820-01814-a

[shlom]

Hello
working on a board 820-01814-a from a1990 machine.

the mac is dead, does not charge or power on..

while checking with usb c measuring tool on the charger
it is drawing 5.17V and 0.01A

took out the logicboard, looks very clean, missing PPbus_G3H
and also missing every other power rail, actually can't seem to find any working power rail...

any advice on how to move forward?
any common issue, missing ppbus_g3h with theses boards is worth checking?

on diode mode i get direct short to ground on PPbus_G3H

i have two in exact same condition \ issue..

please you adsive..

thanks.

 

[2informaticos]

Post the exact ohm resistance to ground on PPBUS_G3H; switch to ohm scale.
Compare with the value on the big coils; pay atention to CPU and GPU coils.

 

[shlom]

PPBUS_G3H is 0.3 ohm to ground.
big coils around cpu and gpu, i hope i understood correctly - measured for exa. on
L7211 - 2.7ohm
L7221 - 2.7ohm
L7231 - 3.0ohm
LA340 - 1.6ohm
LA640 - 1.4ohm
LA650 - 1.4ohm

measured all with black probe to ground

between ppbus_g3h and L7211 there is 2.6ohm

my mistake earier - it wasnt diode mode, just ohm mode with a beep
getting a continuation(beep) between ground and ppbus_g3h and also between ground and L7211

not sure if that how it should be, don't have a good board to compare with

thanks for the help...

 

[2informaticos]

Lift mentioned coils one side (one by one) and check if short disappears from PPBUS_G3H.