820-3437-b

jgraffis

New member
I've got this 820-3437b that is not powering on. it did have very minor signs of water damage. i check around to find that i had some missing and low voltage on a few power rails.
pp5v_s4rs3 0.0
pp5v_s0 0.0
pp3v3_s4 .041v
pp3v3_s3 .080v
pp3v3_s0 .060v
pp3v3_s4sw_sns .041v

not really sure where to start from here. I think maybe and issue with u8050?
 

jgraffis

New member
sorry i should have mention those as well. ppbus_g3h is 8.6v and pp3v3_s5 is 3.3v. smc_reset_L is at 3.34v at r5100 but no voltage at r7100.
 

jgraffis

New member
liquid damage was on r7520,r7521,r7523 as well as r8164. i check those for the correct resistance all measured good. No voltage on L7520 and y1905 pin1 is 0.003v pin2 0.0v pin3 pulsing from 0.160v to 0.189v, pin4 0.0v
 

dukefawks

Administrator
Anything happening on R7551? Check carefully it may be short pulse after start only. Checked U6100 area for corrosion? U1950 pin8?
 

jgraffis

New member
R7551 does spike to different voltages( tested 4 times highest 1.3v- lowest 0.028v) as soon as i plug in power. no corrosion on or around u6100 even on the test points. u1950 pin8 3.42v.
 

dukefawks

Administrator
It is power cycling then. Could be caused by many things, but the usual are Corrosion in U6100 area, corroded pin on U1950 or the clock chip. Look at the recent video Louis posted about the board from the forum.
U1950 pin 8 can have 3.4V but check under microscope for corrosion. In the video you can see the resistor and traces that usually get damaged.
 

jgraffis

New member
its strange for sure... i get no fan spin, no chime, no video/backlight. what i did find strange was the corrosion i did find ( with microscope) was in those 2 random places, which kinda makes me think some one either cleaned it first or the liquid didn't settle on u6100 or u1950 but the may have still have been damaged.

is U6100 a chip i could pull off a donor to check?

i did watch that video actually just before i started working on that board, and was extremely careful to check the resistors/traces and probe points around the u6100 all seem to be just fine.

so maybe i should try to change u6100 and/or u1950?
 

jgraffis

New member
No Title

under the microscope it looks perfect. not sure if the photo attached will be that great compared, but maybe im missing something.
 

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dukefawks

Administrator
You can check if 5V will come on by removing R7551 and connecting EN1 to R7552 (EN2). As the liquid was in that area maybe something up with U7501
 

dukefawks

Administrator
No, it just proves U7501 is ok put everything back like it was. I have no further clues besides you have to find the corroded part/trace. The machine is power cycling and the normal suspects look ok.
 
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