Re: Mystery no start issue
Originally Posted by tighed1
Don't know if I mentioned it but at some point Mercedes changed the part number on the RCM. Think I read somewhere that it was related to a recall. Maybe they have addressed the problem with the newer part?
The part that is used on all Crossfires is the Mercedes part #A170 545 03 05.
The part mentioned in Mercedes forums with the same problem was part #A210 540 00 72.
The problem as I see it is caused by 'cold joints'. That is when the parts or one or more parts being soldered do not get hot enough for the solder to adhere.
In our case the terminals that are soldered are the ends of a buss bar, this buss bar is copper and having a substantial mass in relation to the PC board loses a lot of heat by conduction through to the large copper mass on the other side of the board. Heat applied to the joint will heat up the board enough, which is only a thin copper sheet, but heat applied to the terminal itself will have the heat rapidly wicked away so that it is never becomes hot enough even though the board allows solder to run around the the terminal.
The 'crack' is not due to vibration or heat but due to the cold terminal when the solder was applied. Such joints will look different depending on how much heat was applied, they could look nearly perfect or the flaw is very obvious when both terminal and board were not hot enough and the solder never really was molten.
Only use solders and fluxes suitable for electronics, that bit of solder you used to solder copper pipes in your basement is no good. Solders are molten at temperatures that vary by 100deg F. You want to use the low melting point grade, 360deg F (60/40) not 460deg F.(40/60).
Last edited by onehundred80; 05-01-2011 at 04:54 PM.