Repairing Alesis M1 Active mk2 Monitor Speakers

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Thank you, Im ordering some. Will let you know!

[Jehanne]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Thanks for all the great information posted here. It has helped me repair one of my Alesis M1 Active boxes. Still working on the other one. I have changed many components and now it seems that the U2 optocoupler is also damaged.
I have 3 questions :
1. A substitute 6 pin optocoupler has been recommended. It is a 6 pin AN25 as opposed to the original 6 pin TCDT1124. The specs are close but only 30v max. Collector to Emitter as opposed to 70v for the 1124. Should i go ahead with the substitute or try to track down a 1124?
2. I am waiting on the arrival of some .22 ohm carbon film resistors however I am wondering .... Is it ok to use a .22 ohm fusible resistor for R15?
3. My boxes are the original mk1s. Q3 and Q4 are are 2n5551 and 2n5401 is it ok to use 2n4401 and 2n4403 as show on the schematic for the Mk2s?
Looking forward to your expert advice.
J.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

That's not "AN25", but "4N25". That may or may not work; while the voltage ratings are pretty much identical, the current transfer ratio might be too low for the 4N25 - a mere "higher than 20%", as opposed to the 160-320% for the TCD1124.

1. If you can't get your hands on a TCD1124, similar ones would be CNY17-4 (the -4 bit is important, it's the 160-320% CTR version); CNY174 / CNY17F4; CNY75C; SFH600-3;

2. I wouldn't use a fusible one there; I've got a hunch those aren't necessarily specified for stable values with temperature, but i could be wrong.

3. If the schematic matches the actual circuit that's implemented on the board, it should be fine. Those transistors shouldn't have to deal with anything over 20V or so, and both pairs are rated for 600mA current.

[Jehanne]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Thank you Khron much appreciated.

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I replaced the UC3844N now. The LED is still dead.

To sum it up, what I replaced now:

- C6, C7 (390uF caps)
- C8
- 1uF Cap
- 1N4007 diodes
- 2x IRF840 (Q1 + Q2)
- 10 ohm NTC
- UC3844N

What should I check next?

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

What voltages do you get between pins 5 and 7 of the UC3844? And between pins 5 and 8?

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

What voltages do you get between pins 5 and 7 of the UC3844? And between pins 5 and 8?

With 220v connected and switched on? Can i remove the UC3844 and measure the voltages between the pins then?

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yes, with the circuit powered. With no power, how can you measure the chip's supply voltage, and internal reference voltage?

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Yes, with the circuit powered. With no power, how can you measure the chip's supply voltage, and internal reference voltage?

I thought maybe its possible to power the board with a lower voltage for safety reasons.
Give me a second, i will measure it

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

5-7 3.3v
5-8 0v

Im not an expert but from my guess Q6 and Q7 are next candidates for replacement?

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

With 3.3V instead of 16V or so, no, i quite doubt Q6 or Q7 are to blame.

Are R3 and R4 fine? What about D5 and R5? And Q3 & Q4?

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

R3 and R4 are showing 6kOhm. The value rises slowly to 30kOhm and above when measuring.
R5 5.6 Ohm

--> i get the same readings on the working board


Q3 & Q4 look good, compared with the working board i get the same readings between the pins.

D5 gives same reading on both boards

[Camarada78]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Hello,

I've read the entire thread and found lots of common with mine, did lots of the suggestions and changes and still i got no power.

I'm getting the 340ish volts on the primary, i'm getting the 11-15v on the IC3842, i changed fets, oscialating transistors (4401 and 4403), changed suspicious diodes and so on.

But i get no voltage on the secondary
Secondary diodes and caps are okay, tested outside the board.

I'm not getting any voltage of the opto, 0.2v to be precise, the same voltage i'm getting on the secondary.

Is it possible that the T1 is burned? even though i checked the resistance and they seemed fine (and reconized as inductors on a component tester).

I think the fets are not oscilating for some reason.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Is your C8 ok? 15V is under the official turn-on voltage for the 3842 (which should power up at 16V), but if it slowly rises to that and the chip takes a gulp of current and empties C8, then it would look like the voltage is just ramping up and down.

Can you hear any periodic "tick" sound (like every second or so)? And is the output connected to the amp board?

[Camarada78]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Although it checked ok on the component measurer, I replaced c8 (previously 330uF 35v) with a new one similar with a 330uF, 50v.

i just noticed that i might have fried my 3842 because it is measuring -169v on pin 7 now and -162 on pin 2.

no tick sound.
it is connected to the amp board yes.

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

R3 and R4 are showing 6kOhm. The value rises slowly to 30kOhm and above when measuring.
R5 5.6 Ohm

--> i get the same readings on the working board


Q3 & Q4 look good, compared with the working board i get the same readings between the pins.

D5 gives same reading on both boards

Any suggestions? Anything I could measure?

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Any suggestions? Anything I could measure?

I got it working.

Swapped D5 from the working board and it powered on

Thanks a lot!

[Camarada78]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I got it working.

Swapped D5 from the working board and it powered on

Thanks a lot!

Did you use a BAV21 or a 4148?

[filth]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

I used a BAV21 from my second board that is working.

[Khron]

Re: Repairing Alesis M1 Active mk2 Monitor Speakers

Did you use a BAV21 or a 4148?

Either should work. That diode shouldn't need to hold up to more than 20V or so, but there's nothing wrong with going with a higher rating there.

The BAV21 is rated for 250mA while the 1N4148 is only rated for 100-150mA or so. Allowing for some headroom is of course not a bad thing; you're free to use a 1A diode if you wish, as long as you make sure it's a fast-recovery (or perhaps Schottky) type.