Repairing Alesis M1 Active mk2 Monitor Speakers

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I have the schematic.
On the bad board D10-409, D11-408, D12-410, D13-408

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

And OL if you reverse the probes?

Next, you could check the four diodes at the mains input (D1-4).

After that, also on the diode test mode, check the MOSFETs - red probe on source (right-most leg, as you look from the front of the FET) and black on drain (middle leg).

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

On reverse nothing (show 1)
D1 - 561, D2 561, D3 561, D4 562 (reverse nothing). They are new.
Q1 - 444
Q2 440

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hmm... Have you replaced the PWM chip as well (U1)? And what reading do you get (in ohms) if you measure R15 (the 0.22ohm at the source leg of Q1)?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

On both boards mesured on the board it`s show 1.1 (on the 200 scale).
I didn`t replaced the U1.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

1.1's a bit high. Can you read the colour-code that's on that resistor?

If the FETs are ok, and so is the rectifier bridge, i would begin to suspect U1. If it's stuck holding Q1 open (allowing current to flow through it), that could explain why the fuse blew the second time.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

red red silver gold.
i will change the U1. (next week)
And after how can i try the board?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

on the schematic the U1 is UC3844N, and on the board on the U1 it`s written 3842 and below5E02.
What it`s the correct IC?

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Red = 2, silver = divide by 100, gold last = 5% tolerance => 0.22ohm 5%. Waaaay out of spec (by about 4-500%). So you'll definitely want to replace that too, preferably with a non-inductive (ie. not wirewound) one.

http://www.hobby-hour.com/electronic...color_code.php

The best / easiest(?) way would be with a so-called "bulb tester", ie. an incandescent (old-school tungsten, NOT led or cfl) lighbulb in series with one of the two mains wires.
When you turn the DUT (device under test) on, it will flash briefly while the caps charge up. If it stays lit bright, there's high current draw, so something's wrong, but it will also limit the current so nothing should get damaged further.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

i will replace R15 on boath board. On the good one i will change the C8 .

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Change C8 and see if you can move it to where C14 is, next to the PWM chip (and thus, away from the hotspot it's in). I did that on my pair, back in the day, which i then sold to a local friend, and i haven't heard of any issues since then (must be 2-3 years since then).

https://www.badcaps.net/forum/showpo...0&postcount=27

Yup, autumn 2013

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

M1 620 it`s the 3 edition. Am the power board it`s reversed. So i can move the C8 on the back. I don`t understand why did they removed the power button.
There is no stand-by on these monitors and the only way to shut down it`s to remove the cord from the wall.
Please tell me what it`s the correct U1?
Thanks

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Schematic in the service manual says UC3844 (in DIP package), so that's what i'd go with.

I guess my first pair of M1's had a newer revision of the power supply (ie. not the board layout that's in the service manual), so C8 is no longer in the hotspot it was in the earlier revisions.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Alesis M1 620 is the M1 MK3. And the power supply it`s the same. But the U1 it`s other.
I don`t know witch it`s better.
3842 or 3844

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

In this application, either one will do. 3842 can go up to 100% duty cycle, the 3844 only to 50%.

At least in normal circumstances, it shouldn't need to (try to) go over 50%, even with a 3842, but since this is some funky "emulated" double-forward or half-bridge converter, it's probably safer to go with the 3844 (as per the schematic / board).

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hi all,

So far this thread has been a great help, thanks all!

So, after having not used my M1s for a while I turn them on and one gives out the most awful sound and I immediately turn them off. When I turn them on again there is a bang.
Opening it up its seems C6 had blown, taking with it the trace leading to R3. I removed it along with C7, R3, R4 and C16.
Through this thread I've discovered that my board is likely one of the revisions. The serial in the bottom right corner the PCB ends in F instead of E as shown in the service manual Khon kindly provide (Godsend), C8 and C14 have switched places and there are several other slightly variations which is what my questions are in part about.

