Question about Alesis M1-Active MkII Main / Stereo Speaker
Hello, My Alesis M1 ACTIVE MONITOR amp circuitry board is ticking at Ac power frequency; which is also indicated by the LED flashing and the periods of sound loss. I think it may be the capacitors on the amp. Would be gratefull for some advice and guidence. Also i would be grateful for any links in reference to repair.
The flashing blue LED and loss of sound on the Alesis M1 powered
monitor is caused by failure of capacitor C8 (220uF, 35V) on the power
supply board. It dries up due to its proximity to resistor R4 (47K, 2
W) which gets very hot. This is a design fault.
Remove the power supply board (4 corner screws and 2 mains connector screws) and disconnect the two plugs. Carefully desolder C8 and replace it. Its value is not critical (220 to 470 uF will do) but it should be a 105 deg. type, preferably at 50V.
Remove R4 and replace it with a similar resistor with its leads bent so that it is nowhere near C8, otherwise the fault will return. One end may be connected to one of the existing R4 solder pads (furthest from rear of board), and the other to the top end of resistor R3. Check that you have connected it correctly by inspecting the PCB tracks.
Replace the board and all screws and plugs before testing.
Posted on Nov 28, 2007
Had the blue light flicker of death. Fixed this issue with a 330uF 35V cap. Sounds just fabulous now. I did get the cap out of the radiant spell of the resistor utilizing the longer leads and insulator for the leads. I had 2 months left in my warranty but figured paying for shipping to Alesis and at least 2 weeks wait just didn't compare to the $2 I spent with a local electronics shop.
Kudos folks. I've been unemployed for 6 months after a layoff and was really bummed until I found this site.
Posted on Mar 13, 2009
I own M1 Active 620. I changed the C8 capacitor with a 220 microfarad under 50V 105 deg type, wich fixed the problem only with one monitor.
The other one is still warm when you put the hand on the back of the monitor, you feel it.
I have changed the resistor on the other monitor with a 47k ohm under 2w and it don't works. This resistor is bigger than the original and it's impossible to read the value of the resistor because of the thermal interface material ( which confirms this piece gets hot)
So i've done a measure with a multimeter:
The original R4 resistor on Alesis M1 active 620 is 2,5 Mega ohm. I don't see how it could work with a 47k resistor!!!
I will change the resistor with a 2,5 M ohm (under 2w?)and tell you if it's Ok
Posted on Nov 06, 2008
How do you take the board out of the box from a 520 model? I unscrew everything but nothing moves. All I could remove was the subwoofer speaker.
Posted on Jun 09, 2016
Using a smaller capacitor would reduce the bass response on 'high power', the capacitors supply the extra current the peaks of the music like the kick require, without that extra current there isnt the power available to fully deliver those kicks - unless they had used an overrated power supply which can supply it straight off the plug but thats more expensive and wouldnt make them as much profit :P.
i used 440uF caps for C8, long as the voltage is the same its all good, and oversized capacitors can never hurt!
Posted on Sep 06, 2012
I changed out C8 and it did fix my problem, but The C8 cap in my M1 was a 330uf. I replaced it with a 220uf because it was that or a 470uf (all that was available). When I played the speaker I can hear a slight lose of bass response with the 220uf instead of the stock 330uf. It's enough of a difference that I'm getting another 330uf and changing the C8 out again. Sounds like I have the 1/2 space switch on.
I appreciate the help and information, but thought I'd add what my ear and eyes observed. Also the cap I bought had long leads and I manged to install it away from the resistors and accomplished getting the cap away from the heat without having to move the resistors.
Thank you rayhow for the information! Very helpful.
Posted on Sep 28, 2008
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