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820-00923-A Not Powering Up After BIOS Flash

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imperialboard89

New member
Hello everyone,

I have a 820-00923-A board that used to boot without any issues before I flashed the BIOS. After programming the BIOS chip with the CH341A programmer, the board did not power up anymore.

So, I took the schematics of the board and started checking the power aliases. I verified all the voltages, and they are all correct. The only skewed voltage is on PPVCC_S0_CPU, where the measured value is 0.785V instead of 1.5V. I thought the CPU might be dead, but I'm not certain.

When I try to power on the board, I notice that it correctly receives 20V input, but only draws 0.461A. Using the thermal camera, I observe that the CPU heats up, and just above the CPU, there are the U7210, U7220, U7410, U7420, U7430 chips, all heating up beyond 45 degrees.

I have tested L7210 and L7220, and on both, I read a voltage of 0.785V.
 
2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

You get even S0 voltages, so board powers up; not booting is another problem.
CPU core should drop near the 0.65V when board really boots.
Monitor its voltage from start and see when stops to 0.785V.
Just in case, check USB activity and Caps Lock LED reaction.

I recommend to check for knocked off components near the BIOS chip; be sure U6100 has good solders.
Where did you get the BIOS file?

"board that used to boot without any issues before I flashed the BIOS"
Why did it???

820-00923 tested.BIN

drive.google.com
 
I

imperialboard89

New member
2informaticos said:
First of all, welcome to the forum!

You get even S0 voltages, so board powers up; not booting is another problem.
CPU core should drop near the 0.65V when board really boots.
Monitor its voltage from start and see when stops to 0.785V.
Just in case, check USB activity and Caps Lock LED reaction.

I recommend to check for knocked off components near the BIOS chip; be sure U6100 has good solders.
Where did you get the BIOS file?

"board that used to boot without any issues before I flashed the BIOS"
Why did it???

820-00923 tested.BIN

drive.google.com
Click to expand...
Thanks for the help,

I don't have the green LED on the Caps Lock, but the fans spin at maximum speed. After about a minute, they restart and continue this cycle indefinitely.

Here are the voltages on the following lines:

CPUCORE_PWM1: 0.369V
CPUCORE1_GL0: 4.686V
CPUCORE2_GL0: 4.694V

Measuring the voltage of PPVCC_S0_CPU on C10G1, I get exactly 0.784V after 10 seconds, and after about 12 seconds, the voltage drops back to 0. It repeats this cycle continuously.

I got the bin file on alisaler.com. I had to flash the bios cause I could not install anyone MacOS outside of Sonoma with OpenCore, but the TouchBar was not working with that OS, so I had to solve the corrupted bios issue...
 
2informaticos

2informaticos

Administrator
Staff member
"I get exactly 0.784V after 10 seconds"
I said to monitor the voltage.
Connect multimeter before applying power; see the voltage changes in time!

Did you make BIOS backup?
If not, try the uploaded file.

What didn't work under Ventura, to need Sonoma???

BTW, do not quote an entire post visible few centimeters above.
Write directly on the bottom reply box, instead of clicking reply button.
Please, maintain forum aesthetic...
 
I

imperialboard89

New member
No, unfortunately, I forgot to back up the BIOS.

I've tested Ventura, High Sierra, Monterey, Big Sur, Catalina, but despite everything, I received the message that it's not possible to update after installing the operating system. So, the system never started.

I ask for your forgiveness, but I'm still a beginner, trying to do my best.
I monitored the voltage on PPVCC_S0_CPU, and it starts rising from 0 to 0.785V instantly as soon as the board reaches a current draw of 0.488A. After about ten seconds, the board stops drawing amperes, then starts rising again to 0.488A, and the voltage on PPVCC_S0_CPU remains fixed at 0.785V for the time that I monitored it for about ten minutes, then I powered off the board.

Do you think that if I replace U7210 and U7220 could I solve the problem? I thought at this because the input Voltage on the chips is right, but when I test the voltage on the inductors L7210 and L7220 it is not 1.5V but 0.785V.

