Repairing Alesis M1 Active mk2 Monitor Speakers

[DarthBoz12]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Thanks for that. There is about 3/8" on 3 of the leads that has broken off. I have some magnet wire on order and plan on re-wrapping the whole thing.

Once I get that done, I can go back to the other stuff. I have gone through the whole thread and it is quite informative. I plan on relocating C8 to the C14 position. So far I have been pretty lucky compared to others as mine is not blowing fuses and hasn't obviously blown out any components.

[vshitikov]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi, guys. Great thread.
Just purchased a set of broken speakers here in France in a hope to repair them. I'm electronic engineer so it should be doable, but while reading this thread I started having serous doubts if this is a reliable solution. The initial design is quite poor and unreliable. I think batches of capacitors were faulty when Alesis first built them but the rootcause of all is a poor thermal management. That's why everything blows in a semi-random manner. Do you think that by recapping the speaker with decent capacitors and replacing faulty components will bring speaker to a long life? Or it is a matter of time when it will blow again? I'm worried as it might catch fire or something as I often leave speakers unattended? Do you heave return of experience of a lifetime with the recapped units?
Thank you all for this work.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I've recapped* two pairs of these Alesis monitors, years ago (whenever i posted here about them), and later sold them off to two different friends, and i've yet to hear any complaints about either pair, so...

* Recapped = using Japanese electrolytics, plus moving that Vcc capacitor from next to the heatsink, to next to the UC384x, and moved the ceramic cap to underneith the chip

[vshitikov]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I've recapped* two pairs of these Alesis monitors, years ago (whenever i posted here about them), and later sold them off to two different friends, and i've yet to hear any complaints about either pair, so...

* Recapped = using Japanese electrolytics, plus moving that Vcc capacitor from next to the heatsink, to next to the UC384x, and moved the ceramic cap to underneith the chip

Thank you for your reply. I continue width the project. Changed the caps with the nippon chemi-con, now will change some transistors and maybe PWM circuit as I have no means to test it reliably and every time I power up the speaker with at least on burned component it burns something else. I also discovered that my 5A fuse not only fuses but explodes

[thafx]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all, this is my 5th attempt to resurrect this speaker

Ive just replaced

r5,r11,r15,r16,r18 -
d1,d2,d3,d4,d5,d6,d7,d9,d14,d15,d16, -
q1,q2,q3,q4,q5,q6,q7 -
c1, c2, c6, c7, c8, c35, -
rt1 -
f1 -
u1 (TL3842P) + dip8 socket -

after all this,plugged in and switched on, no sign of power, dead, no fuse pop, nothing. all solder joints have been checked...

does anyone have any advice at this stage ?

cheers

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I don't suppose you've taken any voltage measurements anywhere, have you?

[thafx]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I don't suppose you've taken any voltage measurements anywhere, have you?

Hi Khron , thank you for your time & excuse my blunt post.

I do have a Multimeter, everything replaced is new & was checked to its specification.

After going through this thread multiple times (similar situation to markovitch's & Shabazxz's posts)

Im suspecting the odd TL3842P chip to be the suspect, (I ordered UC8342N but received this IC)

The IC readings :

GM3842 / PIN7=127 / PIN8=565
TL3842 / PIN7=413 / PIN8=430


New UC8344AN + UC8342N IC's have been Ordered.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Are those reading supposed to be in mV, on the voltage measurement range, or....?

[thafx]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Are those reading supposed to be in mV, on the voltage measurement range, or....?

Well, for starters, with the power off, assuming your meter has a diode-check mode, that could be a start.

Red probe on pin 5 of the chip (careful how you count them), keep it there, and black probe first on pin 7 (Vcc), and then pin 8 (Vref). Normally, you'd expect something around a diode voltage drop (5-600mV or so); anything less, and the chip may well be toast.

Following the Instructions here

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok. Are those readings with the chip on the board, or off it?

And by voltage measurements, i meant checking, for example, that you have about 320V DC across C6 and C7 (in total, since they're in series), and whatever supply voltage the PWM chip has (between pins 7 and 5).

[e_poirier2004]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Trying to repair Alesis M1 620. Replaced C6, C7, C8, C35, R3 and R4 and no reaction from supply. The fuse is not blowing, I have 320V between C6 and C7. Power on U1 is 10v between pins 5 and 7 and 1.9v between 5 and 8. I desoldered and tested all the transistors and they seem ok. Diodes also check good in circuit. Looks like U1 doesn't oscillate. Also checked R15, RT1 and RT2 after desoldering and checked ok. I checked U1 and I see a diode between 5 and 7 & 5 and 8. At this point I suspect U1. C8 replaced by a chemicon 330uF 125 deg gen purpose. ESR is low on my meter. The other speaker from the pair restarted with the same capacitor. What do you think ?

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Well, 3842 are cheap as chips, so i'd replace that too. Can't hurt to have a known-good PWM controller, anyway.

[e_poirier2004]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Thank you Khron. Will order some from Mouser. I also found a low ESR cap for C8 that is 135 deg. I already installed a socket for U1. It just didn't made sense. Everything looks good. I desoldered Q1 to Q7 and tested them one by one. Everything seems ok but the chip wouldn't start. I'll replace the chip first and get back to you. Might take a while to get the chips due to holiday season.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

C8 doesn't necessarily need to be uber-high-temp, as long as it's not right up against a hot heatsink. I guess my relocation trick worked well enough even with "normal" 105C low-ESR caps, since neither of the two friends i sold a pair each to, has yet to complain of any failures, and it's been about 7 (seven!!!) years since then.

[e_poirier2004]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

After replacing U1 (U2 and U3 for good measure...) the monitor is operational !!!! Thank you for the infos !!! Great thread on those monitor.

[thafx]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok. Are those readings with the chip on the board, or off it?

And by voltage measurements, i meant checking, for example, that you have about 320V DC across C6 and C7 (in total, since they're in series), and whatever supply voltage the PWM chiphas (between pins 7 and 5).

Hi again and Happy New Year,

Those are readings with the chips off the board

I have traced 240v voltage from the power socket through the circuit upto C6/C7 which does not give a DC voltage reading.
I've removed & tested the New caps on the Ohm meter, they're reading slowly toward infinity. there is no supply voltage on U1 pin5-7 when powered

I have also moved c8 to c14 (c14 attached at the back), replaced U3-TL431 and tested UC3842N, UC8344AN with similar diode voltage drop readings (off the board) as before

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

If you're getting NO voltage across C6 and C7... Is the fuse, by any chance, blown? And/or the mains power switch?

[thafx]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

If you're getting NO voltage across C6 and C7... Is the fuse, by any chance, blown? And/or the mains power switch?

Hi again, I inspected the board and found a damaged trace between D2 to C6+. After repairing the trace, I now read 330V across C6 & C7

U1 PIN5->PIN7 reads just under 10v with UC3842N & UC8344AN
PIN5->PIN8 reads less than 1V ( main suspect now )

I have also replaced U2 with a DIP6 socket with a new TCDT1124 chip with no change.

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi Guys,

i have two failed MK2 here. I was able to repair the first one (390uF caps and the 1N4007 diodes). But now im failing with the second one. Its just dead.

Im not an expert so I guess i need help.

I have already replaced C6, C7 (390uF caps), the 1N4007 diodes, C8 and the 1uF cap.
Also i replaced both the IRF840 (Q1 + Q2) and the 10 ohm NTC.

Its not switching on, no LED at all.

Can someone give me a clue what to do next? Does it make sense to replace the UC3844N?

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Can someone give me a clue what to do next? Does it make sense to replace the UC3844N?

Yes, it does.