Repairing Alesis M1 Active mk2 Monitor Speakers

[firespace]

Hi,

(This is my first ever post on badcaps.net, (looks like a great place by the way) so please be gentle with me as i have very little real world experience practical or otherwise mending electronics, I know very little about capacitor ratings or the contextual meaning of these ratings within circuits).

I have a pair of Alesis M1 Active mk2 Monitor Speakers, they are wonderful, however recently one of them has developed a fault. When the monitor is switched on the blue LED power indicator simply flashes and there is no sound from the drivers when audio is sent to the monitor.

Fortunately I have been able to track down what I believe to be the cause of this common fault (although sadly Alesis won't acknowledge the issue) with a few trusty interweb searches.

Here is what I have found so far-

This first link is a blog entry "Keith's Electronics Blog" is about an apparently similar or possibly identical issue, and gives a brief explanation on how he fixed it, as well as extremely useful comments on other peoples observations and issues they have encountered with these speakers, and the suggested fix. (I also posted one under the name BlueBlink if anyone can answer it)

http://www.neufeld.newton.ks.us/elec...#comment-26043

This second link was where Keith obtained his information on the suggested issues and fixes and can be found in the blog posting but I have included it here to save people looking.

http://studio-central.com/phpbb/view...t=554&start=17

What I have learnt from reading ALL the comments both on the blog and the studio-central posting is that essentially Alesis asked another company to build the PSU section of the monitors amplifier board which resulted in a poor design-

The power supply, apparently, was designed by a different engineering group from that of the rest of the speaker. Their mission was to cut the cost, weight, and size of Alesis power supplies by designing switching power supplies to replace the traditional analog ones. The M1 Active Mk II contains one of the first switching power supplies designed by this team – and, as we all now know, they didn't quite get it right. The power supply is sensitive to spikes in the AC voltage and slowly cooks itself to death.
(Thanks to -Obscuro for the information)

The upshot of all this is, that amongst other issues people have encountered, the main problem seems to be 2 poorly placed capacitors dry up and fail, these being C8 and C35 (see the pictures of the circuit board on the blog link I included).

Since I don't have a ESR tester and C8 and C35 capacitors seem to present the most common problem people have experienced, I would like to try to fix this first.
However to add to the complication Alesis or the PSU manufactures weren't consistent when installing these capacitors and it seem at least two types were used for C8.
220µf 35 V and a 330µf 35 V.

In my monitor C8 and C35 capacitors are the following-
C8- JunFu WJ105 ºC 0304 220µf 35 V green coloured cap
C35- JunFu HK105 ºC 0306 1µf 50 V navy blue coloured cap

I have subsequently discovered from your wonderful forum that JunFu or Jun Fu capacitors are 'bad caps' so my questions are these.

What is the absolute best capacitor to replace these with given their use in a high grade audio monitor and tendency to dry up because of poor placement?

Should I use the same rating capacitors, or would another rating fix the issues better?

Should the capacitor be polarised or non-polerized?
(I'm guessing non as apparently it's apparently AC voltage but I'm really just working with others information as i know so little).

I am considering soldering C8 in on the back of the board to avoid the heat, but as you can see there isn't much room, ideally I would like a replacement component that is the best quality possible, can handle the heat and permanently fix this problem and stop it ever reoccurring.

So far I have found these-
http://cgi.ebay.co.uk/Elna-Cerafine-...#ht_500wt_1154

Will they work? Are they any good?

Can anyone suggest the best cap for the job? Or any other helpful advice?

P.S - Here are some pictures of my units board so you can see for yourself.

http://www.flickr.com/photos/1229014...7624827549078/

Kind Regards,

Joe.

[Wrog]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hopefully some audio experts will chime in shortly... but in the meantime, I have some advice. I would personally use the same values to start with, and consider changing ALL caps (if one/two have failed, the others may not be far behind). After all, if you are fixing this to keep it for the long term, you may as well prevent future failure for a couple quid more while you're in there. I would recommend avoiding eBay, there are too few reliable places to get the caps you want. Most in the UK choose Digikey, Farnell or Radio Spares as their supplier. Only one of them has cheap shipping (for low volume), but I forget which (sorry!). Good luck and keep us updated!

[Th3_uN1Qu3]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

"Audiophile" caps are quite sensitive. I certainly wouldn't use them in a switching power supply. Use regular, low ESR caps. Brands like Panasonic, Sanyo (OSCON), Nichicon or Samxon are going to be just fine.

[stj]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

c35 is probably a "startup cap" so i'd use rubycon YXF or similar.
50v or 63v will be fine.

the other cap i'd probably also use YXF from the foto.
330uf will work better than 220uf - they probably either dropped it to 220 to save money, or raised it to 330 to improve performance.
higher is better for smoothing though.

the ones that effect audio will be the ones grouped around the heatsink on the end.
if they have to go then i'd use panasonic FK series - these are designed for long life in psu output stages.

[firespace]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok so it's looking allot like I should recap the whole board on both monitors, at which point it might also be worth recapping the crossover board as well since that uses Jun Fu caps too, and doing so can only improve the reliability and sound quality.

Although if some kind person were prepared to give me the exact order numbers from a good UK supplier for all the correct replacement capacitors I could probably undertake such a project myself, (if someone would offer to do this for me, I would happily catalogue all the caps used on the amp and crossover and post a full list here, just let me know) I can't help feeling that given the cost of the Monitors about £250, I might be better off sending both Amps and crossovers to someone with more expertise than myself.

Could anyone suggest a good recapping service who could undertake such a job that won't cost the earth?

Or let me know if they are prepared to suggest a full replacement list for me if I post up a full catalogue of the ones on the boards.

