MacBook Air 13"
820-3209-A
Board Specifications
| Parameter | Value |
|---|---|
| Board Number | 820-3209-A |
| Apple Model | MacBook Air 13" Mid-2012 (A1466) |
| CPU | Intel Core i5-3427U / i7-3667U (Ivy Bridge, BGA1023) |
| GPU | Intel HD Graphics 4000 (integrated) |
| RAM | 4GB/8GB DDR3L-1600 soldered (dual channel) |
| PCH | Intel Panther Point HM75 |
| SMC | U5010 — SMC_BC_ACOK, PM signals |
| Charger IC | U7000 — ISL6259AHRTZ |
| Schematic Pages | 109 pages (J13 revision) |
| BoardView | Available (.brd format) |
Known Issues: This board is highly susceptible to liquid damage around the CPU VCore regulator (U7100 area) and the isl6259/" class="comp-ref" title="ISL6259 component reference">ISL6259 charger IC. The TPS51125 (U7200) 5V/3.3V supply is a common failure point after liquid exposure.
Voltage Rails Reference
| Rail | Voltage | State | Regulator | Page | Notes |
|---|---|---|---|---|---|
| PP18V5_DCIN | 18.5V | G3H | DC-In MagSafe | 69 | Direct from charger. If absent: check MagSafe connector pins, fuse F7000 |
| PPBUS_G3H | 12.55–12.8V | G3H | ISL6259 (U7000) | 70 | Main system bus. If absent: check Q7030 gate driver, R7050/R7051 sense resistors |
| PP3V42_G3H | 3.42V | G3H | U7300 | 72 | Powers one-wire circuit (green LED). If absent: no charger LED, check U7300 |
| PP5V_S5 | 5.0V | S5 | TPS51125 (U7200) | 72 | SMC and standby peripherals. If absent: check U7200 pin 16, R7260 feedback |
| PP3V3_S5 | 3.3V | S5 | TPS51125 (U7200) | 72 | SMC core power. If absent: check U7200, C7273 |
| PP5V_S0 | 5.0V | S0 | Q7085/Q7086 | 78 | Active state 5V. If absent: check PM_SLP_S4_L, load switch enable |
| PP3V3_S0 | 3.3V | S0 | Q7087/Q7088 | 78 | Active state 3.3V. If absent: check enable signal from PCH |
| PP1V5_S0 | 1.5V | S0 | U7400 | 73 | DDR3 memory power. If absent: memory won't initialize |
| PPVCC_S0_CPU | 0.75–1.2V | S0 | U7100 (IMVP7) | 74-75 | CPU VCore. If absent: check U7100 VCC pins, ton resistor R7142 |
| PPVCCSA_S0_CPU | 0.9–1.05V | S0 | U7600 | 71 | System Agent supply. If absent: check U7600 enable |
| PPVCCIO_S0_CPU | 1.05V | S0 | U7500 | 76 | CPU I/O supply. If absent: check U7500 |
| PPVOUT_SW_LCDBKLT | 38–55V | S0 | U9701 (lp8550↗/" class="comp-ref" title="LP8550 component reference">LP8550) | 97 | Backlight boost. If absent: check LCD_BKLT_EN, feedback path |
| PP3V3_S0_LDO_AUD | 3.3V | S0 | U5950 | 62 | Audio codec power. If absent: no sound |
Power Tree
DC-IN (MagSafe 18.5V) / BATTERY (10.8V–12.6V)
PPBUS_G3H (12.55V) — Main bus via ISL6259
PP3V42_G3H (3.42V) — One-wire, charger LED
PP5V_S5 (5.0V) — TPS51125 Ch1 — SMC standby
PP3V3_S5 (3.3V) — TPS51125 Ch2 — SMC core
PP5V_S0 (5.0V) — Load switch Q7085/Q7086
PP3V3_S0 (3.3V) — Load switch Q7087/Q7088
PPVCC_S0_CPU (0.75–1.2V) — U7100 IMVP7 buck
PPVCCSA_S0_CPU (0.9–1.05V) — U7600
PPVCCIO_S0_CPU (1.05V) — U7500
PP1V5_S0 (1.5V) — U7400 DDR3 supply
PPVOUT_SW_LCDBKLT (38–55V) — LP8550 boost
Power Flow: MagSafe → ISL6259 creates PPBUS_G3H → TPS51125 creates PP5V_S5/PP3V3_S5 → SMC boots → PM_SLP_S5_L/S4_L/S3_L sequence enables S0 rails → IMVP7 creates CPU VCore → System runs.
