recently replaced my cpu with a junkyard cpu...problem solved for a few months..new cpu has recently failed. spent hours unsoldering and resoldering the cpu that just quit working. didnt fix!! is there any other reason that the cpu would stop working? when i bought the car it had a recent brand new cpu installed within 1 year..and when i bought the new cpu didnt work.....i did the resoldering on that cpu 3 times to no avail.

imm looking for maybe a side problem that could cause the cpu to fail..like i said ive tried several cpus after resoldering and no permanent fix!! the junkyard one worked for awhile but has failed and i removed 99%of the solder and replaced with new solder...am i soldering tooo hot? this cpu did show signs of life, but only for a few seconds then i resoldered again..and again after i plugged it in it worked for a few seconds then stopped working. i have done resoldering on window wipers a few times and had no problems(replaced old relay) for various cars...also done the idiot light thing for a few cars and had no problems...i dont think im soldering wrong cuz other things have worked. i really feel there may be a side effect working against me in another area?

i want a brand new curcuit board so i know theres no old solder...any ideas? i will eventually replace all the diodes and other little things as well as resolder AGAIN!!

thanks for input, all is helpful!!

 

a side fact is: the cpu that did work for awhile did stop working after i got a little rain on the inside of the vert. sprinkles that only got on the center cosole that has the security light..after that..the cpu has gone haywire!! it didnt seem like any rain came in long or hard enough to short out the security light but maybe this is the base of my prob?

 

Ugh, as you have resoldered and replaced the CPU several times I believe your problem may lie somewhere else in the circuit. Next step should be to check all of your fuses. Make sure they're not blown and not the wrong amperage. Let us know how that goes.

B

 

You're going to have to check your wiring. Something is seriously wrong somewhere, and probably shorting out and frying the CPU.

 

What circuits are failing in the CPU??? I am extremely skeptical that all three (or two for a S5 car) boards smoke completely.

Vert CPUs tend to also get damaged if the driver's A pillar door seal gets damaged and then the car is exposed to water. The water runs down the A pillar and into the CPU. It’s pretty easy to see the water damage on the plug and PCBs though.

*edit
I rebuild CPUs all the time, and often see people that have re-soldered them use way too much heat and sear the traces loose on the board. These will tend to smoke after about 5 seconds on being powered up. Make sure when you are soldering that you are not using a larger than 25 watt soldering iron (preferably 15 watts) or a temp adjustable soldering station.

 

icemark i used a 30 watt setting on my gun to get all the solder off. this may be my problem? i notice that the clear sealant stuff on the board turns brown alot when i do the unsoldering. also hear some sizzling sounds in the lowere part of the board when delsoldering. problem is that the 15 watt setting soesnt seem to heat up the old solder enough to get all removed. none of my seals leak when it rains unless i dont open the doors to roll up the windows.

the cpu that did work looked really clean when i opened it up the first time!! looked brand new. also right before i did the first resoldering that cpu didnt work for weeks but when i removed the big plug and replaced it the functions came back. but i figured it was bad solder on the board so i first desoldered and resoldered the coonecters since then no worky!! i can get all diodes and such from the store..and i have an untouched cpu that doesnt work. if i remove all pieces and replace all pieces with new ones..after i unsolder the board..will this approach work? also you say you use the 15 watt setting? my gun is not old but the 15 watt setting doesnt seem to heat up good enough to really liqyify the solder.

maybe i was trying to work too fast with the higher setting!! and thats the cause of my prob?

 

Yes that sure could be the case, from your description; you just might be getting the board too hot.

The conformal coating will melt off when re-soldering, but the components and traces are very heat sensitive. Relays and board connectors are a little more forgiving, but the components will be wasted from too much heat. You might try using a clip on heat sync to dissipate a little of the heat if you are trying to re-solder the components as well

 

definitly use a heat sync whenever soldering something with all sorts of tiny circuits such as your cpu, its incredibly easy to melt stuff and ruin the thing, i know from experience and it sucks

 

I would say your zeal to get "all" the old solder off is unwarrented. Remember, it's just melty metal.
If it's got a lot of contaminants like corrosion or dirt in it, perhapse you should get another CPU anyway. In this case, you have done that already. If it's relitivly clean in there, you only need to re-melt the solder and make sure it's getting sucked in to the wire and making a good solid connection to the boards.
And do try not to melt the boards, they tend to go all non-workie when they get too hot.

Cory

 

No, that will result in the same problems as the imasen factory had.

You do need to remove the old solder. Just re-heating will work for a little while but eventually the same problem will happen again, unless you remove the old solder and flow in new.

 

How are you removing the old solder? Solder wick or vacuum thingy? Also, you are using acid free rosin core soldeR?

James

 

I use a solder sucker, I never had much luck with braid..

 

i sucked the large amounts off with the sucker..then followed up with the braid. especially used the braid for the smaller and closer together joints.