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Alesis M1 Active died, burning smell
Old 25th May 2020
  #1
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Alesis M1 Active died, burning smell

Hi everyone,

My Alesis M1 Active 360 died while giving off burnt plastic smell. The attached image shows the only place on the PCB that shows sign of damage. I'm not an engineer so I'm not sure if the damaged part is the coil shown in the image or the component next to it.

I'd appreciate your feedback, plus how to remove the charred goo without damaging the PCB.

Thanks.
Attached Thumbnails
Alesis M1 Active died, burning smell-alesis.png  
Old 25th May 2020
  #2
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Fay Smearing's Avatar
 

Looks a bit like a capacitor had a dishonorable discharge. It'd help to either get the circuit diagram or a look at an undamaged one. Do both monitors run of one set of electronics or are both powered individually? There are different versions according to quick search.
Old 25th May 2020
  #3
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Hi Fay,

Each monitor is powered individually. There is only one capacitor near that area and it is not damaged. I'm thinking of replacing the copper coil piece but I don't know how to remove the glue that surrounds it, especially the part that has been charred.
Old 25th May 2020
  #4
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The coil would be about the last thing to die on the board. It doesn't look like it overheated or anything; the yellow wrapper is nice and fresh looking, for instance.

It does look like a component just below the coil (in the picture) and next to the half-covered diode self-destructed, and I would also guess that's an electrolytic capacitor. I'd suggest comparing the board in the good monitor to this one to see what components should be there. If it's an electrolytic capacitor there, it may be wise to replace the one in the other monitor also as a preventative measure since they're most likely from the same batch, making the assumption that the monitors were bought together originally.

There's a bit of work in cleaning the burnt goo off the board, too. It wouldn't hurt to check other components if practical in the area to see if they need replacement, such as the resistor near the lower-right corner of the photo and the diode next to the coil. Chances are pretty good that they're okay, in my estimation.
Old 26th May 2020
  #5
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Thanks, DrewE and Fay for your feedback. Any tips on how to clean the burnt goo without damaging the PCB?
Old 26th May 2020
  #6
Gear Head
 

Quote:
Originally Posted by amu View Post
Thanks, DrewE and Fay for your feedback. Any tips on how to clean the burnt goo without damaging the PCB?

Hey amu, there are various methods to clean the PCBs. Here are the helpful tips, you can follow any of these..

https://gesrepair.com/clean-circuit-board/
Old 28th May 2020
  #7
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Thanks, msbettyhunt.
Old 28th May 2020
  #8
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kludgeaudio's Avatar
 

Okay....I spent a couple minutes with google. Here is a better view of that board:

http://www2.neufeld.newton.ks.us/ima...0/DSCN1235.jpg

You can see here D16 and D14, and you can see D14 is in parallel with C40 and they are on the high voltage primary side of the board. (This is from an article where C65 failed, but you C65 does not look obviously bad). It looks to me like your D14 failed. Why would this happen?

Hmm, looks like someone has a bootleg service manual on the internet...
https://manualzz.com/download/22864807
Page 14 marked "B6 converter" is the power supply board and you can see that this stuff is on the big power transformer driving the primary side.

Get out the meter and set it to continuity, Test D14 and D16 and I bet at least one of them will test as shorted. They are both likely to be bad. Why would D14 blow up like that? Likely because Q2 has failed into a short. Again, get the continuity tester and I bet all three pins test as shorted together.

Test D6 and Q5 in circuit... if they test okay, keep them. Damper diodes like D16 should always be replaced whenever anything else in the circuit blows up because they can test okay and still be bad at high voltage. Test Q1 while you are at it... if it is bad, all three pins will be shorted because they fail "wiped" with metal sprayed across the surface of the die. If Q1 tests as bad, it has likely destroyed everything attached to the gate, including Q3 and Q4, and that is likely to take out U1 as a consequence, but if you're lucky Q1 will be okay.

The way these things fail, either the power transistor fails and takes out the damping diode, or the damping diode fails and takes out the power transistor, but then you start getting cascading damage from the high voltage on the source and drain suddenly coming out of the gate on the transistor.

Repairing this stuff is not bad but you need to make sure you get everything cleaned up or you can wind up in a situation where it seems to be running just fine but one of the damping diodes is bad and a week later it blows up again. The damping diodes exist to protect the transistor.

If you're not comfortable working with a soldering iron and a scope, print this out and print out the service manual and take it to your local TV repair shop. Anybody who can fix switching supplies for flat panel TVs should have absolutely no problem working on this thing.
--scott
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