Struggling with DME repair...PLEASE HELP

redlineclipse · 05-07-2021, 12:45 AM

Hey guys I did the test on my DME and I have a bad mosfet. I was trying to get someone locally to repair it but can't find anyone close by. So I went ahead and bought a heat station. I've started some things in the past but nothing on circuit boards really. It's almost 2:00 here and I'm about to throw in the towel for the night. I feel defeated and would really like some help if anyone can offer any.

First of all I had to heat the station up to 400C to even get the chip to budge. That was kind of alarming considering everyone has me scared to death of overheating another component. But I was able to successfully remove the chip. After that I lined the track with solder. I took my time and tried to be very precise. I've attached a picture.

The problem I'm having is getting the mosfet to actually sit down on the solder. I don't know if I am possibly using the wrong type of solder. Again I don't know much about this, but I had the typical wire stuff that I've used for other soldering fixes. It melts pretty quick with a soldering iron but it seems like I can't get the heat station to melt it, which means that the mosfet never sits down because the solder never flows. Can someone please tell me what I'm doing wrong? Am I using the wrong kind of solder and the melting point may be too high? Are there any tricks of the trade? I got the chip to sit down two times but not very snug and not completely flush. So I'd start over.

I've been at it for hours and I am going to bed frustrated.
Please help!

hassmaschine · 05-07-2021, 11:35 AM

You need to clean and re-tin the pad. Use a solder wick to remove the old solder, and apply a thin layer (and flux!) for it to stick to, then add more as needed once it's placed properly.

400c isn't that hot really, it's barely enough to melt the solder used on these components. also, they're attached to a thick ground plane, which is why it takes so long to heat it up enough to melt. Next time, use some de-soldering solder - it reduces the melting temp and makes it a little faster.

also be careful because it looks like a couple of those pads are lifting. if you break one off that DME is basically dead (or you have to send it to a pro to be repaired).

E92_William · 05-07-2021, 02:00 PM

Idk if these boards come sealed but if they are chances are you got some of that melted on your tip and it will barely melt anything if it's dirty. When soldering surface mount components I like to put a bit of solder in one of the pads and then putting the component I want to solder in the board with the leg right on top of that pad but already perfectly aligned in the position it will be in, then while holding the component you melt the solder in the pad and the leg falls inside of the solder and the component is set in place being held by the soldered leg, then you can go ahead and do the other. Sometimes SMDs come held down by adhesives.

Of course things mentioned above also play a huge role. Make sure to clean up with alcohol everything after you're done and if it works fine after you finished I recommend sealing the board with some kind of conformal coating to prevent corrosion

gbalthrop · 05-07-2021, 03:16 PM

I don't want to Hi-jack OP's thread, but if anyone can give some first-hand Tips on use of a Heat Station with Hot Air Gun, this Dinosaur who still uses a soldering iron and Solder-sucker would like to move into this millennium.

Here's "Amazon's Choice" for example:
https://www.amazon.com/Tek-Motion-Di...xpY2s9dHJ1ZQ==

George

ZGator · 05-07-2021, 03:29 PM

There is some good tips here - that solder is too heavy - wick it up.

I would suggest to go find some surface mounted circuit boards - got any old computer boards around - or other electric stuff that is heading for the dump? - well go PRACTICE on that with temp, etc, it is a bit of art form - take some components off and try to put them back on, when you get comfortable with that then proceed on your DME.

BTW, I did take my DME out, sourced, and replaced a MOSFET, put it back in, BUT it did not fix the issue - the issue was with another component connected to MOSFET - called a GATE driver chip - it actually does 3 mosfets - there are 2 on 6 cylinder cars.

Worse case, if you can't do it, or it doesn't work, you need to find a replacement DME at junkyard and send it out with original to clone (along with CAS/Key).

