a1708 - 820-00840 - No Power 20V-0.03A Not stable.

[saisoni20]

Hi,
I have got A1708 has 20v-0.03A (turning ON-OFF) No Power. Input Amp is turning on -off.
I have PPBUS_G3H - 13V.

Voltage is fluctuating at L7030 with input 0 t0 7.8V.

Someone can help me with this?

[mon2]

Remove the fuse on ppbus_g3h and check if the power cycling stops. Is the ppbus_g3h voltage stable without a load?

Remove all power and check the resistance to ground of each inductor on the board. Checking for a lower than normal resistance on the rail.

[saisoni20]

after removing fuse power cycling stops.
ppbus_g3h is stable 13V

indusctor L7900 -PPVCCPCH_S5G and L8060 -PP1V_S5G is showing me 0.3 ohm

[mon2]

The CPU may be shorted but check as follows - remove all power. Meter in lowest resistance mode (if manual meter type).

Place one meter probe on the downstream / consumer side of the fuse PCB pad (fuse should remain off the board). Place the other meter probe onto any of the inductors that is used for the CPU power supply. You are checking the resistance between the PPBUS_G3H rail and the low voltage inductor to confirm if the high side mosfet is leaky or not. What is the measurement? If the resistance is low, then the high side mosfet has leaked and injected a high voltage onto the low voltage CPU and components.

Perform this check with other inductors on the board which also use the same high voltage of PPBUS_G3H to create a lower voltage rail = buck regulator type.

[saisoni20]

They all are 150k between PPBUS_G3H rail.

[saisoni20]

mon2 is it CPU?