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Alesis M1 active repair help needed!!

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mk2_ginger_biscuit69 View Drop Down
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    Posted: 05 September 2012 at 3:36pm
one of the pairs i have here are buggered, tried the common fix [C8 & R4] as detailed here http://www.gearslutz.com/board/low-end-theory/109491-problem-alesis-m1-active-monitor.html, no joy.

Symptoms are when powered up, 'pulse' every second, with the bass driver excursing in a big sine wave nearly to xmax, powerlight comes on during cone movement.

Any ideas on where to test? I was intending on taking a craic with a multimeter and test components at random to see if i can track any broken parts, but anyone got a more educated guide of where i should be looking?

Cheers, Pat


Edited by mk2_ginger_biscuit69 - 05 September 2012 at 10:36pm
''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 05 September 2012 at 10:36pm
any ideas?
''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2012 at 3:29pm


''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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service dept Steve View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 06 September 2012 at 3:54pm
What are those amps there? LM3886? I assume that you did the obvious, swapped the amp chips, there looks to be a couple of regulators there, are they powering all the way to 15v or is the psu collapsing before they come on? What happens if you mute the amp inputs? (this would show if the fault was with the crossover section or the amp) If it is powered without the speaker does it come all the way on with one of the voltage rails on the speaker output or does it either hang or protect?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 14 September 2012 at 8:27pm
Both fixed now thankyou, the LM3886T on one fixed it, the other needed a LM3886T and Resister R15 0.22ohm 2W in the PSU replacing [not sure what function it had, bar it flew internal fuses before replacement, and had a hole blown in it]. 

Edited by mk2_ginger_biscuit69 - 14 September 2012 at 9:12pm
''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 14 September 2012 at 8:39pm
Good news and thanks for the update, So often is there nothing mentioned and so people answering posts have little clue as to the success or failure of the project.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 14 September 2012 at 9:12pm
one question actually, between the LM3886T chips and the heatsink was white paste, i presume that is thermal stuff like CPU's use? 
''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2012 at 5:33am
Correct. It is heat transfer compound which improves the thermal connection between the tab and the heat exchanger. Often there is also a insulator to electrically isolate the tab from the heat sink.
Hopefully you found enough to mount the chip.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 15 September 2012 at 4:32pm
i saw no insulating tabs, but did use thermal paste [prolima tech] left over from my new PC build, and has been on 24hours now without dieing.

only odd thing is the front power on LED is quite dim compared to the other pair i have, and on powerup there is a slight pop on the LF driver, but just went on the ''if it aint broke dont fix it'' method, they work and sound alright Thumbs Up.

If i ever bump into you steve, i owe you a beer!


''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2012 at 11:00am
It sounds like the muting circuit isn´t working. The dim LED may be a clue, ie one of the required voltages isn´t right. Worth checking that before it goes POP again...




Edited by Earplug - 16 September 2012 at 11:01am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2012 at 12:34pm
once again problem solved, dodgy solder on the 8th LM3886T leg - had solved this before your reply, but never mind.

And getting full voltage to the audio circuits, just a bit down on the LED output which doesnt bother me - they are taped over anyway [far too bright!].


Edited by mk2_ginger_biscuit69 - 16 September 2012 at 12:40pm
''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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mk2_ginger_biscuit69 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2012 at 1:00pm
for the benefit of anyone who comes across this via websearch, ive labeled the parts and where they are:

switchmode power supply board

in GREEN = R4 [resister4 47K, 2 W] + C8 [capacitor8 220uF, 35V]

i replaced C8 with 470uF @ 50v 105degree type, leaving the legs long to be well away from R4 to stop it cooking to death!

in YELLOW = R15 [resister15 = 0.22ohm 2w]


crossover/amplifier board

in RED = low frequency amp chip LM3886T 11pin. Be sure to use thermal paste between module and the heatsink it bolts onto. I find to get a consistant thin layer, put on a 'blob' in the centre, then spread with a stanleyknife blade - this will give you a smooth consistant level [same for installing computer CPU heatsinks].


Bare in mind you will need a steady hand when soldering components - if you havnt soldered before try building a random circuit first! A solder sucker is vital for clearing solder to remove components.

Good luck



Edited by mk2_ginger_biscuit69 - 16 September 2012 at 1:03pm
''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

''Dubstep - an elongated electronic fart''
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