820-2915 power cycling

[arghhh]

820-2915 seems to be power cycling. I get bursts of the S3 and S0 rails. SMC_PM_G2_EN and P3V3S5_EN cycles high-low. Can't find any shorts or heat on the board. PPVRTC_G3H also seems to be cycling, but between 3.3-3.4v only.

 

[dukefawks]

History? PPBUS?

 

[arghhh]

Came from another shop, so not much. Looks clean, no noticeable liquid. PPBUS_G3H is steady 12.5v.

 

[dukefawks]

G2_EN will cycle when S5_PWRGD does not come high, but could be many other things. BIOS, clk chip, too. CPU Vcore coming on?

 

[arghhh]

S5_PWRGD is cycling high-low. I don't get CPU vcore. It's about 7 ohms to ground, doesn't seem like a short but don't have a good board to compare to.

 

[arghhh]

No ALL_SYS_PWRGD, and PP3V3_S0 isn't coming on all the way (less than 1v).

 

[arghhh]

Q7812 doesn't seem to have anything on its gates, but Q7830 does cycle to 0v on its gate.

 

[dukefawks]

3v3_s0 is needed to enable ALL_SYS, check why 3v3_s0 is not coming high.

 

[arghhh]

Beat you to it see above.

 

[dukefawks]

Q7812 doesn't seem to have anything on its gates, but Q7830 does cycle to 0v on its gate.

This is not possible. Q7830 gate can only be pulled low if PM_SLP_S3_R_L is present which goes straight to Q7812 gate.

 

[arghhh]

I know, I thought the same thing but I'm really not getting anything. It's possible that my multimeter is just too slow to pick it up, but I don't have an oscilloscope.

 

[dukefawks]

Well, if you give me measurements that don't make sense there is nothing I can do.