Repairing Alesis M1 Active mk2 Monitor Speakers

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

R5 = 10ohm in series with the aux supply primary winding?
D15 = BAV21 that's connected to pin one of U1?

Why exactly are you replacing those?

And do you have (or have you ordered) a replacement for the 0.22ohm R15?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I will replace only what it`s bad. But all cost 15E and i order them just in case (anyway i will check C8 on the good one and i will change the place of C8)...
Sorry, not R5, D15, i order R15 and D5.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

So D5 was bad too?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

The esr metter has arrived.
R3, R4 - 38k
R15 -0.25k
C7 - 380, C8 - 390
C16 - 650nf (on schematics it`s write 160V, but on the C16 it`s written 100V)
The parts tomorow.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

R15 - 0.25ohm

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I changed the U1 with UC3844N like u said and it`s working .
I took out the bad U1 and replaced with one dip8 socket.
I changed the C8 and C35 in the good one and i moved the C8 on the other side of the board (both).
Thanks !!!

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

"Hate to say i told you so, but... i told you so"

Either way, congrats!

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I let them "working" on moderate volume and after 30 minutes the bed one started to make some sounds like an echo . Only for 10 sec but repeted. I have changed the dac, the whires.
Any ideas?

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

"Some sounds like an echo" is a bit vague - some words can mean very different things to different people.

I don't suppose you can somehow record the noise, can you?

Or what if you have no input signal connected? Does it still make that noise?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I will record the noise. He made the same noise with no signal and with volume(gain) to minimum. Strange after 4 hours the M1 works fine with no noise.
I will let them (both) without the power cord tonight .

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

When i disassembled the speaker, i disassembled and the part with the inputs.
And i discovered that, when i push that part (on the bass/mid....switchs) the speaker make that noise. So i must take out the board with the inputs and to check what i did wrong.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I've had a similar issue (lousy signal switches) on my Tannoy Precision 6D's once or twice...

[CasbienBarr]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

OK,
Sorry for the delay, finally got some time to work on the board, everything apart from the C6 cap seemed fine. But I'm replacing the caps and R3 and R4.
Parts should come tomorrow or the day after, I'll post how it goes.

Anyone know what gauge wire I should use the replace the burnt out trace from C6 to R3?

[dannykap]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all and thanks to those who have contributed to this thread. I recently acquired for free a pair of Alesis 620 active speakers. Neither of them would power up. On inspection, both had black burn marks on the board near r4 and the fuses were blown. I managed to get one working by replacing 2 diodes, the fuse c8 and r4. On switching on, the power light came on blue as expected. However the sound from the speaker was terrible. The woofer wasn't working. I put the board in the other speaker cabinet and rechecked the connections, with the same result. I already had one working speaker (bought used for £5! ) so I exchanged the amp circuit boards with the power supply that I want able to repair. On turning on, the red light came and the speaker emitted a loud high pitched noise. I opened it up again and tightened all the connections and this time when I switched on, the red light comes on, but the speaker works perfectly! I'm happy that I have ended up with two working speakers for a total of £5, a little petrol money to collect them and a few pence in spare parts, but the red light does worry me a little. I understand that it should come on only if the input is clipping. It definitely isn't and the speaker sounds great and apart from the light seems to be working perfectly. Can anyone advise on how to get rid of the red light? Also, in case I manage to fix the second power supply (bit more tricky and am not yet sure what is wrong), what could be wrong with the amp board that it isn't driving the woofer?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hy all.Unfortunately the fuse blew again. I will disassamble the speaker again.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I mesured all the FETs and all the diods. All good. I change the U1 with the UC3842 and work again. Luck me, i ordered one 3844 and one 3842. Why the U1 died?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

On the schematic the fuse F1 have 10A, on the board it`s write 5A and i put 5A fuse.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Any ideea?

[Micwest]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Okay, here another alesis (try to) repear story
I'm a newby here, read this hole post(which helps me already a lot!), some other sites and videos around repearing, I'm able to solder, know how to use a ohm and volt meter, but don,t have much knowledge of electronica. But I hope some masters can help/tip me to solve my issues.

I bought 2 defect M1 620's which burn out fuse directly when powering on. The pcb/print of these have number 9-40-B601-E, which is also in the service manual of MKII(N8), so I guess this should be the same?

One speaker has no visible damage, only replaced once the known C8 (still close to the hot R3/4) and C35, but don't know if this ever worked. I would like to start with replacing D1-4 and maybe C1-2, and order at least also uc3842, with foot..

The other has burned places, like R11, D5, R5 and one burnedout line on the PCB(between +C8 and port7 of UC3844 and Q3, I think caused by blown R11 ), see in red in picture of scheme, Also from Q3 a part was broken off. In the picture of the scheme you see in red all parts which have visual damage, or easy to measure when on the pcb. In some cases I wrote what I found on pcb(other type/value)
I was thinking about replacing at least al red marked parts and the yellow marked parts.

But I still don't have a clue which could have cause this issues, do I have to replace more? Is the a chance all replaced parts will burn out again? Can/need I measure some more part? In- our outside the pcb? Should UC3844(conform scheme, in my case uc3842) be replaced? Could damage Q3 kill Q4/Q1?
Some people have to exchange C1&2 together with D1-4, is the smart to do/order anyway?
I can easy solder R3+4 on the back of the pcb for heatproblem, like R15, see picture. (I guess pcb in the 620 are mounted the other way as mkII? )
They will maybe touch the glass wool, maybe I have to cut away? I guess it won't burn? And solve the heating problem?
I'm not in a hurry, just a nice little project. I still have to order all parts.
Well, I hope someone can help me a little :-)
Thanks,
Michiel

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Step one - remove the visibly damaged components
Step two - remove all of that crap brown (or black) glue; it dries out, it's corrosive and it turns conductive

R11's the really-blown-up one in the middle of the third photo, right? In that case, there's a good chance the 3842's blown as well.

Do you have a diode-test mode on your multimeter? That would / will come in really handy for double-checking some of the silicon components there.