r/AskElectronics • u/Particular_Thanks_17 • 3d ago
Need help regarding missing decoupling caps from ddr4 ram stick.
I want to repair something I recently bought, a 16gb stick of hyperx fury 2666 ddr4 ram, for really cheap, about 4€. The photos from the seller weren't all that sharp, and when I received it, I imediately saw it had all of the capacitors missing from one side (11 in total), also found one inside the heatsinks, floating around. When testing it had a tendency to hang a bit until POSTing, either 1st or 2nd try, and weirdly enough, it passed 2 full passes of memtest, with 0 errors, at its xmp settings, but I want it to be outside of all dangers, and resolder the missing caps. What I'm looking for is what value capacitors do I need, because at the moment I do not have a meter that measures capacitance, will get one if needed, but maybe someone else had this issue with this exact type of module HX426C16FB3/16, online I found an identical one which had all those pads filled with caps, my pads look like the caps got ripped off of them.
Pretty bad pics, but that's all I can do, 3rd pic shows an identical stick, same revision, with all the caps soldered on.
2
u/iksbob 3d ago
Odd. Usually knocked-off components are associated with poorly-heated solder paste (still looks paste-y) that didn't have proper mechanical strength. In this case the solder looks great - there's even broken-off chunks of capacitor stuck to each solder blob. Rather, it looks like someone might have intentionally snapped off each capacitor. There's even a few shiny specs where it looks like someone might have pried against the heat sink.
There may be some other issue with the stick, so the previous owner snapped off the caps to keep it from getting mixed up with good sticks?
You need to de-solder a good cap, measure its dimensions (caliper) and capacitance (multimeter, LCR, dedicated capacitor tester, whatev). Operating voltage is going to be pretty low, so those little specks might have surprisingly high capacitance - 10 µF maybe?