Problem with MQ430

Post by **joerg** » Sun Apr 18, 2010 9:06 am

After a long time i´m in the process of finishing my FAS now. I manged to get the MS2125 side working again. Now i have a problem with the MQ430 in it. Powers up fine but after a few seconds one of the small fuses blows.
Thanks for input if u have an idea what could be the reason.

marko · Post by **marko** » Sun Apr 18, 2010 10:09 am

have you checked current draw? possibly there's a short on ps side of things... does the other side work ok?

Post by **joerg** » Sun Apr 18, 2010 10:39 am

The other side is fine and works perfect

marko · Post by **marko** » Sun Apr 18, 2010 10:56 am

thinking again, if one side works ok and i notice the amp only has one transformer then i reckon you have issues with a fet on the output side of things.. i would start ohming out the fets to see if any are shorted. there's also a possibility that when/if the board has been refitted a slither of wire got caught up behind a fet and is shorting it out

Post by **Eric D** » Sun Apr 18, 2010 11:36 am

If the amp used to work fine, but the act of taking it apart and putting it back together caused a problem, I am pretty sure you have an issue with a sil-pad somewhere. Pretty much what marko is saying.

nico boom · Post by **nico boom** » Fri Apr 30, 2010 11:21 am

Eric D wrote:If the amp used to work fine, but the act of taking it apart and putting it back together caused a problem, I am pretty sure you have an issue with a sil-pad somewhere. Pretty much what marko is saying.

I second that; remember what I said earlier about feeling with your fingers across the holes in the sink before re-fitting the board; if you feel any "bumps" around the holes, the very first part of the thread is just a bit lifted [which is normal because self-tapping screws are used].
So I always use a drill about 7mm in diametre and twist it gently with my fingers until that area is flat, or the edge of the hole a bit lower than the sink. This assures, together with a absolute clean sink [every hole cleaned with compressed air] that the silpads will isolate the fet safely from the sink. The older fets sometimes have a small "tube-like" isolator around the screw, those are best measured with a DMM after installation for resistance, making sure they are not connected directly to the sink.
A silpad is THIN and SOFT, making it vunerable for pearcing thru by even the smallest [metal] particle.
A long story short; WORK WITH ABSOLUTE ATTENTION FOR EVERY DETAIL.
I'm sure you will find it Joerg!
Good luck.