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View Full Version : Bad Day FET Fix


LBRC
2006.06.04, 01:11 AM
Ouch :(
http://lbspd.com/v-web/gallery/albums/album106/The_consiquence.jpg
Perfectly good FET stack decided to go yesterday.
http://lbspd.com/v-web/gallery/albums/album106/Likely_cause.jpg
The exposed power switch wire shorting to this via (hole through CB) that connects directly to the left FETís P-channel input could have been the cause of the meltdown. Unfortunately while removing the burnt stack the N-channel signal input pad lifted and broke off. Additionally what is not that easy to see in the first photo is that the run leading from the via to the P-channel input was also damaged just before the pad fortunately that was easily fixed with a little solder to bridge the run. Unfortunately the missing pad took a bit more work.

http://lbspd.com/v-web/gallery/albums/album106/Jumper.jpg
The first thing that needed to be done was to build a new stack hoping that the other stack was still good, and since things are a little tight in a MR-02 it helped to solder on the jumper wire before trying to install the new stack.

Then it was just a matter of using a multimeter to find a convenient spot for the jumper, soldering on the new stack and connect the wire. BTW itís a big time saver if you use the multimeter to make sure everything is perfect, no shorts, no opens, and good connections prior to reinstalling the CB.

http://lbspd.com/v-web/gallery/albums/album106/Fixed.jpg
All better, car works great. :cool:

kittysniper101
2006.06.04, 10:02 AM
Ouch :(
http://lbspd.com/v-web/gallery/albums/album106/The_consiquence.jpg
Perfectly good FET stack decided to go yesterday.
http://lbspd.com/v-web/gallery/albums/album106/Likely_cause.jpg
The exposed power switch wire shorting to this via (hole through CB) that connects directly to the left FETís P-channel input could have been the cause of the meltdown. Unfortunately while removing the burnt stack the N-channel signal input pad lifted and broke off. Additionally what is not that easy to see in the first photo is that the run leading from the via to the P-channel input was also damaged just before the pad fortunately that was easily fixed with a little solder to bridge the run. Unfortunately the missing pad took a bit more work.

http://lbspd.com/v-web/gallery/albums/album106/Jumper.jpg
The first thing that needed to be done was to build a new stack hoping that the other stack was still good, and since things are a little tight in a MR-02 it helped to solder on the jumper wire before trying to install the new stack.

Then it was just a matter of using a multimeter to find a convenient spot for the jumper, soldering on the new stack and connect the wire. BTW itís a big time saver if you use the multimeter to make sure everything is perfect, no shorts, no opens, and good connections prior to reinstalling the CB.

http://lbspd.com/v-web/gallery/albums/album106/Fixed.jpg
All better, car works great. :cool:

hey LBRC I think it would help everyone out a lot if you could show us where to solder the jumper for each of the signal lines on both mosfets for those who are less inclined with a multimeter

LBRC
2006.06.04, 04:45 PM
hey LBRC I think it would help everyone out a lot if you could show us where to solder the jumper for each of the signal lines on both mosfets for those who are less inclined with a multimeter
Sorry but the concept of someone wanting to try stacking and/or soldering mosfets yet alone making repairs after damage to a CB without the use of at least an inexpensive digital multimeter is so far beyond the scope of my imagination that it makes the hairs on the back of my neck stand up, in fact Iím having a hard enough time just grasping the concept of someone simply using or having access to a soldering iron without a multimeter, it gives me the willies such an abomination violates the natural order of the universe.

I donít mean to sound all pompous, pious, or anything else like that itís just that in my opinion the best help and chance for success I can think of for anyone who wants to try is to tell them to get a multimeter, read up on how to check for continuity if they donít know how, find a magnifying glass and spend some serious time seeing how it all works before they try. That way they will also be able to check for shorts, preventing further irreparable damage, prior to applying power.

Spoon
2006.06.04, 05:04 PM
Sorry but the concept of someone wanting to try stacking and/or soldering mosfets yet alone making repairs after damage to a CB without the use of at least an inexpensive digital multimeter is so far beyond the scope of my imagination that it makes the hairs on the back of my neck stand up, in fact Iím having a hard enough time just grasping the concept of someone simply using or having access to a soldering iron without a multimeter, it gives me the willies such an abomination violates the natural order of the universe.

I donít mean to sound all pompous, pious, or anything else like that itís just that in my opinion the best help and chance for success I can think of for anyone who wants to try is to tell them to get a multimeter, read up on how to check for continuity if they donít know how, find a magnifying glass and spend some serious time seeing how it all works before they try. That way they will also be able to check for shorts, preventing further irreparable damage, prior to applying power.


I don't think you are being pompous or pious. It's a very small number of people that don't know how to use a multimeter that still have the skill to solder Surface Mount Components. Don't get me wrong, there are a few, but the fine soldering skills that it takes to do a FET replacement (and especially a stack) should come with some knowledge of how to use a multimeter.

There's been more then one member on these boards that assumed that it was as easy as bye-bye makes it look to do a FET replacement (prop's to bye bye on that ;) ) But a lot those folks end up with lifted pads shorted leads, etc that have no idea how to fix them.

I also get the "hairs on the neck" when I see that some one is going "grab a sodlering iron" and "see how it goes" It usually goes poorly.