01-29-2022, 06:06 AM
(01-28-2022, 03:02 PM)kk22 Wrote: I'm considering trying out the hardware mod, but the 1.2a mainboard schematic is giving me pause. Under R614 there's a note: "If eMMC IO-Voltage is 1.8V. Mount R401, NC R423."
Only problem is, there is no R423 in the schematic, and it looks like R401 should be mounted anyway (it's present in the schematic and not marked NC). I haven't had time to open up the phone and take a look, but has anyone else looked at this?
I'm not an electrical engineer and just making uneducated guesses, but looking at the schematics and trying to make sense of that note, I think R423 is a typo and is meant to be R403. R401 (and R402) are used for ZQ calibration of the DRAM (on the chip itself) as is R403 (on the A64). Setting the eMMC to 1.8 V is done by connecting VCC-PC to CPVDD (which also powers the DRAM) while setting it to 3.3 V means connecting VCC-PC to DCDC1. My guess is that ZQ calibration somehow depends on that and shouldn't be done via the A64 if VCC-PC is connected to CPVDD, maybe to reduce noise? I really have no understanding of this though, maybe someone else can make more of this information.