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820-2936 Green Light No Power/Fan - PP5V_S3 and PP18v5_s5 missing

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Hellfiya

Member
820-2936
No visible liquid damage. No prior history available. Came from another shop, found some components knocked off and replaced them(C7981 - CPUVCCIOS0_EN, D5802 – PP18v5_S5_R, and C4520 – SATA_ODD_R2D_C_N)
I get green light, charges battery(amber), smc reset functions. No fan spin or power. Any ideas? 18v5_s5 missing, S3 rails missing. Does 18v5_s5 supply 5v_s3? Or vice versa?
P3v42 = 3.445v
Ppbus g3h = 12.54v
HS_S5_other = 12.54v
SMC_RESET_L = 3.39v
SMC_ADAPTER_EN = 3.42v
Pp18v5_s5/R = 0v
3v3_s5 = 3.3v; _s4 = 3.3v; _s3 = 0v
Pp5v_s5 = 5v; _s3 = 0v
SMC_BC_ACOK_VCC = 3.43v

Any ideas where to start?

EDIT: No PM_SLP_S5_L
 
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dukefawks

Administrator
Check if there are short pulses on 5V_S3, L7260. Best to check with scope as multimeter is slow and will be hard to catch.

51125 getting warm is probably normal if you can feel it with your lips. Usually your finger cannot detect it.
 
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Hellfiya

Member
I didn't detect any spikes with my multi meter, which is usually pretty decent. I have a really old oscilliscope but I don't really know how to use it. Its a tektronix tas 465, ill try to figure it out and update
 
H

Hellfiya

Member
So I think I figured out how to use the oscilloscope, since I am able to get accurate readings on the lines that work. 5v_s3 seems to remain at 0v, i've tried various trigger settings and sec/div
 
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dukefawks

Administrator
While you have the scope out check if there is 32KHz on pin 12 of U2800. Also check voltages on C1802/03.
The knocked off parts are worrying, what else can be missing that you haven't noticed.....
 
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Hellfiya

Member
I actually have a multimeter with hz and it does indeed read 32.77k hz. I wish I knew how to check on my oscilliscope, but mine is a dinosaur. Analog from early 90s I believe.
 
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Hellfiya

Member
Whoops, I got distracted trying to learn to read hz in the oscilloscope, which I did manage. I see 3.29v on each of c1802/3
 
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dukefawks

Administrator
Well, at this point it could be anything. As I said the knocked off parts are worrying as there could be more missing. Possible crap under SMC maybe? More knocked/damaged parts?
 
H

Hellfiya

Member
I just tried replacing the smc from an identical model and same result. Also, thoroughly went through the board a few times to verify no other components are missing. I wish I knew what the other person did with the board. It didn't look like itd been worked on due to the typical dust I see on unworked boards. Guess I'll just put this one asked and try some other testing in the future. Thank you again, Duke!
 
H

Hellfiya

Member
I finally found something significant, q7030 appears to be welded to the board, trying to remove it tomorrow. I haven't been able to find any shorts either. Probably another time-wasting board. Might just use it as a donor seeing that most of it is in good condition.
 
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dukefawks

Administrator
Q7030 would only affect PPBUS. Seeing that is at 12.6V it is not the problem probably. Even if it caused problem the board should still power from a charged battery.
 
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dukefawks

Administrator
It would cause power cycling which can be perceived as no power as the pulsing is hard to catch on most multimeters. Best to use a scope and see if any power is coming on/off quickly.
If the BIOS was not touched I would not really suspect it.
 
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