820-00165-A, green/orange light but no spin-up

[jpadie]

I've got a liquid damaged (but pre-cleaned) 820-00165A that isn't spinning up. The liquid damage _appears_ to have been pooling around the edge of the board with some residual grubbiness around the SMC and the RAM chips.

The G3H rails are present and the green->orange charger light is as normal.

An oddity is that PPVRTC_G3H oscillates between 3.3 and 3.42v.

The PPV5_S5 rail is present but again it oscillates. This time between 3.6 and 5v.

no other power rails are active.

on U7501 I'm getting lows on EN and EN1 and on EN2 I'm getting an oscillating 0-3v.

any ideas of where to hunt please?

thanks
justin

 

[JohnB8812]

Replace U1900 and see if it fixes the problem VRTC should be 3.3 steady.
If it does not, next places to check would be U1950 pin 8, the SPI ROM traces and termination resistors and the JTAG. But you need to steady out the clock voltage first

 

[dukefawks]

First thing is to find out where the pulsing is coming from. Is PPBUS even stable at 8.6V?

 

[jpadie]

Yes. The 8.6 and 3.42 rails are rock solid.

The signals to the dual mosfet gate are pulsing too, although the lower gate is only oscillating between 0-200mV.

 

[jpadie]

I don't have a spare clock chip but I'm not sure that the rtc is not ok . Pin 8 on u1950 is pp3v42 which is stable. I will check the spi bus but again - this feels like a different kind of issue on the S5 5v regulator circuit. Like a diode failing as a cap discharges perhaps.