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820-3476-a Black screen fan spins high

T

TBFix

Member
I have 820-476-a board . It powers up to black screen , fan spins fast and consumes .480ma - 500ma.
There is no 5v on lcd connector with or with screen attached.
No Enable signal on U8300 (checked for shorts)
U8330 and resistors checked (no EDP Panel PWR)
All S0 line seem to be present
ppbus_g3h is 12.6v
PPVCC_S0_CPU is 1.75v

What are the required conditions for EDP_PANEL_PWR to be present?.
Thanks for the input
 
2informaticos

2informaticos

Administrator
Staff member
Check first if has USB activity; maybe board is completely stuck.
All the people always looks for video only :(

Try known good BIOS...
 
T

TBFix

Member
Have you a link for bios. Also I have checked all the voltages for missing lines so not just at the lcd cable, thats just the signal/voltage I cannot find

usb device has power and activity
 
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2informaticos

2informaticos

Administrator
Staff member
If you have USB activity for sure, do first few PRAM resets.
Also test external video.

L8300 should get voltage in the first few seconds (at chime usually), staying high for aprox 5s; even without LCD connected.
 
T

TBFix

Member
Ok will try that...

edit.. No external video. And tried pram rest but still the same. No voltage on L8300 even from power on.

U8330 ha sonly voltage on pin8 = 3.3v. No shorts.
 
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T

TBFix

Member
I have searched and I cannot find a similar issue to mine with similar readings as all rails seem to be present.

I got a verified bios files from another source but behavior is still the same.

Thanks for your input and assistance.
 
2informaticos

2informaticos

Administrator
Staff member
Can you confirm USB activity 100%???
Use OSX pendrive with Link LED.
You are probably wasting time searching for video into non-working board...
 
T

TBFix

Member
Hi I need to apologies it seems like Im getting power to the Usb ports but no data activity. I have tried with a bootable usb but no flashing leds.
 
2informaticos

2informaticos

Administrator
Staff member
This looks like CPU issue.
But could be just a simple corroded resistor on its area.
Any history fault available?
 
T

TBFix

Member
When I got it the previous tech had removed the bios and messed up the resistors around it so I replaced the missing ones and then got the fan spin and where we are now. I have gone over the cpu area with microscope and cant see anything missing.
What I did found was the diode reading on c7601 on the bad board is 0.0119 and another board 0.143. edit .. with U7600 removed C7601 reads 0.0098
Also what is the relevance to usb activity? what does it tell us?.
 
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T

TBFix

Member
Ok so this board is not having usb activity but has vcore and pch voltage etc and cpu gets very very hot. Would you suspect bad pch ? as i have pretty much tried everything and impedance on the pp1v05_s0 line is lower that good board sa mentioned before.
 
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