orta wrote: ↑
Wed May 09, 2018 12:40 am
thank you, I read the schametic and short R12 R16 R17 R18 R19 R25 , disconnect R24 , but the pi still can not boot
To convert a CM3 to CM3Lite*
("Read note about SDX_VREF limitation):-
Move R10 to R9 (0R)
Move R24 to R25 (33R)
Add R9, R12, R16, R17, R18, R19 (0R)
As the onboard eMMC is still connected to the "external' SD Datalines I suggest that its best to put the onboard eMMC memory into Reset state in the belief that the I/O pads of the onboard eMMC will be held Tri-Stated (High Impedance):-
Repostion R13 (0R) so that the onboard eMMC Reset line is held Low (Reset State) - see attached image:-
https://www.dropbox.com/s/2szzzgk2sipyo ... T.bmp?dl=0
I modified a CM3 as above and a quick test shows its seems to work OK = works as a CM3Lite, but be aware that the onboard eMMC is still physically connected to the external eMMC Bus lines (there is no way to isolate the onboard eMMC without removing it). I suggest that SDX_VREF (Pins 4 & 6 on the CM3 SODIMM connector) should be no higher then 1.8V to prevent damage to the onboard eMMC (which is rated for 1.8V operation).
Its really best to remove U7, the onboard eMMC if you have a BGA rework station (If your skilled then a decent Hotair station and underside pre-heater set around 180DegC to 200DegC works OK).
The CM3 / CM3Lite are manufactured using Lead-Free solder and as we all know LF is just horrid to rework with... Only attempt to rework these modules if you have suitable rework tools and optical systems - the above components are tiny...! You WILL require Micro Rework skills and the suitable tools...