Key Components
| Ref | Designation | Function | Rails | Page | Common Failure |
|---|---|---|---|---|---|
| U7000 | ISL6259AHRTZ | Battery charger / PPBUS controller | PP18V5_DCIN → PPBUS_G3H | 70 | No charge, no PPBUS_G3H — liquid damage on SMBus lines |
| U7200 | TPS51125RGER | Dual buck controller 5V/3.3V S5 | PPBUS → PP5V_S5, PP3V3_S5 | 72 | Water damage pin 16 VCC, R7260 feedback corrosion |
| U7100 | ISL95870HRTZ (IMVP7) | CPU VCore buck controller | PPBUS → PPVCC_S0_CPU | 74 | Liquid on VCC pin 20, burns PP5V_S0 trace |
| U7400 | TPS51916 | DDR3L 1.5V regulator | PP5V_S5 → PP1V5_S0 | 73 | Memory not detected — check enable, output caps |
| U7500 | LP2951-33 | 1.05V VCCIO LDO | PP3V3_S5 → PPVCCIO_S0 | 76 | CPU won't boot if missing |
| U7600 | ISL95813HRZ | System Agent VCCSA supply | PPBUS → PPVCCSA_S0 | 71 | No POST if missing |
| U5010 | SMC (LM4FS1EH) | System Management Controller | PP3V3_S5 | 49-50 | Corrupted firmware, liquid damage — no power on |
| U9701 | LP8550TLX | LED backlight driver | PP5V_S0 → PPVOUT_SW_LCDBKLT | 97 | No backlight — check feedback trace, LCD_BKLT_EN |
| U4950 | TI Thunderbolt Controller | Thunderbolt host interface | Multiple rails | 36-38 | No Thunderbolt ports — check U4950 power |
| Q7030 | P-MOSFET | PPBUS input switch | DC-IN → PPBUS | 70 | Shorted — board draws high current on charger |
| F7000 | Fuse 3A | DC-IN protection fuse | PP18V5_DCIN | 69 | Open — no power from charger, battery only |
| R7142 | Ton resistor | Sets IMVP7 switching frequency | CPU VCore circuit | 74 | Missing/corroded — no CPU VCore output |
Boot Sequence
| # | Signal | Value | Condition | If Absent |
|---|---|---|---|---|
| 1 | PP18V5_DCIN | 18.5V | MagSafe connected | Check MagSafe connector continuity, F7000 fuse, DC-In board cable |
| 2 | PPBUS_G3H | 12.55V | ISL6259 switching | Check U7000 ISL6259 ACIN pin, Q7030 gate driver, R7050/R7051 current sense |
| 3 | PP3V42_G3H | 3.42V | PPBUS present | No green LED on charger — check U7300 LDO, one-wire circuit page 50 |
| 4 | SMC_BC_ACOK | 3.3V | Charger detected | ISL6259 not reporting charger — check U7000 pin 25 ACOK, R7015 |
| 5 | PP5V_S5 | 5.0V | SMC requests S5 | Check TPS51125 (U7200) pin 16 VCC, R7260 feedback — common liquid damage point |
| 6 | PP3V3_S5 | 3.3V | U7200 Ch2 enabled | Check U7200 output, measure C7273 — if short, isolate S5 bus consumers |
| 7 | SMC_ONOFF_L | Pulse LOW | Power button pressed | Check keyboard flex connection, power button circuit page 50 |
| 8 | PM_PWRBTN_L | Pulse LOW | SMC passes button | SMC not responding — check PP3V3_S5 to SMC, reprogram SMC if firmware corrupt |
| 9 | PM_SLP_S5_L | 3.3V | PCH exits S5 | PCH not waking — check PCH VCCRTC (page 22), SMC communication |
| 10 | PM_SLP_S4_L | 3.3V | PCH exits S4 | Check PM_SLP_S5_L first — if present, suspect PCH power issue |
| 11 | PM_SLP_S3_L | 3.3V | PCH exits S3 | Memory init failing — check PP1V5_S0, DDR3 connections |
| 12 | PP5V_S0 | 5.0V | PM_SLP_S4_L high | Load switch Q7085/Q7086 not enabled — check gate drive, short on PP5V_S0 |
| 13 | PP3V3_S0 | 3.3V | PM_SLP_S4_L high | Load switch Q7087/Q7088 — check enable, measure PP3V3_S0 to GND (< 50Ω = short) |
| 14 | PPVCC_S0_CPU | 0.75–1.2V | CPU VID request | Check U7100 IMVP7: VCC pin 20 (liquid damage), R7142 ton resistor, high-side FETs |
| 15 | PPVCCSA_S0_CPU | 1.05V | CPU boot | Check U7600 enable, output capacitors |
| 16 | PPVCCIO_S0_CPU | 1.05V | CPU boot | Check U7500 LDO output, input supply |
| 17 | PLT_RST_L | 3.3V | Platform reset deasserted | PCH holding reset — check all CPU rails present, SPI ROM accessible |
| 18 | CPUPWRGD | HIGH | All CPU power good | One or more CPU rails missing — recheck VCCSA, VCCIO, VCore |
| 19 | PPVOUT_SW_LCDBKLT | 38–55V | Display init complete | Check LP8550 (U9701): LCD_BKLT_EN signal, feedback resistor path |
820-3209 Specific: This board auto-powers when charger is connected — fan should spin immediately. If fan doesn't spin but green LED is present, the board is stuck in S5 state. Check PP5V_S5 first (TPS51125 U7200 area is common liquid damage location).
