820-00928 No POST

brunomotter

Member
Got this board here for rework. It came here about 2 or 3 months ago for repair... On the occasion it had a short on 3v3 line that was preventing machine to turn on, also some corrosion around U7100, which I cleaned and replaced. Machine worked well for the next 2 or 3 months and yesterday it came back. Machine turns on, get all voltages, no POST. Board alone draws around 1 amp from charger, CPU gets hot and have 0.9V on L7211/21 but no chime. Tried flashing BIOS and verified all termination resistors, all good... Still no POST. Tried replacing U7100 again, same.
 

2informaticos

Administrator
Staff member
CPU core should drop to 0.6V aprox, when board boots; no good if stuck on 0.9V.

I suspect something else affected by corrosion.
Can be a simple resistor, or even bad CPU.
PLT_RST_L goes high?
 

2informaticos

Administrator
Staff member
Then you have a communication problem on some data bus.
If you discarded BIOS for sure, probably bad CPU; if cannot find anything corroded on the MLB.
 

brunomotter

Member
Well, I don't believe CPU is completely dead because a light of hope has brighten here... One time I plugged the board the CPU negotiated 0.6V, so it's alive probably... But after that, I put it back on the case and it never posted anymore, so back to point zero. I even thought it was bad BIOS file because when the board posted it was right after flashing a different file on BIOS chip, but couldn't make it anymore. Probably something has a bad contact and the heat used to solder the chip made it work... Maybe bad PCH solder?
 

2informaticos

Administrator
Staff member
May have accumulated crap under CPU, or PCH; even RAM chips may be affected.

If PCH releases PLT_RST_L, all voltages from MLB should be good.
Now you have a communication problem on some data bus.
 

brunomotter

Member
Well... After leaving board on desk for 1 week, today I decided to start poking on it again... Now it's a little different than before... Board almost all times gives 0.64V on L7211/21 if external monitor connected and internal disconnected, but no chime/video. If internal screen is connected and external disconnected L7211/21 give 0.9V and same no chime/video. Looks like BIOS somehow is communicating with CPU/PCH but something is still missing.
 

2informaticos

Administrator
Staff member
Was saved as clean ME.
But I don't remember when it was created.

Put back BIOS which gave you 0.64V on VCORE and test again.
 
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