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820-3476 doesn't power on

bighead

bighead

New member
Hi,

This board is liquid damaged.

Corrosion around:
- JTAG(I already removed it).
- Backlight IC - removed
- U1900 - changed
- Q5480 - changed

I've green and orange light.

PPBUS_G3H - 12.57V
PP3V3_S5 - 3.3V
P5V1 - 5.1V
PP3V3_SUS - 0V

PM_RSMRST_L - 0V
PM_SYSRST_L - 0V

PPVRTC_G3H to PCH good.
Checked R1300/1/2/3 all seems good.

One weird thing I noticed.
U1900 PCH_CLK32K_RTCX1 goes extremly high around 3.3-3.6V.
I can see the wave form. However not that nice like on different boards.

I replaced SMC I thought that cause the PM_SYSRST_L not going high.
There is no short on this line. Dead PCH?

Thank you.
 
Last edited:
bighead

bighead

New member
Voltage on Y1905 is 1.16V for a millisecond. No oscillation.
U1900 was pulled from donor board. The original U1900 did the same thing after reflow.
The reason I changed it was this.

I can see the waveform on Y5110 for a sec, but nothing on Y1905.
 
bighead

bighead

New member
Yes, it's steady 32kHz. I changed U1900 one more time from another donor board. Nothing changed.
 
D

dukefawks

Administrator
The fact that there is voltage on Y1905 means the machine is power cycling. The usual suspects apply: U6100 and resistors in the data lines, pin 8 U1950 corrosion? Picture of U6100 area would also help.
 
D

dukefawks

Administrator
I see some crummy resistors around the SMC. Soldering on U1900 looks a bit crappy too.....Must be more corrosion somewhere else.
 
bighead

bighead

New member
Bad looking resistors are replaced around SMC. No change.
Should I pull the SMC and try another one?

Only corrosion was around those components I mentioned in my first post.
 
D

dukefawks

Administrator
Pull SMC and try another one. But before you put the new SMC on pull U6100 and measure all pins on diode mode. Then after you put SMC on measure them again, then put U6100 back. Note all the values.
 
bighead

bighead

New member
Without and with SMC the numbers are almost the same.

U6100:
Without SMC

Pin 1 0.455
Pin 2 0.455
Pin 3 1.1
Pin 4 0
Pin 5 0.469
Pin 6 0.467
Pin 7 0.438
Pin 8 0.392

With SMC

Pin 1 0.452
Pin 2 0.452
Pin 3 1.1
Pin 4 0
Pin 5 0.467
Pin 6 0.464
Pin 7 0.436
Pin 8 0.390

The same problem with another SMC from the same donor board.
 
bighead

bighead

New member
I know it's hard to catch with multimeter. There is nothing neither on the scope.
There is something on Y1905 for a sec when I first attach the adapter, but that's it.
 
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