820-02020 5v

[Outofwhack]

Im going around in circles not understanding whether Ive got a CD3217 area problem or a U5200 problem.
No corrosion.

Both ports stay at 5volts and draw a fluctuating 0mA to 300mA but no switch to 20v.
I saw some reduced readings on an LDO of one CD3217 and tried replacing it. I replaced both in the end but still no 20v.


I was getting 12.3v on PPBUS_AON but eventually I noticed every few seconds it would dip a couple of volts. See voltage graph.


I removed fuse F5200 and impedance of downstream cct looked fine.
Under no load regulator side of open fuse PPBUS_AON sat steady at 12.3v
I connected a dummy load of 22ohm to see if it could supply roughly 0.5amp. No! Supply sank to 0.2volts
Changed U5200 but still same.
Continuity of PBUS to CHGR_PBUS_SNS (A3) of U5200 good.
CHGR_AUX_DET is 1.28v .
PP1V8_S2 is 0v when fuse removed. VDDIO1P8 on U5200. Does not need 1.8v to produce 12.3v as seen when dummy load removed.

Guidance appreciated

 

[2informaticos]

"PP1V8_S2 is 0v when fuse removed"
Of course, PPBUS_AON is the mother of all secondary power supplies!

If you get steady 12.3V at C5250, when fuse is removed, your problem should be on secondary side.
You didn't say anything about 3V8_AON; diode mode and voltage.

 

[Outofwhack]

Can we not rule out the secondary side downstream of the F5200 ???? since I connected a 22ohm resistance to the steady 12.3v on C5250 [with F5200 removed] and it sank to 0.2volts.
The regulator could not even drive 0.5amp (expected if a 22ohm resistance is used as load on a 12.3 volt supply).