It's likely the cracked solder joints are caused by the mass of the large
resistor vibrating and the solder fatiguing. After enough flexing solder
tends to crystallize & crack.

I've repaired enough Mercedes climate control relays by reflowing solder
joints that looked perfectly good. The MB climate control relays are really
small modules that compare the RPM of the compressor with the RPM of the
engine & shut the compressor down if the difference is too great.

Tom
www.kegkits.com

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of
Richard Koerner
Sent: Thursday, April 15, 2010 6:02 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: ECU fixed! was: spare ECU?

Think reflowing the solder joints on a 25 year old printed circuit board is
worthwhile preventive maintenance?� Or, if it aint broke, don't fix it?�
Just looking for an opinion.....

Rich
San Diego

--- On Thu, 4/15/10, mark drillock <mdrillock@COX.NET> wrote:

From: mark drillock <mdrillock@COX.NET>
Subject: Re: ECU fixed! was: spare ECU?
To: vanagon@GERRY.VANAGON.COM
Date: Thursday, April 15, 2010, 3:37 PM

Yes, for the resistor legs I used a solder sucker to clean out the old
solder and then added fresh. For the transistors I just added some.

I have another bad ECU of the same version, Bosch 022, and I just re-did the
same solder stuff on it but it made no difference. I wasn't surprised as
there was some evidence of overheating on one of the circuit traces andit
didn't cycle the fuel pump on power up so I knew it likely had a deeper
problem.

Mark

miguel pacheco wrote:
> Mark, did you vaccum out the old solder? I'm curious because I have a 
> small stack of ECUs in the gai-rage.
> Miguel
>
> On Thu, Apr 15, 2010 at 2:11 PM, mark drillock<mdrillock@cox.net>� wrote:
>> So, my friend dropped by this morning with his bad ECU. I plugged it 
>> into my 87, sure enough fuel pump cycled with key on, fast cranking 
>> but would not start. He picked up a spare from me and left. I took 
>> the case off the ECU for a look. I could see some heat damaged solder 
>> joints where a big resistor was soldered into the main board. With my 
>> ohm meter I determined that the resistor fed the big transistor that 
>> runs the fuel injectors. I added new solder to the 2 resistor legs 
>> and took the ECU out to the van for a test, with the case still off. The
van fired right up!
>> ................
>>