shorts.
Did you measure the diodes on the multimeter to make sure they are ok when you had them out?

+1

Also, if the PSU does end up working, it would be a good idea to replace that Jackcon capacitor with something better for the long run. These aren't known for their reliability... and really that applies to just about every non-Japanese brand. Should have gotten some Rubycon, Panasonic, Nichicon, or United Chemicon caps while purchasing the inductor from Mouser. But for testing, it should be OK. I have a few of these Jackcons in my "test parts" bin as well... and they are OK sitting there. Definitely won't last in a stressful or hot PSU, though.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

+1

Also, if the PSU does end up working, it would be a good idea to replace that Jackcon capacitor with something better for the long run. These aren't known for their reliability... and really that applies to just about every non-Japanese brand. Should have gotten some Rubycon, Panasonic, Nichicon, or United Chemicon caps while purchasing the inductor from Mouser. But for testing, it should be OK. I have a few of these Jackcons in my "test parts" bin as well... and they are OK sitting there. Definitely won't last in a stressful or hot PSU, though.

Regarding C8 and its legs, I put it over there to get it away from the hot resistor. How do I get it away from the heat of that without having long legs?

Someone needs to show me what you mean about adding a light for testing. All I can see in my head is a standard household lightbulb attached to this thing somewhere.

Jackson capacitor??

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Regarding C8 and its legs, I put it over there to get it away from the hot resistor. How do I get it away from the heat of that without having long legs?

Reply in this quote:

Heat is not a problem in the set in general, only the stupid location of C8 is a problem.
Instead of a fan I would do what Khron recommends in some of his posts: basically swap physical locations with C8 & C14.
Apparently this is what Alesis did themselves in a later revision (F).
However Khron's mod is even better, because C14 will be too far away from the UC3844N to be useful in that physical location.
So he just solders it to the bottom of the chip instead, see these two posts:
https://www.badcaps.net/forum/showpo...0&postcount=27
https://www.badcaps.net/forum/showpo...&postcount=384

Someone needs to show me what you mean about adding a light for testing. All I can see in my head is a standard household lightbulb attached to this thing somewhere.

Here is an example: https://www.badcaps.net/forum/showpo...4&postcount=70

Jackson capacitor??

That's the manufacturer of capacitor C8 you put in there, a really "meh" brand (not even likely to outlive the original that was in there)...
There are only a few consistently reliable capacitor manufacturers in general: Rubycon, Nichicon, Sanyo (Suncon), United Chemi-Con (UCC), Panasonic
P.S: You should change C35 too.

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

*EDIT*
Sorry I'm "echo-ing" Per's post again.
By the time I type up my post and hit submit (and especially if there were other distractions around me), there's always another reply, lol.

Regarding C8 and its legs, I put it over there to get it away from the hot resistor. How do I get it away from the heat of that without having long legs?

You can raise it up to about 1/4" from the board and bend it away from the heatsink or hot resistors... or just place it elsewhere on the board (I believe this was mentioned in several places somewhere in the first few pages of this thread.) Otherwise, placing capacitors like this with very long leads makes them ineffective at high frequencies. The long leads raise the ESR and also act like little antennas, spewing electrical noise to other components and parts of the circuit. So generally, it's not a good practice in most applications.

Someone needs to show me what you mean about adding a light for testing. All I can see in my head is a standard household lightbulb attached to this thing somewhere.

This one was posted by Toasty a long time ago, but right to the point:


And same thing with more details:
https://www.badcaps.net/forum/showpo...4&postcount=70

Jackson capacitor??

Jackson, Jackcon... whatever. These are all goofy China brands. Look at the two photos you posted of C8. The replacement cap has "Jackcon" written on it, which is its brand.

[jgulyas]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well... mild success I guess... the unit powered on and the blue LED is no longer blinking... but now it's emitting simultaneous tones 13.5kHz and 6.3kHz.

Any ideas with that one??

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Not really but it might be worth a test to put back the original inductor instead of the new one you bought.

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well... mild success I guess... the unit powered on and the blue LED is no longer blinking... but now it's emitting simultaneous tones 13.5kHz and 6.3kHz.

Any ideas with that one??

Is the noise loud or faint? Also, is it coming from the speakers or the power supply itself? Any chance you could provide a quick audio recording?

Before anything else, perhaps double-check your setup. In particular, try taking your working speaker set and wire it up the exact same place and cables that you used with this one. Then repeat the test with this one. If the noise is persistently staying with this set, then perhaps we are not done yet with the repair.

Per mentioned a valid point - could indeed be something with the new inductor/toroid making the PSU oscillate and produce extra noise.

It could also be that perhaps the output caps on the PSU are failed or have started to fail.

Since you already have the old inductor, you can try swapping the new one with the old one. (And when you do, definitely make sure to use the dim bulb trick, just in case.) If the noise persists, then I would suggest doing a full recap on the unit with proper high-quality caps. There is also a small chance that perhaps when the PSU failed, it also damaged or partially damaged something in the audio / amp section of the speakers. But I think that would be a rare/unlikely case. On that note, do the speaker play audio OK, aside from the high-pitched noise(s)?

[Per Hansson]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

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.

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.

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