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820-3437 powers on no video

J

jgraffis

New member
I'm working on a 820-3437 that powers on no video on internal or external. It does a PRAM reset but does not chime, it also does an SMC rest.

customer states that they plugged a usb drive in and the machine shut off. i could not find liquid damage either.

i checked u8300 and had no voltage on pin 4-5 check to find I'm also missing voltage on pin1. pin 2-3 have 3.3v. r1431 resistance to ground is 0.527.ppvcomp_so_cpu is 1.0v on pin 1 of r0530 pin 2 was .442v.

seems like u0500 is not working fully. Any ideas?
 
D

dukefawks

Administrator
How do you know it does a PRAM reset? Disconnect IO board flat cable to rule out an IO board issue. It will power on without green/orange light. There will of course be no chime as all audio is on the IO board.
 
J

jgraffis

New member
I'm guessing on the pram reset as the machine will turn off then back on while holding the keys down. maybe its not actually doing the reset or not fully? just reporting info. i changed the io board out powers on and runs no video with or without the io cable attached.
 
D

dukefawks

Administrator
Use a known good IO board and cable and see if the chime comes back. Measure data lines of both USB ports on diode mode.
 
J

jgraffis

New member
Does same thing with tested IO board and cable. power on. no chime

on j4600 in diode mode
pin 1 0.456
pin 2 0L
pin 3 0L
pin 5 0.629
pin 6 0.627
pin 8 0.328
pin 9 0.328

on j9500 in diode mode
pin 3 0.435
pin 6 0L
pin 8 0L
pin 23 0.447
pin 36 0.374
pin 38 0.374
pin 44 0.323
pin 42 0.323
 
S

SMMRepair

Member
Try a new WiFi board, just in case. If the WiFi board was liquid-damaged, it can cause this sort of issue. Had 2 several weeks back that powered on to backlight, but no chime or video data, and turned out the wifi card had an issue. Extremely minor corrosion (literally 1 burned/corroded cap), but enough to cause that issue (probably pulling a 5v rail down or something).
 
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dukefawks

Administrator
I have no idea, if this really happened while connecting a USB device I would look there. Measure both data pins on diode mode on both ports.
 
J

jgraffis

New member
its kind of a tough one. i didn't find any short to ground on the usb ports and from what i can tell they both work when i plug in an external with a light on. i am missing EDP_PANEL_PWR. Which makes me thins something is going on with the processor or a component in that line. but didn't think that would make it not chime.
 
D

dukefawks

Administrator
Chime is the first thing you need so you know the board is finishing POST. If you connect a USB HDD can you see activity that it boots from it?
 
J

jgraffis

New member
with usb hdd i do get a solid light, but not any activity like it flashing. Which it normally should do. So i don't believe that it is passing post. I'm not real familiar with the power rails required for post, but it is getting at least some what there as i have the S0 rail working. not sure but don't think that if the surge came from a device that got connected it would cause this. Seems more like the machine didn't like have anything connected to the usb port. i was kinda expecting one of those customers that claims no liquid dmg but really did spill some thing on it, but the board is clean.
 
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