Hello
I'm trying to fix an asus ux31e ultrabook that shows a lot of RAM errors.
The fault happens exactly after the 2GB mark, and then the faulting addresses follow a base-2 pattern.
By the looks of it either one or more of the DRAM chips have broken solder balls, or at leas one of them is faulty.
Worst case - the CPU itself has a bad solder joint, and that's way out of my expertise and available tools.
I assume it's a mechanical problem because the keyboard is very unresponsive and requires quite a lot of pressure to register any key press.
I've got it for free, so worst case I still get a very nice LCD for witch I can find external driver board, a good SSD and some LiPo cells.
The plan is to first try and reflow all 8 of the ram chips: apply some good flux and re-melt the solder.
If that fails I might try getting a new set of RAM chips - or maybe I can try it "rossman style" and rebuild the balls with leaded solder and a lot of flux.
I can play with it as long as I don't damage the board.
The motherboard uses 8 Elpida EDJ4216BASE-DJ-F chips:
https://www.alldatasheet.com/datasheet-pdf/view/458060/ELPIDA/EDJ4216BASE-DJ-F.htmlThose are no longer available at mouser / farnell (only on aliexpress and at a high price).
I think the closest ones are AS4C256M16D3C-12BCN available at mouser:
https://ro.mouser.com/datasheet/2/12/AllianceMemory_4G_DDR3_AS4C256M16D3C_May2020_Rev1_-2301319.pdfThe main difference seems to be the DQUx / DQLx pins placement - all other signals seems to match.
Are there any other parameters I should be aware of ? the replacement chip seems faster than the original one : DDR3-1666 versus DDR3-1333
(I think I should add an extra layer of aluminium foil on the side with the cpu / chipset to protect it as much as possible)
Thanks,
Alexandru