Thank you, Wrog, Th3_uN1Qu3, and stj for your advice and suggestions so far.

stj, please forgive my ignorance if this question is stupid, but could increasing the capacitance value for components potentially damage any other components further down stream? I really don't understand much about how this value effects things.


Much thanks,

Joe.

[Wrog]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Or let me know if they are prepared to suggest a full replacement list for me if I post up a full catalogue of the ones on the boards.

This is your best bet... info to include for each cap would be reference designator (to help folks in the future), capacitance, voltage, series (usually two or three characters printed on the cap), diameter and height. I'm afraid I wouldn't be of any help (little audio knowledge and don't want to steer you wrong) but hopefully someone will chime in again.

[stj]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

make a list of the caps including the diameter - this is important.
the best place in the u.k. is farnell

as for sending them to someone, postage on speakers will be a bitch!

[PowerAmpFreak]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I once did a repair to this monitor smps. Replacing C8 fixed the problem. It didn't start up at all before.

[firespace]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok so a whole lot of squinting with a flash light later here are all the caps (with details) for both boards on the active electronics of 1 monitor.


On the power supply board-

2x JunFu - Width 22mm Hight 35mm Dark Blue
390 uF
200V
HK105˚C
0304

2x Su'scon - Width 13mm Hight 20mm Brown
390 uF
50V
SD105˚C
0319 (V)


5x JunFu - Width 8mm Hight 19mm Green
220 uF
35 V
WG105˚C
0304


2x JunFu - Width 8mm Hight 16mm Dark Blue
82 uF
63 V
WG105˚C
0304


1x JunFu - Width 5mm Hight 11mm Dark Blue
1 uF
50 V
HK105˚C
0306



On the amplifier board-

3x JunFu - Width 8mm Hight 12mm Black
100 uF
50 V
RB85˚C
0304


2x JunFu - Width 8mm Hight 12mm Black
100 uF
50 V
RB85˚C
0301


8x JunFu - Width 8mm Hight 11mm Black
10 uF
63 V
RM85˚C
0304

Thanks for all the help so far, I hope some kind expert can give me a full list of order numbers for new capacitors that are better replacements, and a short equipment list of all the tools I shall need to do a good job would be very much appreciated.

The main issue with these Monitors seems to be the power supply section has a few of the green caps that dry up because of a board design error that places one of them too close to a resistor (see the photos in my first post), so perhaps some improved capacitors with the same capacitance but higher ˚C rating might be wise for those green caps?

I have included exactly what is written on the caps, and given dimensions and even colour too for what it's worth.

I don't think I left anything out but it was tuff reading all the details due to the angle some capacitors were soldered on at.
But if any details are missing or look way out of whack please let me know and I will triple check it.

Much thanks,

Joe.

[firespace]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Bump -

If someone could make a replacement list from a good UK supplier for me I would be extremely appreciative, I would simply do it myself, however I am a novice at electronics although I have good soldering skills and can do the repair, choosing the correct components and tools to do the job well is beyond my limited knowledge.

I throw my predicament at the forums mercy.
Would anyone provide a supplier, item list, component order number, and price for the components required?

-J

[toastygoodness]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

mine just failed. is it possible to use a poly cap in an monitor p/s? or do i have to stick to a regular low-esr lytic rubycon? or even general purpose?

[Th3_uN1Qu3]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Just use a regular low-esr electro.

[toastygoodness]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Just use a regular low-esr electro.

alrighty, thanks!

[LuigiDJ]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hello everyone. My father gave me this Alesis M1 Monitor to fix, but when I opened it, I found some traces blown. Now I don't know where they go. With the photos posted by firespace, i could figure out the top traces and the value of the blown resistor (470 ohms), but I don't know where the bottom traces go. I'd like to fix this monitor just for the fun of hearing it a couple of weeks. Does someone have a photo of the bottom part of the power supply?
Parts checked bad: 2 diodes, 2 mosfets, 1 resistor, 2 capacitors, 2 main capacitors (don't know for sure), 3 main rectifier diodes, 1 fuse...... and still counting. Those parts will get replaced, and I hope to get it back to life.
Thank you.

[lmcancu]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Did you try cleaining it? Maybe parts of the traces are still there under the "dirt"?

[LuigiDJ]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Did you try cleaining it? Maybe parts of the traces are still there under the "dirt"?

No, unfortunately there's no sign of the tracks, just the bare fiberglass of the pcb.

There seems to be another M1 where this came from, I'll go check and see if I can get a photo of the smps.

Thanks

[momaka]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

PCB looks pretty bad. Make sure to give it a good cleaning before putting any new parts.

And if you can't fix it, perhaps you can wire an external PSU with the same voltages. I always find that as an easier alternative, even though it looks bad most of the time.

[LuigiDJ]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I fixed it!
These are the photos of the repair, not so beautiful, but it's working.
Very nice sound, wish I could keep it...
How much can I bill for this kind of repair?
I replaced 4 x 1n4007 diodes, 2 x 1n4148, 2 irf840, 1 x 470 ohms, 1 x 330uF, 1 x 1uF, 2 x 390uF and the UC3842 ic.

Thanks.

[Th3_uN1Qu3]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

So by your description pretty much the whole supply was toast. This is called bad design in my book.

[LuigiDJ]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

So by your description pretty much the whole supply was toast. This is called bad design in my book.

Yes, it seems to be a bad design, the 330uF cap is very close to a power resistor, that heats it and dries the cap, leading in my case to the explosion of the cap, and in a chain reaction, took with it all those parts.
In the repair, I left the new cap with long pins, over the power resistor, hoping it don't heats so much. I was hoping to put it under the pcb, but there's no space.