Mosfets, Swords and goop

[Kibokojoe]

I am attempting to repair my sword/final stage. Anyone know what the purpose of the plastic/epoxy goop that is applied on the circuit board just above the mosfets? I slid an exacto blade under the edge of the goop and they popped right off. Do I need to reapply this goop once I solder the new mosfets in? I am assuming the aluminum blade is for heat dissipation so I will need to insure the heat sink on the mosfet is right up against the blade.

[myles]

I thought that it was to prevent it from deteriorating with age. Make sure you check for dry solder joints where the connector plugs onto the PCB. That was the source of the problem for me.

[pundit]

I am attempting to repair my sword/final stage. Anyone know what the purpose of the plastic/epoxy goop that is applied on the circuit board just above the mosfets? I slid an exacto blade under the edge of the goop and they popped right off. Do I need to reapply this goop once I solder the new mosfets in? I am assuming the aluminum blade is for heat dissipation so I will need to insure the heat sink on the mosfet is right up against the blade.
Are you certain the mosfets have failed?
Although mosfets are commonly referred to as being the reason swords fail I am inclined to doubt they fail all that often.
Have you checked out this thread?

http://www.bimmerboard.com/forums/posts/91956

and this one...

http://www.bimmer.info/forum/showthread.php?t=17751

[shogun]

Here are many actual pics from Shayne about the repair.
You do not need to reaply the epoxy covering. it is used specifically for tamper control as the entire assembly is coated. You do need to reapply the Conformal Coating.

http://www.bimmerboard.com/forums/posts/355700/
http://www.bimmerboard.com/forums/posts/355705

[Kibokojoe]

Are you certain the mosfets have failed?
Although mosfets are commonly referred to as being the reason swords fail I am inclined to doubt they fail all that often.
Have you checked out this thread?

http://www.bimmerboard.com/forums/posts/91956

and this one...

http://www.bimmer.info/forum/showthread.php?t=17751
Replaced the mosfets this afternoon. Looks like that was the problem. Now I need to look at the blower motor. Its old and I think it maybe drawing too many amps. Anyone know how to test the blower?

[shogun]

Maybe the carbon brushes are worn. Gale has a repair instruction on his site. Link on my website below.

[shogun]

or just change the motor with the drive shafts
http://www.bimmerboard.com/forums/posts/438091
http://www.bimmerboard.com/forums/posts/438056/
http://www.bimmerboard.com/forums/posts/438133


someone wanted to try a cheaper Siemens blowe motor from Autozone, but he never reported back if it fits as per the online info, here the thread
http://www.bimmerboard.com/forums/posts/437479

[Kibokojoe]

I learned a good lesson today. Don't leave any flux on the Mosfets after you solder them. Last night when I got home I noticed that the blower would not shut off all the way off. I took out the sword and started pushing around on parts on the PCB but nothing helped, until I took a small screwdriver and cleaned between the mosfets solder joints. Once I did that the blower shut off. Tonight I noticed that the fan would not shut off again. I am thinking about pulling out the sword again and cleaning those joints with contact cleaner and then respraying them with silicone conformal coating once again. Perhaps this will fix the problem. I am thinking that once the mosfets get hot the flux gets hot and builds up continuity between the solder joints. Does this sound logical. Any ideas?

[shogun]

just to add these nice pics for future reference
http://www.cafeim11revier.de/ebay/heitzschwert_teile.pdf