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820-01061 BIOS

brunomotter

brunomotter

Member
Hello. Does anyone have this BIOS file here? I got a board from this iMac here that boots when it wants. Most times it get stuck on apple logo screen without loading bar under it, just apple logo, nothing else. Tried new SSD, new RAM, disconnected webcam, pulled off airport card, disconnected headphone jack, tried even new PSU and tried booting with known good OS from USB. Same results. It get stuck on apple logo. Sometimes(rarely, after forcing it turn off and on again) it boots and when it boots everything works perfectly until I restart or shut down the machine. I'm suspecting BIOS because in verbose mode it gets stuck right before start loading OS like if it's a bootloader problem.
 
brunomotter

brunomotter

Member
Seems this file is bad... Anyway, seems the machine responded somehow. It acted differently at least in the beginning. As soon as I put the file in the chip I could reset PRAM, and the machine was responding the OPTION key for entering boot menu. But I think ME is bad on this file because it says something about ME on verbose mode and hangs for a looooong time on this message before it boots. When it boots it stays for about a minute and when it's finishing loading OS services the machine crashes and gives a KP. I tried reinstalling a fresh copy of Monterey to see if somehow it updated the EFI and corrected the problem but after the first reboot on install it got hang on apple logo again as it was before flashing BIOS. I made a copy of the original file and will post here to see if it helps. If you have medusa and could clean ME for me it would be great! Thanks in advance.

BIOS Original Samuel.Bin

drive.google.com drive.google.com
 
brunomotter

brunomotter

Member
Hello. No chance! It's not just BIOS. No corrosion on any points of the board, everything is clean. Maybe bad CPU, but as I don't have one to test, no way to tell
 
brunomotter

brunomotter

Member
I think I found the culprit of the problem. It's related to USB-C ports. One of the 2 controllers looks burned. I replaced it and the board worked well until I plugged in an external HDD to one of the USB-C ports. Then the machine went crazy again. I took the board off the chassis to inspect and the same controller burned again on the same point of the previous one. I'm stuck now as I cannot find any shorts. Seems something that happens only when something is connected to USB-C port
 
2informaticos

2informaticos

Administrator
Staff member
When external device is detected on the USB-C input, machine will sends out 5V on the VBUS line of that port; in case of pendrive, or external HDD.
Check diode mode to ground on the terminals of USB-C ports.
 
brunomotter

brunomotter

Member
I found out that one of the USB-C ports ir shorted on one side. I removed an R0 resistor that goes to power of the CD3215 and discovered the short is from CD3215 side and not port side. As I don't have schematics I cannot proceed on repair because I need to know what components belong to that particular line and injecting 1V on it draws full 5 amps from my bench PSU and nothing gets hot. I believe either on a shorted cap on line or the USB-C/Thunderbolt controller. With resistor removed from board the machine works fine but with that particular port disabled of course. How could I try to discover what's shorted? I know it's not the CD3215 as I took it from a donor board with bad CPU but that had working CD3215.
 
2informaticos

2informaticos

Administrator
Staff member
Inspect USB-C terminals.
Also, each line has diode protector, which can get short.

820-00597 schematic may help you.
 
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