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820-3437 no PM_SLP_S4_L

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Fizzl92

Member
Hello,
i am working on a 820-3437 that is not turning on. Some S3 Rails are missing. I followed this path and the enables and PM_LSP_S4_L are missing. On two sections of the board (U7501 and R5151) i could find some minor sights of corrosion but no damaged Parts/traces there. I attached a picture of U7501. Bios resistors and traces look fine too. Now i am stuck.
Thank you for any help!
 

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dukefawks

Administrator
5V coming on at L7520? If that does not come on it will be power cycling and nothing else will work. Seems like U7501 could be dead or corroded trace/resistor there.
 
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Fizzl92

Member
L7520 has 0.0V on it but no short there. Can there be 5V if P5VS4RS3_EN and PM_SLP_S4_L are not there?. I exchanged U7501 to be sure it is fine and there are no corroded traces. But still no change. On the other side of U7501 PP3V3_S5 is created (3.3V on L7560) so i assume that U7501 is working fine.
 
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Fizzl92

Member
PPVRTC is there. U1900, U1950 and the surrounding areas look fine. i took a close look of the complete board but nothing else is looking bad except for one Ground probe point that was a little corroded... Should i put it in the ultrasonic if i can´t find any visual damage?
 
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dukefawks

Administrator
Sure why not. You did check for power cycling, hard to catch on a multimeter, impossible on an autorange one. Best to use a scope.
 
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dukefawks

Administrator
Make a picture of what U7501 looks like now. Did you check for pulsing on all rails, preferably with a scope. Checked all rails for short to GND?
 
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Fizzl92

Member
No Title

PPBUS_G3H, PPBUS_S5_HS_COMPUTING_ISNS, PPBUS_S5_HS_OTHER_ISNS, PPDCIN_G3H_ISOL, PPDCIN_G3H, PP3V42_G3H, PPVRTC_G3H, PP5V_S5, PP5V_S5, are all there and stable. Other rails are missing because PM_SLP_S4_L is missing.
 

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dukefawks

Administrator
If anything is wrong it will be power cycling. You cannot just say SLP_S4 is missing without checking for power cycling. Hard to catch on many multimeters, impossible on auto ranging ones.
 
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Fizzl92

Member
I got a scope now and checked all present rails for pulsing but i couldn´t find any unsteady rails. So can i say that it is not power cycling or did i do it wrong? But still no 5V on L7520... I´m really confused when PM_SLP_S4_L is missing...
 
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Fizzl92

Member
all resistors measure fine and there are 3-3.3V on all pins (R7202 = 8.58V) so i assume everything is fine there
 
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dukefawks

Administrator
It could be that the 3V or 5V spiked when water hit U7501. Measure resistance to GND on both rails and compare to a good board. Otherwise I am out of ideas besides crap under the SMC.
 
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