Interactive Diagnostic Engine
Work through stages in order. Complete each stage before unlocking the next. This 820-3209 board auto-powers when charger is connected.
1
Always-On Rails (G3H / Power Source)
Expand ▼
2
Standby Rails (S5 / SMC alive)
🔒 Complete Stage 1 first
3
Active Rails (S0 / CPU awake)
🔒 Complete Stage 2 first
4
Core Voltages (CPU VCore / VCCSA / VCCIO)
🔒 Complete Stage 3 first
5
I/O & Display (Backlight / eDP)
🔒 Complete Stage 4 first
6
Peripheral / USB (Thunderbolt · Audio · Keyboard)
🔒 Complete Stage 5 first
No Power Diagnostic
820-3209 No Power — Complete Diagnostic Flow
The 820-3209 MacBook Air should auto-power when the MagSafe charger is connected. If the fan doesn't spin and you see no signs of life, follow this systematic approach.
Expected Behavior: Connect MagSafe → Green LED appears → Fan spins within 2-3 seconds → Board enters S0 state automatically. No power button press required for initial power-on.
Step 1: Verify Charger and DC-In Path
- Confirm MagSafe charger outputs 18.5V (measure at charger cable tip)
- Inspect MagSafe connector pins on board for corrosion, debris, or bent pins
- Measure PP18V5_DCIN at F7000 fuse input side
- If no voltage at F7000 input: DC-In board or cable fault
- Check F7000 fuse continuity — if open, fuse has blown (often indicates downstream short)
Step 2: Check ISL6259 Charger IC (U7000)
| Pin | Signal | Expected | If Absent |
|---|---|---|---|
| 4 | ACIN | 18.5V | Check F7000 fuse, DC-In path |
| 25 | ACOK | 3.3V | ISL6259 not detecting charger — check ACIN and bias resistors |
| 5,6 | PHASE | Switching | Buck converter not running — check Q7030 gate driver |
| 20 | CSON/CSOP | Sense | Current sense resistors R7050/R7051 open or corroded |
820-3209 TPS51125 (U7200) Repair — PP5V_S5/PP3V3_S5 Missing
The TPS51125 dual buck controller is the most common failure point on 820-3209 after liquid damage. Liquid enters near the keyboard/trackpad and reaches this area.
Critical Inspection Point: U7200 pin 16 (VCC) frequently burns when liquid causes a momentary short. The pad may appear intact but have no continuity to the trace beneath.
TPS51125 Repair Procedure
- Remove U7200 using hot air (HAKKO FR-801 or equivalent, 380°C, air level 10)
- Inspect pin 16 pad location — look for burn marks, missing copper
- Use multimeter continuity mode: probe from pin 16 pad to nearest PP5V_S0 source
- If no continuity: the trace is burned internally — requires jumper wire
- Clean pads thoroughly with flux and solder wick
- If pad is destroyed: scrape back soldermask to expose trace copper, or run jumper wire
- Also check R7260 feedback resistor — often has corrosion underneath
- Install replacement TPS51125 (source from donor board or purchase new)
- Reflow with hot air, then touch up each pin with iron to ensure solder joints
R7260 Feedback Resistor Check
The feedback network (R7260 + C7260) tells U7200 what voltage it's producing. If R7260 has corrosion under it, the chip will oscillate between 5V, 2V, and 0V continuously.