05-07-2021, 12:45 AM	#1
redlineclipse New Member 14 Rep 25 Posts Drives: 07 335i Join Date: May 2018 Location: South Carolina iTrader: (0)	Struggling with DME repair...PLEASE HELP Hey guys I did the test on my DME and I have a bad mosfet. I was trying to get someone locally to repair it but can't find anyone close by. So I went ahead and bought a heat station. I've started some things in the past but nothing on circuit boards really. It's almost 2:00 here and I'm about to throw in the towel for the night. I feel defeated and would really like some help if anyone can offer any. First of all I had to heat the station up to 400C to even get the chip to budge. That was kind of alarming considering everyone has me scared to death of overheating another component. But I was able to successfully remove the chip. After that I lined the track with solder. I took my time and tried to be very precise. I've attached a picture. The problem I'm having is getting the mosfet to actually sit down on the solder. I don't know if I am possibly using the wrong type of solder. Again I don't know much about this, but I had the typical wire stuff that I've used for other soldering fixes. It melts pretty quick with a soldering iron but it seems like I can't get the heat station to melt it, which means that the mosfet never sits down because the solder never flows. Can someone please tell me what I'm doing wrong? Am I using the wrong kind of solder and the melting point may be too high? Are there any tricks of the trade? I got the chip to sit down two times but not very snug and not completely flush. So I'd start over. I've been at it for hours and I am going to bed frustrated. Please help! Attached Images
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05-07-2021, 11:35 AM	#2
hassmaschine Major General 3966 Rep 7,215 Posts Drives: "NBO" 330i Join Date: Jun 2014 Location: earth iTrader: (0)	You need to clean and re-tin the pad. Use a solder wick to remove the old solder, and apply a thin layer (and flux!) for it to stick to, then add more as needed once it's placed properly. 400c isn't that hot really, it's barely enough to melt the solder used on these components. also, they're attached to a thick ground plane, which is why it takes so long to heat it up enough to melt. Next time, use some de-soldering solder - it reduces the melting temp and makes it a little faster. also be careful because it looks like a couple of those pads are lifting. if you break one off that DME is basically dead (or you have to send it to a pro to be repaired).
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05-07-2021, 02:00 PM	#3
E92_William Captain 1306 Rep 852 Posts Drives: 2008 BMW 328xi Join Date: Apr 2021 Location: South Florida iTrader: (0)	Idk if these boards come sealed but if they are chances are you got some of that melted on your tip and it will barely melt anything if it's dirty. When soldering surface mount components I like to put a bit of solder in one of the pads and then putting the component I want to solder in the board with the leg right on top of that pad but already perfectly aligned in the position it will be in, then while holding the component you melt the solder in the pad and the leg falls inside of the solder and the component is set in place being held by the soldered leg, then you can go ahead and do the other. Sometimes SMDs come held down by adhesives. Of course things mentioned above also play a huge role. Make sure to clean up with alcohol everything after you're done and if it works fine after you finished I recommend sealing the board with some kind of conformal coating to prevent corrosion __________________ Airplane Mechanic BMW Masochist
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05-07-2021, 03:16 PM	#4
gbalthrop Brigadier General 2647 Rep 4,005 Posts Drives: 2007 328xi E91 Join Date: May 2017 Location: Fairfax Co, VA iTrader: (0)	Heat Station Questions I don't want to Hi-jack OP's thread, but if anyone can give some first-hand Tips on use of a Heat Station with Hot Air Gun, this Dinosaur who still uses a soldering iron and Solder-sucker would like to move into this millennium. Here's "Amazon's Choice" for example: https://www.amazon.com/Tek-Motion-Di...xpY2s9dHJ1ZQ== George
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05-07-2021, 03:29 PM	#5
ZGator Private 33 Rep 70 Posts Drives: E90 328xi, E36/7 Z3 2.3 Join Date: Jul 2014 Location: New England, USA iTrader: (0)	There is some good tips here - that solder is too heavy - wick it up. I would suggest to go find some surface mounted circuit boards - got any old computer boards around - or other electric stuff that is heading for the dump? - well go PRACTICE on that with temp, etc, it is a bit of art form - take some components off and try to put them back on, when you get comfortable with that then proceed on your DME. BTW, I did take my DME out, sourced, and replaced a MOSFET, put it back in, BUT it did not fix the issue - the issue was with another component connected to MOSFET - called a GATE driver chip - it actually does 3 mosfets - there are 2 on 6 cylinder cars. Worse case, if you can't do it, or it doesn't work, you need to find a replacement DME at junkyard and send it out with original to clone (along with CAS/Key).
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