[SOLVED]820-3787 unstable S5 enables

[G.Beard]

I have no idea what you are trying to do

Yeah, that would be a fair comment.

you check PP3V3SUS_EN comes high? If yes it should pull the gate of Q8020 to pretty much 0V.

PP3V3SUS_EN only shows up if Q8002 is removed. When Q8002 is on the board the voltage at Q8002 gate changes by a couple hunded millivolts and Q8020 gate goes high low high low.

 

[G.Beard]

What should I be testing as the cause of this on off S5 rail problem do you think?

 

[dukefawks]

You didn't answer the question from post #17. The board is power cycling and I bet all S0 busses are coming high for a second. Check closer.

 

[G.Beard]

You didn't answer the question from post #17. The board is power cycling and I bet all S0 busses are coming high for a second. Check closer.

PP5V_S0 = 217mV
3.7k to ground

PP3V3_S0 = 200mV
9.2k to ground

 

[dukefawks]

Are they pulsing? Most multimeters are too slow to catch it, better to use a scope.

 

[G.Beard]

Are they pulsing? Most multimeters are too slow to catch it, better to use a scope.

They are indeed pulsing.

PP3V3_S0 by ~ 2.5V
PP5V_S0 by ~ 500mV

 

[dukefawks]

Is CPU Vcore pulsing too? Check all coils for shorts.

 

[G.Beard]

Is CPU Vcore pulsing too? Check all coils for shorts.

No voltage on vcore at all, not even a spike on the scope.

Diode DMM
L7310, L7320, L7330, L9360, L9330 = 0.005V drop to ground
L7520 = 0.000

 

[dukefawks]

Uhm, there is a short to GND on L7520? That is at least one problem to fix first. Inject some voltage and see what heats up.

 

[G.Beard]

Wow, what a prize fucking moron I am... Ahh jeez. Yes, clearly short to ground but I spent ages searching for the problem going through the schematic around in circles and you say, test S0 rails, check for a short, throw in some watts and see what burns your fingers.... And it's fixed! Thanks for sticking with me.

It was a cap USB switch.