820-00281-A "The big Dog!" ( no image. Boot looping )

[KC Micro Tronix]

I am a virgin with this board. This is my first one!
It switches to 20v Pulls what appears to be booting current but it's not normal and a little high at the end before it drops to zero and loops. The loop takes 15-20 seconds to complete.

I am looking for schematics now. I will be updating this thread in real time as I try to figure out this monster of a board! I have two of these boards in the Drawer that I have scrounged off ebay the past few months. One appears to boot but I have never had a screen or a machine to test them until today!

Wish me luck!


* update
Just got the schematics and Board View from Bad Caps. I'm going in!

 

[KC Micro Tronix]

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[KC Micro Tronix]

My reference board I purchased on eBay which I thought was a booting board because I could see current draw and activity at 20v turns out suffered the exact same fate as this board. Same symptoms and same problem. No display. I also compared thermal signatures and they were exactly the same. No screaming at you hot spots. I have one more board to try then I have to switch to "Brain mode" and drop to schematics. I have never seen one of these working so I really don't know what thermal signatures and values should be.

eBay board #2......
This board gets the 20V but does not boot. After some quick checking I discovered a short on L8000 and after looking at the PCH I see a little brown tear drop. So this one is headed to the rework machine. I just checked and I do have a nozzle that fits this chip! I was able to source these chips and the 90x90 stencil on Aliexpress. They are on the way. They are a little complex to do by hand so I am going to reach out to one of my vendors for a junk board to get the machine profile tested. For all I know these other tow boards could be those junk boards.

So at this point I do not have a working reference board to figure this out.
Guidance Anyone?

 

[KC Micro Tronix]

[No message]

 

[2informaticos]

Did you check USB activity, apart of searching for video?

 

[KC Micro Tronix]

Yes, Fan spin, usb activity, power button functions to turn off and on.
I am digging in deeper now.

I believe the board is functioning. I am getting both the PP3V3_SOSW_LCD and the PP5V_SOSW_LCD signals after a brief wait period of booting. I do not have a test LCD and believe this one could bad. This is not a back light issue as the LCD even with a flash light displays nothing but those signals would not be present unless the CPU was ready for them. Could this be the MUX?