I want to clarify that I am conducting the test only on the board, without connecting fans or a keyboard.
 
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2informaticos

2informaticos

Administrator
Staff member
Don't touch anything more, apart of BIOS chip.

Did you flash the file linked for you?

If you make the installation from USB, connect the mac to Internet also.
Touchbar update requires Internet connection.
 
I

imperialboard89

New member
Yes, I flashed the bin file you linked.

Now, after soldering the chip back onto the motherboard, I reassembled the board in the case.
Upon powering it on, I noticed the fans start spinning, the voltage remains at 20V, while the current rises and stops at 2.840A (See here).
However, upon turning it on, I still don't have the green light on the caps lock, and I see nothing on the screen.

Now, I observe that on PPVCC_S0_CPU, I have a value of 1.020V, but I still have the short on C10G1.
 
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2informaticos

2informaticos

Administrator
Staff member
1-1.15V is a good start voltage for CPU core.
But should drop until 0.65V aprox, when board really boots.
Check all SPI Bus Termination resistors, or other components which you could blew up when heating U6100.
Too much heat applied could also affected CPU, or other something else on the board.

You don't need to mount the board in housing every time for test.
I was hoping that you already understood CPU core level after 10-15s is a good enough test; with board alone on the desk.

You don't have any short there.
Don't make wrong assumptions so easy.
 
I

imperialboard89

New member
I've now tested the board directly on the bench. The board draws 0.980A, and the voltage on PPVCC_S0_CPU is 1.15V. However, after just 10-12 seconds, the board starts drawing 0.488A, and the voltage on PPVCC_S0_CPU returns to 0.65V.
I tested also VCC on U6101 and on U6100 and there are 3.3V. (See here)
I tested C6000, C6101 and C6102 and there is 3.3V.

I've tested all SPI Bus Series Termination resistors (these), and they are working correctly.

Is there any other test I can perform?
 
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2informaticos

2informaticos

Administrator
Staff member
"PPVCC_S0_CPU returns to 0.65V"
Looks like board boots then.
You can test external video, or USB activity; board still alone on the desk.
 
I

imperialboard89

New member
I tried external video via display port and via HDMI for both does not work.
USB activity works because I connected a keyboard with backlight ant it works.
Is there something else I can test?
 
I

imperialboard89

New member
I did, but it does show nothing on the screen.

Now I noticed that for the second time the LB190 blow up (See here). I don't know why it has to happen.

I still don't know which test could I try...

Any idea?
 
I

imperialboard89

New member
If I were to power the PPVCC_S0_CPU line using the bench power supply to detect any shorted components with a thermal camera, do you think it would cause any damage? Or could it be a potential solution?
 
2informaticos

2informaticos

Administrator
Staff member
Why do you insist about short there???
Didn't was curiuos enough to compare with good board?
CPU core for such processor shows 1-2 ohm as normal resistance to ground.
You've got even correct voltage there; how possible with short???
 
I

imperialboard89

New member
@2informaticos

Apologies for the delayed response; the holidays kept me busy.

Returning to the issue: unfortunately, I don't have an identical and functioning board to compare values. After checking the main lines and confirming their functionality, I also ruled out an issue with the internal display by connecting an external display via USB-C with both display port and HDMI. However, there was still no display.

Considering a potential problem with the graphics interface, I measured the input voltages to Chips U7410, U7420, U7430. Both VCC and PVCC measured 5V and 13.06V, respectively. The issue arises with Vout, which reads 0V instead of the expected 0.55V - 1.5V range. This leads me to believe that without proper power, it can't supply the graphics part of the processor. (See here)

I also checked inductors L7410, L7420, L7430, and on all three, I read 0V on both ends. What could this indicate?
 
2informaticos

2informaticos

Administrator
Staff member
"I also checked inductors L7410, L7420, L7430, and on all three, I read 0V on both ends."
That is normal; only get voltage there when iGPU detects high load graphics.
But you should get GPU voltage instead, all the time.

"PPVCC_S0_CPU returns to 0.65V"
Is that still valid???
Only then the board boots.
 
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