- Remove R7260 and C7260
- Clean pads with isopropyl alcohol and brass brush
- Verify pad-to-trace continuity with multimeter
- Replace with equivalent value resistor/capacitor
820-3209 PPBUS_G3H Short to Ground
If PPBUS_G3H shows very low resistance to ground (< 2Ω), the board has a short circuit that must be isolated before powering on.
Common Cause: PPBUS_G3H shorted by CPU VCore circuit. Failed high-side MOSFET (Q7120/Q7121) can connect PPBUS directly to the VCore output, which is tied to ground through the CPU.
Isolation Procedure
- Measure PPBUS_G3H to GND resistance (unpowered) — normal is > 50Ω
- If < 5Ω: major short present
- Remove L7100 (CPU VCore inductor) — remeasure PPBUS
- If resistance returns to normal: short is in CPU VCore circuit
- Check Q7120/Q7121 high-side MOSFETs for drain-source short
- If MOSFETs are shorted: replace both Q7120 and Q7121
- If MOSFETs OK but short persists with inductor removed: CPU itself may be shorted
No Backlight Diagnostic
820-3209 No Backlight — LP8550 Boost Circuit Diagnosis
The 820-3209 uses the LP8550 (U9701) LED backlight driver. This chip boosts PP5V_S0 to approximately 38-55V to drive the LED backlight string.
Symptom: Fan spins, external display works via Thunderbolt, but internal display is completely dark. Shining flashlight on screen shows faint image = backlight failure, not display failure.
Backlight Diagnostic Steps
- Verify PP5V_S0 is present (required for LP8550 VIN)
- Measure LCD_BKLT_EN at U9701 pin 3 — should be 3.3V when display active
- If LCD_BKLT_EN is LOW: GPU/PCH not requesting backlight (check display detection)
- Measure PPVOUT_SW_LCDBKLT at L9701 output — should be 38-55V
- If boost voltage missing but enable is HIGH: LP8550 or feedback circuit problem
Feedback Trace Issue
The LP8550 monitors its output voltage via a feedback pin. If the feedback trace is broken (common on this board), the chip won't regulate properly.
| Test Point | Expected | If Absent |
|---|---|---|
| U9701 VIN (pin 1) | 5.0V | Check PP5V_S0 (Stage 3) |
| U9701 EN (pin 3) | 3.3V (active) | Check GPU backlight enable signal path |
| U9701 FB (pin 5) | Divided voltage | Feedback trace broken — run jumper wire |
| L9701 output | 38-55V | Inductor or boost circuit fault |
LP8550 Replacement Procedure
- Remove U9701 using hot air (350°C, low airflow to avoid displacing nearby components)
- Clean pads with flux and solder wick
- Inspect feedback trace (pin 5 to voltage divider) — use continuity tester
- If trace broken: identify break point, scrape soldermask, run fine jumper wire
- Install replacement LP8550TLX
- Test backlight before reassembly
Safety Note: PPVOUT_SW_LCDBKLT is approximately 50V. Do not touch this rail or the backlight connector while powered on. This voltage can cause painful shock and damage test equipment.
Liquid Damage Procedure
820-3209 Liquid Damage — Assessment and Repair Strategy
The MacBook Air 820-3209 is highly susceptible to liquid damage due to its thin form factor. Liquid typically enters through the keyboard and accumulates around the CPU power circuitry.
Critical Areas on 820-3209:
- TPS51125 (U7200) area — PP5V_S5/PP3V3_S5 generation
- IMVP7 (U7100) area — CPU VCore generation
- ISL6259 (U7000) area — Charger IC and PPBUS creation
- Audio codec area — near speaker connector
Initial Assessment
- Document liquid entry points before cleaning — photograph "pigeon droppings" stains
- These white/grey residue spots indicate where liquid pooled and evaporated
- Map these locations to board view — identify which circuits are affected
- Look for green/blue corrosion (copper oxidation) under components
Cleaning Procedure
- Remove all shielding — liquid hides under EMI shields
- Isopropyl alcohol (99%) soak — 5-10 minutes in shallow tray
- Ultrasonic clean — 5 minutes at 40kHz in distilled water with surfactant
- Brush corrosion spots — soft brass brush with flux under microscope
- Rinse with 99% IPA — remove flux residue
- Dry thoroughly — hot air station at low temp, or oven at 50°C for 30 minutes
Post-Cleaning Inspection
- Examine documented damage areas under microscope
- Check for lifted pads, corroded traces, burned components
- Test continuity on all power rails before powering on
- Measure critical resistances to ground (see Short Circuit section)
Pro Tip: If the board was cleaned before you received it (no visible corrosion), check the machine's case for liquid residue patterns. These patterns reveal where liquid was on the board, even after cleaning.
