Alesis M1 active repair help needed!!
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Topic: Alesis M1 active repair help needed!!
Posted By: mk2_ginger_biscuit69
Subject: Alesis M1 active repair help needed!!
Date Posted: 05 September 2012 at 3:36pm
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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 ------------- ''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it'' ''Dubstep - an elongated electronic fart'' |
Replies:
Posted By: mk2_ginger_biscuit69
Date Posted: 05 September 2012 at 10:36pm
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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'' |
Posted By: mk2_ginger_biscuit69
Date 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'' |
Posted By: service dept Steve
Date Posted: 06 September 2012 at 3:54pm
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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?
------------- We are not "They", We are "The others" http://www.servicedept.co.uk" rel="nofollow - http://www.servicedept.co.uk - |
Posted By: mk2_ginger_biscuit69
Date Posted: 14 September 2012 at 8:27pm
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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].
------------- ''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it'' ''Dubstep - an elongated electronic fart'' |
Posted By: service dept Steve
Date Posted: 14 September 2012 at 8:39pm
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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.
------------- We are not "They", We are "The others" http://www.servicedept.co.uk" rel="nofollow - http://www.servicedept.co.uk - |
Posted By: mk2_ginger_biscuit69
Date Posted: 14 September 2012 at 9:12pm
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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'' |
Posted By: service dept Steve
Date Posted: 15 September 2012 at 5:33am
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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. ------------- We are not "They", We are "The others" http://www.servicedept.co.uk" rel="nofollow - http://www.servicedept.co.uk - |
Posted By: mk2_ginger_biscuit69
Date Posted: 15 September 2012 at 4:32pm
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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  .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'' |
Posted By: Earplug
Date Posted: 16 September 2012 at 11:00am
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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... ------------- Earplugs Are For Wimps! |
Posted By: mk2_ginger_biscuit69
Date Posted: 16 September 2012 at 12:34pm
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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!]. ------------- ''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it'' ''Dubstep - an elongated electronic fart'' |
Posted By: mk2_ginger_biscuit69
Date Posted: 16 September 2012 at 1:00pm
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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 ------------- ''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it'' ''Dubstep - an elongated electronic fart'' |
Posted By: Earplug
Date Posted: 17 September 2012 at 5:44pm
Haha - they say that 90% of the problems with electronic gear comes down to bad solder joints...  ------------- Earplugs Are For Wimps! |
mk2_ginger_biscuit69 wrote:Posted By: odc04r
Date Posted: 17 September 2012 at 6:36pm
I wouldn't advise spreading it, just put a small rice grain or a bit smaller in the centre of the package and then slowly tighten the mounting bolt. But over the front of the package use a washer or small plate to evenly distribute the force. The actual die inside is not going to be an bigger then 5mm square, probably smaller so all you really need is good heat distribution from the centreof the package to the heatsink. If I used a Stanley blade I would be concerned that it might be too thin somewhere. Of course too thick is bad as well.
Even better than a solder sucker is some solder wick. In fact it is 10x better. Also some flux for reworking. |