820-3437, Boots, No Chime/Video, Likely BIOS Issue?

SMMRepair

Member
Another board from my "tough" pile. This board has good green/orange light, powers on, all rails present (including vcore @ 1.76v), but it has no chime and no video. I thought it might be a BIOS/SPI ROM issue, and I noticed that I get 3.3v on pins 1, 2, 3, 7 and 8 of U6100, but not on pin 5 (SPI_MLB_MOSI) or 6 (SPI_MLB_CLK). I actually don't have a working board to compare values, but I believe those should be 3.3v, correct? I actually tried 3 known-good dumps from other boards of the exact same model (2014, 1.4, 4GB) without luck. Same exact issue, so I don't think the BIOS is communicating properly with the PCH.

I get 0v at R6111 pin 1, R6112 pin 1, R6115 pin 1, and R6116 pin 1. All resistors in this circuit measure properly.

All other voltages present and look good. PCH gets appropriately warm. Any ideas here? All help appreciated.
 

dukefawks

Administrator
Have you removed J6100? Also I hope you saved the original BIOS file, you cannot just swap them around without ME region issues.
 

SMMRepair

Member
Correct, I save all BIOS files. This one did not work with the original file, a cleaned ME region original file, a known-good/clean ME Region blank serial file, known-good/clean ME region with original serial and board number applied, etc. I get no progress (no delayed chime, nothing) from any of the files I tried. Even if I can get to a delayed chime boot, I can force update the EFI to resolve. I can't even get that far on this board, though, just a fan. No chime, etc.

J6100 has not been removed, and is clean (no liquid/corrosion).
 

dukefawks

Administrator
If you remove the ROM totally the board should power cycle. Also with chip removed you can check diode mode on all pins.
 

SMMRepair

Member
With SPI ROM chip removed, I get the slightest fan twitch ever, roughly every 5 seconds. Fan does not fully spin and doesn't give the cycle (on/off/on/off) normally seen with missing BIOS.

Diode readings for U6100 with chip removed:

Pin 1: .420
Pin 2: .408
Pin 3: 1.036
Pin 4: 0
Pin 5: .442
Pin 6: .444
Pin 7: .402
Pin 8: .348
 

dukefawks

Administrator
PCH is seeing the ROM then. It could be the SMC is not seeing the ROM because of corroded trace/resistor. Especially pin 5 and 6 look a bit high, so check if those make it to the SMC
 

SMMRepair

Member
Thanks for all the help, dukefawks. I'll probably set this one aside and come back to it when I have time to remove/replace the SMC after checking for continuity. I didn't want to just leave the thread unbumped, and will post back once I have a chance to remove the SMC and check to see if that's the cause. :)
 

SMMRepair

Member
Ahhh, ok. I'll do that this afternoon, then. What value should I expect if the SMC is continuous with the data lines? I guess I could test a known-good board, but just curious of what would be a "good" reading, and what would be "bad". I guess anything low is bad (no load)?
 
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