820-02890-a 20v present but no ppbus

[kjchatman1]

this board is look similiar to the a2485 logic board. It had a spill in the audio amp area (ur600, ur630 and ur660). the rest of it looks unbothered. f5200 and f5201 are reading 3v. pp3v8_aon is 0v. this is very unusual since 20v is showing the usbc port meter

 

[2informaticos]

Remove F5200/1 and check C5250 voltage.

 

[kjchatman1]

12.4v on pin 1 on c5250. the 20v on the meter is now 5v since i removed f5200/1

 

[kjchatman1]

is voltage injection safe?

 

[2informaticos]

Check ohm resistance between PPBUS_AON and 3V8_AON.

 

[kjchatman1]

62.6k ohm

 

[2informaticos]

If you get correct C5250 voltage, removing F5200/1, the problem is on the system side of PPBUS_AON power rail.
Check for short on all secondary power supplies.

 

[kjchatman1]

is it safe to inject voltage on ppus_aon

 

[2informaticos]

Why???
There is no short!

No reason to inject voltage in this case.
You must check all secondary power supplies.

 

[kjchatman1]

so the short isn't on ppbus but it's on another one that's created with ppbus?

 

[2informaticos]

That is, in theory.
Check first for short between PPBUS_AON and the output of all secondary power supplies connected to PPBUS_AON.

 

[kjchatman1]

what does a short between ppbus_aon and the secondary rail going to look like? will there be very little resistance the two?

 

[2informaticos]

You should check the resistance between both rails; not to ground...

 

[kjchatman1]

what range of resistance would denote a short on that rail

 

[2informaticos]

We talk about a short BETWEEN TWO RAILS; not a short from a rail to ground.
You should get high reading in diode mode and OL in reverse way.

 

[kjchatman1]

one of the secondary rails is shorted to ground? another thing that i first noticed is that the amp meter will continue to reboot with the battery attached

 

[2informaticos]

You may not have any secondary power rail shorted to ground.
But a short between PPBUS_AON and any secondary power rail, will block the board.

 

[kjchatman1]

there is no schematic or boardview for this newer model. the only area corroded was the audio amps. maybe removing ur600/630/660 is the answer?

 

[2informaticos]

Audio amps cause many times problems on main power rails, when affected by corrosion underneath.

 

[kjchatman1]

how is it that 20v shows on the amp meter even thought 3v8_aon isn't there to power the pmu?