820-3435 Pulsing Rails


New member
Hey all :)

Been struggling on for some time now watching videos etc. relieved to have signed up and apologies for any silly questions..

Have an 820-3435 with Pulsing Rails. Green/Orange light, no fan

PP3V42 3.425-3.427
PPBUS_G3H 8.58-8.65 then every say 3-5 seconds drops to 8.25 for a moment

U7100 Measurements
18-19.6 (using an 18.5v charger which is really 20v)
3 - CHGR_ACIN 5.29-5.35
4 - CHGR_VFRQ 3.1-3.3
9 - CHGR_AMON .052-.062
13 - CHGR_RST_L 3.381-3.387
14 -SMC_BC_ACOK 3.387-3.395

SMC bypass no fan

Multimeter batt should be fine and stable readings on other boards, also with same charger.

Board has a fair bit on moisture exposure, lots of tarnished pads but no actual spills.

Help appreciated!
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Staff member
"9 - CHGR_AMON .52-.62"
Too high; measured on charger mode only?
Check exact resistance between pins 27/28 of U7100.


New member
Thanks for the quick replies :) will check VCore tomorrow as home now.
Where best to measure?
PPVCC_S0_CPU pretty sure was 0v
SMC_CPU_VSENSEOUT @ R5520 also pretty sure was 0v

Many test points are tarnished, nothing eaten through. No spills. The usual " Its ever been wet" from customer, seems about 70% honestly didn't see the splash :)
High humidity area and near the ocean here.


New member
Oops.. Late night scribing there. Still higher that usual although much less so. Corrected original post.
9 - CHGR_AMON .052-.062
Will check resistance when back at work, Thanks :)


New member
Hi friend, check out my thread titled 820-0064 need U8080. Your issues sound quite similar to mine. Esp the part about the pulsing PPBUS_G3H. On mine i thought it was U8080 but have found other issues. I was wondering if you could help me too actually and seeing if too the right of your audio codec chip on the DC in/IO board (pin one indicator on the upper left corner) there are some black resistors that measure to ground on both sides. This is so far my closest clue as to what the issue is on mine. Id be happy to take comparison measurements on my board, which although dead have managed to get some life out of it so far.
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New member
Hey mexicoTV
been working on another board as on a deadline to get sorted for customer.
have checked with another DC board (for a 13?, sits sideways although fine for powering on 11? if that?s the only other option.) and all still pulsing so definitely the main board that?s causing the issue.
are you getting VCore at all? Where are you measuring for vcore?
cheers and good luck!


New member
Replaced R7202 as saw a burn dot on it. Burned out again. Replace again with C7202 also, looks like they are both ok now. Still pulsing.

Replaced U7100, no more Pulsing :) PPBUS_G3H starts about 1.5v and drops from there.

Went to another board as on a tight timeframe so quickest solution best. Changed U7100 on that one too. Got same issue with PPBUS_G3H starting about 1.5v and dropping from there.

Figured it may be a bad batch so tried last one from pervious good batch on second board. Stable but G3H 8.17v and no fan. SMC_RESET_L is 3.38v. Tried a SMC reflow no change, dead SMC on that one?

Swapped good U7100 to original board. No pulsing, PPBUS_G3H jumping around between 4 and 5v.

At this stage would love to have some help!

Its 1:30am here in Australia, customer whats in back fixed or not tomorrow. If anyone with more brains and experience is awake out there and wants to lend a hand yay! if not see if I can get to bed before the kids wake up!

Cheers :)


New member
Last cal for help on this one! Maybe I'm not posting the right stuff? Noob apologies..

U7100 Voltage list with new good ISL

Changed fluke batteries in case that was giving my random readings and tried with bench power. very similar stull..

1 - CHGR_AGATE 0.0005
2 - CHGR_DCIN 19.67
3 - CHGR_ACIN 5.334
4 - CHGR_VFRQ 3.327
5 - CHGR_ICOMP 0.214
7 - CHGR_VCOMP 0.722
8 - CHGR_VNEG 0.255
9 - CHGR_AMON 3.966
10 - SMBUS_SMC_5_G3_SDA 3.425-3.427
11 SMBUS_SMC_5_G3_SCL 3.425-3.427
12 - PP3V42_G3H 3.426
13 - CHGR_RST_L 3.390
14 -SMC_BC_ACOK 3.357
15 - CHGR_BMON 0.063
16 - CHGR_BGATE Random .4 to .8
17 - CHGR_CSO_N 3.8 to 4.6 pulsing
18 - CHGR_CSO_P 3.9-4.1 Pulsing
19 - PP5V1_CHGR_VDD 5.010
20 - PP5V1_CHGR_VDD 5.010
21 - CHGR_LGATE 0.033
22 - PGND 0
23 - CHGR_PHASE 4.0-4.1 pulsing
24 - CHGR_UGATE 4.2-4.8 pulsing
25 - CHGR_BOOT 6.4-6.45 pulse
26 - CHGR_SGATE 19.49
27 - CHGR_CSI_N 19.77
28 - CHGR_CSI_P 19.51


New member
Thanks for the reply 2informaticos

I can't find those resistor numbers on the 820-3435 schematic?

Will check traces around U7100.


New member
Checked CHGR_AMON again and reading .030 Must have muted up that reading? Sorry.

Noticed when using Bench power its only pulling .008 amps, orange light on.


Staff member
Does the board start on battery only?

Post exact value (ohm scale) for R7180/81 and R7185/86.

Mea culpa for above; read R712x instead of R702x...