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Discussion in 'Backline' started by colonel kurtz, May 22, 2012.

  1. colonel kurtz

    colonel kurtz Member

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    one of my alesis M1 620 monitors recently started acting up, and after doing a bit of research, i've found that there's a design flaw in these monitors that places one of the capacitors too near to a resistor, which causes the cap to fail and obviously the monitor with it

    i figured swapping out a cap would be easy enough, but upon opening the thing up, i found that it had not only failed, but completely leaked/melted all over a smaller resistor that's mounted next to it on the PCB(not the same resistor that causes the cap to fail)

    now here's the question...with the resistor covered in all the crap that came out of the cap, should i just assume it's also toast and change it as well? i'd prefer not to if possible, because i don't know what the resistor value is, and it looks like removing it is going to be a bitch. more than anything, i'm afraid of damaging the PCB while scraping all the shit off to get the resistor out...but i also don't want to order the caps online, fix it, then find out that the resistor also needs changed and have to wait another week and pay another shipping charge to get a resistor. i have a band coming in this weekend to start pre-pro on an EP, and while i can get away with using some regular bookshelf speakers for that, i need to have this monitor fixed before we start tracking in about a week...any advice would be much appreciated, because really all i know about this shit is how to pull off some basic soldering!
     
  2. sprack

    sprack Thread Killer

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    The resistor probably is still good. But maybe not for the long term. The problem is that its corrosive and conductive so you really should replace anything it's touched. Probably also need a higher voltage cap in replacement. If it's not in the signal path a poly or ceramic would be best. If it's a filter cap most likely your only choice is another aluminum electrolytic.

    You'll have to clean that off the board with some distilled water to get most of the electrolytic off, then some isopropyl alcohol. Q-tips and some lab brushes you've cut back close to have really coarse bristles will get most of the way. Is it surface mounted?

    Best of luck and post some pics of it. I love gut shots.
     
  3. colonel kurtz

    colonel kurtz Member

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    [​IMG]

    here's a pic of the damaged components...pretty easy to see where the black capacitor in the middle has pooped all over the PCB. after looking a little closer, it looks like it's a small diode that it leaked on, not a resistor, and the resistor next to the cap that's marked R4 is the offending component that causes the caps to fail in these
     
  4. JakeAC5253

    JakeAC5253 Frozen Sun Audio

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    Honestly the resistor/diode/whatever it is probably costs under 25¢ for a top quality replacement unit. High quality low tolerance components are deathly cheap these days, unless you need a high wattage rated one, those will run you. Half Watt is fine for most audio signal purposes, just order any parts you THINK you will need and pay one shipping charge for them all, the shipping will cost you infinitely more than the component cost.

    Like Sprack said, go up on the voltage tolerance on the electrolytic, buy radial electros, and mind the component dimensions because you don't want to buy a cap so big that it does not fit in the area it was designed for.
     
  5. Plendakor

    Plendakor Member

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    scrub the board with a toothbrush and methyl hydrate which you can find where they sell paint or wallmart probably (3$)
    btw, short the large cap before you work in there
     
  6. sprack

    sprack Thread Killer

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    #6 sprack, May 23, 2012
    Last edited by a moderator: Nov 20, 2015
  7. colonel kurtz

    colonel kurtz Member

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    thanks for the replies, guys...that vid is actually the 1st thing i found the other night when i started trying to diagnose the problem

    thankfully i found another site that goes pretty in-depth into the issues with these PSU's, and someone listed the value of the diode that got shat all over in mine, and several people also recommended changing another cap on the outside edge of the board, so it looks i'm going to order 2 of each part, swap the components of both of my monitors(since it's apparently only a matter of time until the other dies) and will post results back here when all is said and done

    not sure how to do this. i know that caps are known to store high voltages within them, but like i said before - really the only knowledge i have on electronics is wielding a solder iron, so yea...
     
  8. JakeAC5253

    JakeAC5253 Frozen Sun Audio

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    To discharge the cap you will want a large high wattage resistor like a 470k 2W type. Use an alligator clip and wire to attach the resistor to one lead on the cap, and touch the other lead of the resistor to a piece of metal that's not in the circuit, like metal chassis. After the initial burst of energy, you can use a smaller resistor to more quickly drain the cap of its charge. I shouldn't have to mention that this process is dangerous and you should not use both hands at the same time or if you conduct a charge it will deflect across your chest, so keep one arm at your side.

    Another way to do this is by using a screwdriver shaft, touch both leads of the cap and it will drain into itself. This will create a large dangerous spark and could potentially harm the cap, or the board, or yourself. This is not the recommended way of doing it.
     
  9. sprack

    sprack Thread Killer

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  10. colonel kurtz

    colonel kurtz Member

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    weird how in the 2nd pic, what's labeled there as C14 is C8 on my board(and others i've seen pictures). i'm wondering if that pic might be to the original M1 actives, rather than the M1 620? either way, i'll definitely be doing both, because i noticed some people claiming a difference in the sound of the monitors after the cap change...even if it's all placebo, i'm sure the other monitor will fail at some point as well, so may as well do both

    also thanks for the tip on discharging the cap...looks like i'll need to order one of those resistors as well. now that i think of it, i think the value you stated is the same as the resistors that kill that C8 cap, maybe i can pick a couple of those up and swap the resistors as well to distance the parts from each other
     

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