Short Circuit Methods
820-3209 Short to Ground — Localization Methods
Method A: DC Injection (Preferred)
Inject controlled DC voltage into the shorted rail and use thermal camera or finger to locate heat source.
| Rail | Inject Voltage | Current Limit | Max Duration | Normal Resistance |
|---|---|---|---|---|
| PPBUS_G3H | 1.0V | 3.0A | 30 sec | > 50Ω |
| PP5V_S5 | 1.0V | 2.0A | 30 sec | > 100Ω |
| PP3V3_S5 | 1.0V | 2.0A | 30 sec | > 100Ω |
| PP5V_S0 | 1.0V | 2.0A | 30 sec | > 50Ω |
| PP3V3_S0 | 1.0V | 2.0A | 30 sec | > 50Ω |
| PPVCC_S0_CPU | 0.5V | 5.0A | 20 sec | > 5Ω |
| PP1V5_S0 | 0.5V | 2.0A | 20 sec | > 20Ω |
Important: Always start at low voltage (0.5-1.0V) and increase slowly while monitoring current. If current limit is hit immediately, you have a hard short — use thermal detection.
DC Injection Procedure
- Set bench PSU to specified voltage and current limit
- Connect positive lead to shorted rail, negative to ground
- Enable output — watch current draw
- If current limiting: scan board with thermal camera or wet finger
- The shorted component will heat up — this is your target
- Remove suspect component and remeasure resistance
- If short clears: you found it. If short persists: continue searching
Method B: Thermal Camera
Use FLIR ONE or similar thermal camera while injecting DC. Short circuits dissipate power as heat, making them visible.
- Best sensitivity: inject current for 10-15 seconds before imaging
- Look for hotspots that don't correspond to normal power components
- Capacitors on shorted rail may warm slightly — the actual short gets HOT
Method C: Divide and Conquer
When thermal methods are inconclusive, systematically isolate sections of the shorted bus.
- Identify all major consumers on the rail (use schematic)
- Remove ferrite beads or inductors that feed sub-sections
- Remeasure resistance after each removal
- When resistance returns to normal: short is in the section you just isolated
- Continue dividing that section until you find the specific component
Common Short Circuit Culprits on 820-3209
| Rail | Common Culprit | Location |
|---|---|---|
| PPBUS_G3H | Q7120/Q7121 (VCore high-side FETs) | Near U7100 |
| PP5V_S5 | U7200 TPS51125 internal short | Power supply area |
| PP3V3_S0 | U4950 Thunderbolt controller | Near Thunderbolt port |
| PPVCC_S0_CPU | CPU die short (rare but possible) | Under CPU |
| PP1V5_S0 | DDR3 RAM chip short | Memory area |
Measurement Points
| Rail / Signal | Test Point | Expected Value | Schematic Page |
|---|---|---|---|
| PP18V5_DCIN | F7000 input pad | 18.5V DC | 69 |
| PPBUS_G3H | F7000 output pad / C7020 | 12.55-12.8V | 70 |
| PP3V42_G3H | L7300 inductor | 3.42V | 72 |
| PP5V_S5 | C7273 capacitor top | 5.0V | 72 |
| PP3V3_S5 | C7283 capacitor top | 3.3V | 72 |
| PP5V_S0 | Q7085 drain | 5.0V (S0 active) | 78 |
| PP3V3_S0 | Q7087 drain | 3.3V (S0 active) | 78 |
| PP1V5_S0 | U7400 output inductor | 1.5V (S0 active) | 73 |
| PPVCC_S0_CPU | L7100 inductor output | 0.75-1.2V (load dependent) | 75 |
| PPVCCSA_S0_CPU | U7600 output | 0.9-1.05V | 71 |
| PPVCCIO_S0_CPU | U7500 output | 1.05V | 76 |
| PPVOUT_SW_LCDBKLT | L9701 output (CAUTION: 50V) | 38-55V | 97 |
| SMC_BC_ACOK | U7000 pin 25 | 3.3V when charger connected | 70 |
| PM_SLP_S5_L | PCH pin (via test point) | 3.3V when exiting S5 | 79 |
| PM_SLP_S4_L | PCH pin | 3.3V when exiting S4 | 79 |
| PM_SLP_S3_L | PCH pin | 3.3V when exiting S3 | 79 |
| LCD_BKLT_EN | U9701 pin 3 | 3.3V when backlight requested | 97 |
| R7142 (Ton resistor) | Between IMVP7 and GND | Continuity / specified resistance | 74 |
Recommended Tools
Multimeter
Fluke 87V or equivalent — DC voltage, resistance, continuity with audible beep
Microscope
Stereo microscope 7x-45x zoom — trinocular preferred for video recording
Hot Air Station
HAKKO FR-801 or Quick 861DW — temperature controlled, multiple nozzles
