820-00138 PPBUS_G3H 5v after repair to current sense

[Outofwhack]

Board came in dead but I found corrosion over U7100s current sense components C7122, C7120 and C7125.
Replaced those caps and got fanspin.
Connected screen but found during boot power would shut off half way as current draw rose and would then start boot again etc.

Suspected C7120 so removed and could now fully boot.
All well and good but then things get strange.

Thinking I should do the right thing and put a new 47nF cap in place for C7120 and somehow resistance across sense was around 30ohms.
Connected to charger with no fan spin. Then I discover R7121/2 measuring 3 kilohms instead of 10ohms. Burned out?

Replaced R7121/2, resistance across U7100 pins 27,28 a healthy 21ohms or so.
No fan spin and PPBUS_G3H is only 5v

WTF happened? Bamboozled

 

[2informaticos]

C7120 is not even critical; not really needed.
Be sure to have correct resistance between pins 17/18 too.

 

[Outofwhack]

I see 3.2 ohms between pins 17,18 so looks fine.
PPDCIN_G3H_CHGR is 20v and I can see 200khz waves applying then grounding inductor to produce 5v on rhs.
Im seeing 5v on pin 3 from voltage divider although text on schematic suggests it should be 13.55v! ???

 

[2informaticos]

Remove F7140/41 and check C7140 voltage.
Post basic voltage for U7100; 1, 2, 3, 9, 12, 13, 14, 15, 17, 19, 20, 27.

 

[Outofwhack]

C7140 pin1 is 5.3v with fuses removed.
U7100

pin1	CHGR_AGATE	15.2
2	CHGR_DCIN	16.2
3	CHGR_ACIN	0
9	CHGR_AMON	0
12	PP3V42_G3H	3.4
13	CHGR_RST_L	3.4
14	SMC_BC_ACOK	0
15	CHGR_BMON	0
17	CHGR_CSO_N	5
19	VDD	5.5
20	VDDP	5.5
26	CHGR_SGATE	4.2
27	CHGR_CSI_N	4.6

ppdcin_g3h 16.6
ppdcin_inrush 4.6
and I am no longer getting a green light on charge plug

 

[2informaticos]

Check R7110 and C7111.
You may need to change U7100.

 

[Outofwhack]

I just removed all 3 components attached to pin 3 and still seeing 1 ohm to ground so lifting U7100 right now

 

[Outofwhack]

Well Ive got a green light and PPBUS_G3H back to 12.55v and CHGR_ACIN 3.8

Fuses back. Fanspin and drives the screen without shutoff!

Many thanks

 

[Outofwhack]

Ooops spoke too soon.
During every boot as it is increasing current gain it shuts off every time just as it goes through 2 amps draw.
Still shuts off booting with battery disconnected.
Still shuts off in SMC bypass mode.

 

[2informaticos]

Check resistance between pins 17/18 and 27/28 of U7100.

 

[Outofwhack]

Hi, all solved after doing a better job of soldering on the U7100. Thanks for your help.