820-01700 not booting, 4V PP2V5_NAND_SSD0 but 2.5V when the machine is off.

[xdever]

Hi all,

I got a 820-01700 of a friend that doesn't turn on. I read that a typical issue with these boards is the TPS62180 generating the NAND voltages, so this is where I started looking. Sure enough, PP2V5_NAND_SSD0 is 4V when the machine tries to turn on (I try to determine this by measuring PP2V5_NAND_SSD1, which is 2.5V as it should in this case. The PP0V9_SSD0 and PP1V8_SSD0 power supplies for the SSD are on at the same time when PP2V5_NAND_SSD0 is 4V). The extremely weird thing is that when the machine is off (PP2V5_NAND_SSD1=0, PP0V9_SSD0=0 and PP1V8_SSD0=0), PP2V5_NAND_SSD0 is 2.5V. The TPS62180 looks perfect, the SSDs have no visible sign of damage, I checked with thermal camera and nothing gets hot. PP2V5_NAND_SSD0 measures 0.387V in diode mode (for the good side it's 0.421V, but the good side only have 1 SSD chips, and the bad have 4 of them, so I guess it's kind of right).

I can put the MAC in DFU mode with macvdmtool, but when I start restoring the system, it just disappears from USB and turns off.

Additionally, when the machine tries to start, it power cycles every 20 seconds (all the SSD voltages go away for a moment and then come back).

I know about the special power requirements of these boards. I have the battery connected and I plug in the original 96W adapter.

Does anybody have any idea what could have happened here?

Thank you,
Robert

[mon2]

@ 4V, the PP2V5_NAND_SSD0 is dead. With dead nand, the DFU cannot complete. Crapware design.