First off, the pieces I removed:

C6 is blown and C7 looked cracked, they are also Fuh Yin caps so they will be replaced.
Would these be a good replacement? Or do you have a better suggestion? Anything with a long life maybe?

http://uk.farnell.com/rubycon/200kxw...rad/dp/2342082

When I removed R3 and R4 they tested 37.0k and 37.5k, however the components list in the manual lists them as 47k 2w 5%, but the bands as far as I can make out seem to be orange, yellow, orange, gold. When I check out that colour code though I get 34k, but it does says non-standard. So now I'm really confused? The schematic says 47k but that manual is for the E board not my F revision, and with them both measuring around 37k seems maybe they got bumped down, but with the bands coming out with 34k I'm unsure of what to do here.

C16 I think is fine but since its out I thought I'd just put a new one in but on the component list in the manual it is listed as 0.68uF 100v, on the schematic it says 160v and the actual component on my board says 250v.
So go with what is on the board? Something like this?

http://uk.farnell.com/vishay/bfc2468...rad/dp/1166123

This made me make a list of the differences between the schematic, the component list and my board as well has against my measurements and I found a few other variations. If these components turn out to need replacing, the ambiguity makes me unsure so any suggestions for replacements here
would help.

R5
In the components list is says 10ohm 1/8w 5% and 10ohm on the schematic, but mine has the colours Green, Brown, Gold which I get as 5.1ohm and I get a reading of 5.4ohm.

R20 & R23
The components list and the schematic both say 1.69kohm 1/8w 1%, however the colours are Brown, Violet, Black, Brown, Brown which I can only find as 1.7kohm 1% and the readings are 1.67 and 1.51kohm.

R18
Both list and schematic say 100ohm 1/4w 5% but the colours are Yellow, Violet, Brown, Gold which I get as 470ohm 5%.

R27 & R28
List and schematic claim 100ohms 1w 5% but the bands on mine say 2ohm and my reading on both was 2.4ohm.

C8
List and schematic say 220uF 35v but mine says 330uF 35v

Q3 & Q4
List and schematic claims that Q3 and Q6 are 2n4401. Q6 is but Q3 says 2n5551.
Q4, 5 and 7 are said to be 2n4403 but Q4 is 2n5401

U1
List and schematic say UC3844N but mine says GM3842.

I am a novice, I may be asking some stupid questions so feel free to correct my foolishness.
Any help you could give would be much appreciated.

Also the dreaded C8 is moved on my board but its still a Fuh Yin cap, should I change it out?
C35 is also a Fuh Yin as well as every other electrolytic. Get rid?

If anyone has or knows how I could get hold of a service manual for my revision of the board, if it even exists, It would answer a whole lot of these questions for me.

I have the same revision of the board (only the parts. C8 it`s near R4 on my pcb)
So i must change C8. Now i have 220 like in the schematic.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

And if i change the place between C8 and C14?

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Strange. On the good board it`s 330. On the bad one, C8 was changed (not by me. i recived like this. It was repaired once) with 220uf.
On my board R1,R2, C3,C4 is missing.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

And if i change the place between C8 and C14?

As you can read in my description (somewhere on page 1 or 2), i mounted the C8 (electrolytic) into where C14 is/was, and then soldered on C14 on the bottom of the board. You want C14 (the 100nF) as close to the chip (U1) as possible.

R1-2 and C3-4 aren't entirely necessary for the power supply to work, they're more for the safety / EMC side of things.

[Shabazxz]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Ok. I hope tomorow U1 will arrive. I request the UC3844N and UC3842N, FETs, R5, C8, Q3-7, D15 and one ESR meter. And one DIP8 socket. First i will check the components from the board and if some one it`s broke i will change it. If all are good, i will change the U1 (UC3842N like on the board) and after i will test with the bulb.
What power must be the bulb? 10,15,40..W?
Thanks!!