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820-3435, Green light, No PM_SLP_S5_L.

S

SMMRepair

Member
Posting all of my "tough" boards here recently, and I'm fairly certain most of them have bad CPUs, but want to confirm before placing them into the parts pile. :)

Working on an 820-3435 that received power, gives a good light, and the fan "twitches", so I thought I had a quarter fan spin issue, but all current sensing looks and measures fine. Charger light does not blink or pulse between spins. Checked current sensing, all seems in order. Checked 6259, checks out fine. This board had visible signs of someone goofing with the SPI ROM chip, so I loaded my known-good dump to be sure, but no change. I have 3.3v on all pins for the SPI ROM (except pin 4 of course). I have all my S5 rails and vrtc_g3h. No shorts detected on any of the S5 or mains rails.

Following the block diagram from the 820-3208 (and converting/tracing components and signals where necessary), I do get 1.05v on pin 1 of U7840, but I get no PM_SLP_S5_L, however PM_SLP_S5_L DOES spike when the fan twitches, but then immediately goes back to 0v. It spikes for a split second--too fast for my multimeter to even measure--and then back to 0v. Everything stops at R8115. No heat from CPU or SMC (or anywhere else on the board). Diode on pin 1 of R8115 is .415.

Bad CPU?
 
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dukefawks

Administrator
Must be an issue with SPI data lines then. There are 12 resistors in total that need to be checked and also the traces! Check schematic around U6100
 
S

SMMRepair

Member
Just went through and checked all resistors (18 total) and continuity between all, and all is well. Could the issue be a damaged BIOS chip or corrupt file? I loaded a known-good/clean file (again, to get at least a delayed chime boot, just so I could force update the EFI later to resolve the inevitable ME region issues), but can't get the board to stay on.

Also worth noting: voltage at pin 1 of R6112 and R6111 DROPS to 0v when the fan cycles (along with the vcore drop), but voltage at pin 1 of R6110 and R6113 and stays at 3.3v--no drop.
 
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