[Q] eMMC crash - possible reasons and solutions
I've been looking around here for some time, reading all that suff about eMMC chips burning on Desire S. That fact dissapoints me as I was aiming to buy the gadget myself.
However, I didn't find any general solution or even investigation of the case, so I'm trying to develop some kinda stuff. Let me summarize main points that we have so far.
1) The faulty guy is usually Samsung eMMC-type BGA chip KLM4G2DE (2 Gb NAND flash), however Sundisk chips were also found to burn.
2) The problem is rather hardware than software dependent as it is observed without any corellation to hboot/flash installed.
3) It was noticed that in many cases eMMC fault followed extraction-insertion of battery after phone freeze.
4) HTC doesn't recognize this as defective case and no improvements to hardware are made in new revisions of motherboard (MB) as there have been cases (at least one) when the same phone after warranty repair crashed again after some time.with the same eMMc chip installed
5) Other phones with the same eMMC installed (e.g. Sensation) doesn't experience same problems.
What can I deduce out of all this stuff and my own experience?
As soons as the case seems to be non-software dependent it should be the chip or some other hardware that drives it wrong. As soons as the chip itself seems to be OK (see 5) I beleive that it is poor motherboard design that burns the chip down. eMMC is rather bomb-proof architecture combining the memory itself and the memory controller on the same crystal. Two major ways to drive it wrong are:
1) Supply incorrect clock pulses to clock bus
2) Supply incorrect power (current/voltage/voltage slope) to memory and/or controller
The first assumption seems not very possible as clock usually comes from centralized source controlled by oscillator. If the clock is wrong, the emmc fault wouldn't be the only problem
The second point seems rather reasonable as Samsung eMMC power-up guide (see file attached) directly points out the importance of accurate power supply (especially power-on slope!), otherwise memory faults are inevitable.
That's all I can deduce so far, unfortunately there's no photos/schematics of desire s on the web to analyze the connection of emcc chip to MB. What can I suggest to prove/disprove all the stuff I wrote:
1) Can someone brave disassemble his Desire S and make high resolution photos of both sides of motherboard? This may help in further analysis.
2) Can someone even more brave and being on close terms with oscilloscope try to measure power-up voltage slope on Vсс and VccQ inputs of eMMC chip(see document attached) ? May be we are just having one of the issues described in the document.
I found the datasheet four our chip, find it attached to this post