Soldering Iron
HAKKO FX-951 or JBC CD-2BE — fine tip (T15-D08/C245-030) for SMD work
DC Power Supply
0-30V, 0-5A adjustable bench PSU — for DC injection fault finding
Thermal Camera
FLIR ONE Pro or Seek Thermal — for locating short circuits
Ultrasonic Cleaner
40kHz, heated — for liquid damage board cleaning
Board View Software
OpenBoardView — free, open source, reads .brd files
Flux
Amtech NC-559-V2-TF or equivalent no-clean flux
Solder Wire
Leaded 63/37, 0.3mm diameter for fine SMD work
Solder Wick
2.0mm and 1.5mm width — for pad cleaning
Jumper Wire
38-40 AWG enameled copper — from old MacBook battery connectors
Frequently Asked Questions
What is the most common failure on the 820-3209 MacBook Air logic board?
The most common failure is liquid damage to the TPS51125 (U7200) power supply area, specifically pin 16 VCC burning out. This causes PP5V_S5 and PP3V3_S5 to be missing, resulting in a board that shows a green charger LED but won't power on. The repair involves running a jumper wire to restore the damaged trace and often replacing U7200 itself.
Why does my 820-3209 show a green LED but the fan doesn't spin?
A green LED indicates the one-wire circuit (powered by PP3V42_G3H) is working, but the S5 standby rails may be missing. The 820-3209 should auto-power when the charger is connected. Check PP5V_S5 at C7273 — if zero volts, the TPS51125 (U7200) is likely damaged from liquid exposure. This is the #1 cause of "green light, no power" on this board.
How difficult is the TPS51125 repair on the 820-3209?
This is a Level 3 repair requiring hot air rework skills and possibly jumper wire soldering. The TPS51125 is a QFN package that requires proper flux application, controlled hot air temperature (380°C), and careful pad inspection afterward. If pin 16 trace is burned, you'll need to run a fine jumper wire from the chip to a PP5V_S0 source — this requires good microscope work and steady hands.
What tools do I need to repair a 820-3209 liquid damage board?
Essential tools include: a good stereo microscope (7x-45x), hot air rework station (HAKKO FR-801 or equivalent), precision soldering iron with fine tip, multimeter with continuity beep, ultrasonic cleaner for board cleaning, and bench power supply for DC injection testing. For thermal fault finding, a FLIR ONE thermal camera is extremely helpful. Budget approximately $1500-2500 for a complete setup.
Can I recover data from a liquid-damaged 820-3209 if it won't power on?
Yes, in most cases. The SSD on MacBook Air 2012 models is a removable blade-style drive. You can remove the SSD and read it using a compatible USB adapter (OWC Envoy or similar) on another Mac. If the SSD itself was damaged by liquid (uncommon since it's usually away from liquid entry points), data recovery becomes more complex and may require professional services.
What causes PPBUS_G3H to be shorted to ground on the 820-3209?
The most common cause is a failed high-side MOSFET (Q7120 or Q7121) in the CPU VCore circuit. When these MOSFETs fail shorted, they connect PPBUS_G3H directly to the VCore output, which is effectively a short to ground through the CPU. To diagnose, remove L7100 (VCore inductor) and remeasure PPBUS resistance — if it returns to normal, the VCore circuit is the culprit.
How much does professional repair of a 820-3209 liquid damage board typically cost?
Professional board-level repair for liquid damage on 820-3209 typically ranges from $150-350 depending on the extent of damage and components needed. Simple TPS51125 replacement is on the lower end; repairs requiring multiple component replacements, trace repairs, and extensive jumper wiring are higher. This is significantly less than logic board replacement ($400-600) and preserves the original board with its serial number and data.