820-00850 A1989 MacBook Pro with kernel panic

[sekidata]

This 820-00850 board kernel panics intermittently, especially when the CPU is stressed.

I came to me with an LCD backlight and a fan-related issue, both were fixed. Now, when I run CPU-testing apps like Novabench or TechTool Pro, the machine panics and restarts. I’ve tried SMC and VRAM reset, as well as DFU Revive.

Is there any chance this is not a failing CPU and instead something else on the logic board?

 

[2informaticos]

Save data and try DFU restore.

 

[sekidata]

The DFU Restore proceeded fine, but now I can't install an OS because the machine kernel panics at some time during the installation, every time I try.

 

[2informaticos]

What was the problem causing backlight and fan issue?
Try the installation using external monitor; disconnect internal LCD.

 

[sekidata]

On external display, I managed to install the OS but kernel panics resumed right afterwards with the same CPU:UNKNOWN error.

The machine originally came with no LCD backlight and the right fan blowing continuously. I found LCDBKLT_EN_L was always 12V instead of 8V, which I fixed by replacing the backlight components R8400 and U8400. The fan circuitry had a missing PMW resistor R6052 (knocked off), which I replaced.

 

[2informaticos]

Check for other knocked off components.
If can't find anything, may have a bad CPU.

 

[sekidata]

No such luck. But I noticed that if I unplug the battery, the machine does not kernel panic. Is that because the CPU gets throttled and the faulty core is less likely to be in use?

 

[2informaticos]

Working without battery, or only battery (no charger), CPU will not work to full specs.
Just in case, test with another battery.