Question : Problem: One memory card slot not working after soldering to mother board

The slot for the second memory card on the motherboard adjacent the two main chips and the heat sink fan is not working - I had an overheating problem, got a new main heat sink assembly and fan and soldered a jumper wire and loop across HS2 on the board from the top.  The original card in the second slot (adjacent the heat sink devices and the HS-2 slot) did not work when I restarted the machine; removing that card allowed the machine to boot up and operate, although slowly (with only 256 MB).  I replaced the original and second cards with Kingston 1-G cards, but the second card slot does not work either.  Nothing looks amiss from above.  Could my soldering the jumper across HS2 have goofed up something under the motherboard, or is there likely another problem?  Please advise on analysis and repair.  Thanks.

Answer : Problem: One memory card slot not working after soldering to mother board

Check for solder hairs or droplets. (Bridging a gap.)

Check that you didn't scratch a solder trace/run on the board with something while you were handling it. (Everywhere, not just at the work site.)

Check on the other side of the board from where you were soldering to see if any SMD devices shifted on their pads. (SMD are those tiny things.)

A magnifying glass and a small flashlight can help big time with some of those above.

Clean up the site after the work with isopropyl alcohol (Rubbing alcohol. I use 91% which has 20% less water than 71% and is just as easy to find.) and an old tooth brush, que-tips, or similar. You want no flux left behind.

If you didn't remove the CMOS battery while you were working you might want to reset the CMOS. (And maybe re-flash the BIOS too.)

Motherboards are thick PCB's. You generally want to use a hot iron (40-60 watts) to minimize the time heat is applied. Warming the site slowly over a long time actually allows the heat to travel further through the PCB than using something very hot and getting it over with quickly.
Also want to use small diameter solder. It takes less time to start flowing and thereby minimizes the time heat is applied.

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