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820-3115-B no green light, PPBUS_G3H 12.3V

Atomrepair

Atomrepair

Member
This board has had some liquid damage on it, sticky crap but not much corrosion.
No or a dim green light, wont power on.

PPBUS_G3H is 12.3V
PP3V42_G3H is 3.42V
PP5V_S3 is 0 V. Resistance to ground ~22k

SMC_BCACOK is fluctuating between 3.0 and 3.3V. not steady.
SMC_RESET_L is 3.42V

already done:
Fluxed up and heating the SMC to pre-reflow temp. no change
Fluxed and reflowed SMC. still the same deal.

I'm thinking that next on the list may be replacing the SMC, but I'd like to be a bit more sure of that before going there.
 
TCRScircuit

TCRScircuit

Super Moderator
Staff member
Replace U7000. It is PPBUS G3H buck controller and sends out BCACOK. PPBUS is low so may be an SMC but let's try the ISL first.
 
Atomrepair

Atomrepair

Member
U7000 replaced. I've checked everything on BC_ACOK / CHGR_ACOK. R5087 is 470k as it should be. I've lifted U6901 to see if that was mucking it up, but BCACOK stays the same with it removed.

However, I just noticed that PPCHGR_DCIN is fluctuating as well. Its sitting at 16.7V most of the time, but sometimes dips down to 16.0V for a moment. This carries all the way to PP18V5_DCIN, where I get 17.1V dropping down to 16.5 every 10 seconds or so.

note: I've already tried swapping the DC in board and the charger.
 
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Atomrepair

Atomrepair

Member
I've replaced the SMC. Green light went on, machine powered on with fan spinning continuously but no image on screen and no blacklight.
Now that I've had it on and off a few times, it no longer powers on. Instead, it takes 20 seconds or longer for the green light to come on, but its not steady. Keeps on blinking.
Did I botch the SMC replacement or might something else be wrong?

edit - it still powers up right away from another charger.

PPBUS_G3H still 12.3
PP3V42_G3H - 3.45
PP5V_S3 - 5.05V

no gong (right or left speaker attached), no image on external screen.

LCD_IG_PWR_EN is at 0V, but no short to ground. (90k). But I'm guessing I need the gong before looking at the LCD, right?
 
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A

aprendiz

Moderator
12.3V on PPBUS_G3H could be a bad SMC or ISL, also could be a bad soldering on the SMC when it was replaced... CPU Vcore present???? Any activity on USB???
 
Atomrepair

Atomrepair

Member
I'm guessing cpu core being ok or not is this one:
CPUIMVP_VR_ON 3,29V

I've replaced the ISL already. checked a couple of things:
PPCHGR_DCIN16,4V
CHGR_ACIN4V
SMBUS_CHGR_SDAhmm
SMBUS_CHGR_SCL3,46V
CHGR_RST_L3,42V
CHGR_ACOK3,27V
PP5V1_CHGR_VDD5V
PP5V1_CHGR_VDDP5V

I checked SMBUS_CHGR_SDA on the scope. It looks different when compared to a functional 820-2936-B I had lying around. Should be similar, I'd think.

smbus_chgr_sda-820-3115-bad.jpg

SMBUS_CHGR_SDA on 820-3115 with PPBUS_G3H at 12.3

smbus_chgr_sda-820-2936-ok.jpg

SMBUS_CHGR_SDA on 820-2936 which boots into OS (but is very slow)

Thats a bidirectional line, but perhaps someone has seen this before and knows whether the most likely suspect is ISL or SMC..

What do you want me to check when you say activity on USB?
 
Atomrepair

Atomrepair

Member
I decided to spend some time looking through the schematic in the hopes of gaining some understanding.
This isn't really relevant to this particular board, but bear with me..

I see PPVCORE_S0_CPU_PH1 found at L7510 comes from Q7510, which requires input on the following pins to generate PPVCORE_S0_CPU_PH1_L:
PPVIN_S0_CPUIMVP
CPUIMVP_BOOT1
CPUIMVP_PHASE1
CPUIMVP_LGATE1

PPVIN_S0_CPUIMVP comes from PP1V05_S0
The other three inputs all come from U7400

U7400 deals in CPUIMVP and other CPU related stuff and has a bunch of pins it wants to see something on. Those inputs are several power rails, a bunch of lines from the CPU and a couple from (or at least related to) Q7510 and Q7560, which are part of the phased power supply to the CPU. Did I miss anytihng so far?
Am I correct in saying that measuring L7510 or L7520 lets me see whether U7400 and the CPU are working?
 
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