Thread: DME failure :(
View Single Post
      11-20-2012, 09:17 AM   #25
themyst
Major General
South Korea
86

 
themyst's Avatar
 
Drives: E90 335i LCI
Join Date: Feb 2009
Location: NYC


Posts: 6,602
iTrader: (8)

Send a message via AIM to themyst
Quote:
Originally Posted by ajm8127 View Post
It is not quite that easy. The MOSFETs that seem to go bad in DME are surface mount parts not through hole parts like the power resistor mod in the JB4. They can be challenging to hand solder because the package is specifically designed to shed heat. It can be made more difficult if there are full power and ground planes inside the circuit board as is common in multi-layer high density digital boards. It can be further complicated if you apply too much heat and burn the glue used to adhere the copper foil to the fiberglass substrate. This can result in "lifting" pads off of the substrate.

It is typical to use a board pre-heater to help warm the board up before applying the heat directly to the part to melt the solder, specifically with large parts like high power surface mount MOSFETs Hot air guns are also common in surface mount soldering. These are not the same as the ones you buy at the hardware store to strip paint. The temperature is precisely regulated and the air flow volume is considerably less than paint stripping models.

Considering the high price associated with replacing the DME, ensure you know what you are doing before you attempt to replace parts on the DME PCB.

I'm not trying to pick a fight, but I have a good bit of experience in this area, and I know just how much of a pain it can be. Without the right equipment and experience, you can have a costly mistake on you hands. However, using care and the right tools, surface mount soldering high power packages by hand is doable.
Well aware of what needs to be done. No hand job will be nearly as pretty as it came from the assembly but the point is it can be done, just much more time-consuming than something like a JB4.

Other option is to buy a new DME and have it recoded, pay hundreds to fix it.
__________________
E90 LCI N54 6AT