820-3437 Boot Loop

[rsiesta]

Unit was claimed to be liquid damage, it was cleaned before I got it, no obvious damage.
It starts to boot, runs about 15 seconds with the fan slowly ramping up to full speed and
then it resets and starts over. VCORE present Usb power on a drive but no activity and
no chime. S0 rails present till the reboot. What areas do I need to look at?

 

[aprendiz]

this board do reboot 2 times before chime so, let it be....

 

[rsiesta]

I let it run 10 cycles everyone exactly the same. I timed it and it is even longer cycle then I thought,
It starts out with the fan on low pulling about 700ma, this lasts around 22 seconds, then the
current drops to 480ma and the fan starts ramping up to full speed over about 10 seconds, then
at 38 seconds it resets and starts the cycle again. In case there other anomalies about this board
I don't know yet this test is just the board and fan, wifi card is installed, no SSD and no Battery. I
have a speaker plugged into the dc board.

 

[2informaticos]

Remove also LIO flex and airport card.
Leave MLB with 5 pins DC cable from LIO, no more things connected, nor keyboard/trackpad.
Use the onboard USB to check for activity.
Let see at least if board stays on.

PLT_RESET_L and PLT_RST_BUF_L come high?
You can try new BIOS, just in case...

 

[rsiesta]

I removed flex and airport card, no change.
Drive plugged into onboard usb port,
power light as soon charger connected, never
flashes till goes off when board cycles.

Checking on U2071.


Pin 2, 3.3v PLT_RESET_L
Pin 4, 3.3v PLT_RST_BUF_L

Both stay steady at 3.3v till unit reboots then
go to zero just like drive light for about 3 seconds
when reboots.

I will try bios from donor board.

 

[rsiesta]

New bios fixed it, chime after 2nd reboot. I guess I get to learn
how to reprogram a bios unless anyone has better suggestion.
If I don't have the original bottom plate so any other way to
get a good serial number then try the one on the cover I
do have?

Anyone have experience with buying one for service like this? I know this isn't the correct one for my LB, but they seem to do them all.

https://www.ebay.com/itm/NEW-Bios-E...h-A1466-Early-2015-2017-EMC-2925/192508321914

 

[2informaticos]

Just replace entire Fsys area from your backup (Fsys <--> $SVS)...

 

[rsiesta]

I am starting from scratch... It looks like it is a WSON8 package,
anyone suggest an adapter or how they built one?
Looks like the only ones for sale are around $100, is that the best choice?

From other posts it looks like I can use a EZP2010 programmer, just need a jig to mount the chip in.

 

[2informaticos]

No Title

Easiest way is to use Medusa 2...
Classic way, remove WSON8 chip and solder it on a SOP8-DIP8 adapter.
You need to tap part of SOP8 pads...

 

[rsiesta]

Based on this post https://www.rossmanngroup.com/boards...h-raspberry-pi

Seems to work ok, found clean bios file.