H2D AP board diagnosis — visual guide

Compiled from Bambu Lab's wiki (AP board replacement, MC-AP cable, toolhead cable, purge chute, rear panel, indicator LED reference and the electronic connector guide). Images and videos are Bambu's own; filenames and captions are mine.

Rule that applies to every picture below: power off, mains cable out, safety key out, before any connector is touched. Bambu's guides are unanimous on this - the isolation tests require powering on with the machine open, but connect/disconnect always happens dead.

1. LEDs: what normal looks like

The three videos below are Bambu's own reference clips. Watch the MC one all the way through - the bottom-left LED stays SOLID for the first few seconds after power-on and only then starts its slow blink. That is the 'cut short' blink you filmed.

MC board: normal = top-left solid, bottom-left slow blink, right fast blink. Includes the boot-initialization phase.
AP board with the cover off: left LED must fast-blink, right LED steady.
The same AP LEDs seen through the cover's vent slots - no disassembly.
AP LEDs, alternative viewing angle.
AP LEDs with the cover fully clear.

2. The AP board connector map - the single most useful picture

Every plug on the AP board, numbered. Match this photo to the board in front of you before you pull anything. For the isolation test you keep ONLY 5 (MC-AP communication, the multi-colour wire bundle) and 6 (MC-AP power, the red/black pair).

AP board, numbered 1-8. 1 screen FPC / 2-3 LED light connectors (red = left, blue = right) / 4 USB port board / 5 MC-AP communication / 6 MC-AP power / 7 live-view camera / 8 USB-C to toolhead.

3. Getting the AP cover off

One BT2.6x8 screw, H2.0 key. Hinge the cover open from the edge nearest the front door. The cover does not need to come off completely - just expose the board.

4. Close-up of the AP board with cables in place

Real machine, cover off. Note how tight the harness is around the MC-AP cables and the USB-C; this is the area to inspect for a pinched or chafed cable.

AP board region with cabling in place. The blue 'AP'-marked ribbon on the right is the screen cable.

5. MC board access (only needed if the MC LEDs are ever abnormal)

Screw counts for the rear panel: 11 x ST3x6 machine screws + 12 x BT3x8 self-tapping, plus 2 x ST3x12 on the spool bracket. Then one BT3x8 frees the purge chute.

Purge chute: the single screw.
Purge chute: pull downward to expose the MC board.
MC board with its silkscreened connector numbers 1-32 (motor phases B/Z/A along the bottom edge). Part Two refers to connectors by these numbers - read the tiny printed number beside each plug before pulling it.
The MC-AP Cable Pack is a 2-in-1 part: power (red/black) + communication (black). Replaced as a pair.
The MC-AP cables where they land on the MC board side.

6. Connector types - how each one opens

Bambu's own connector catalogue, one image per family. The three you must not get wrong on the AP board: the FLIP-TYPE FPC (screen cable - flip the latch, never pull the ribbon), the IPEX antenna (lift straight up), and the USB port board connector (peel the soft adhesive first).

Flip-type FPC - screen cable style. Flip the latch open, then slide the ribbon out.
Drawer-type FPC - pull the drawer out, insert ribbon, push closed.
IPEX Gen 1 Wi-Fi antenna - lift vertically, do not lever sideways.
MX 1.25 mm with lock.
GH 1.25 mm with lock.
PHD 2.0 mm with lock.
HY 2.0 mm with lock.
MX 3.0 mm with lock.
XT30 / XT60 power connector.
BTB 0.8 mm board-to-board.
MX 1.2 mm 78171/78172.
Non-self-locking receptacle terminal.
Self-locking receptacle terminal.
LVDS high-definition screen cable.

7. Order of operations for the next test

  1. Power off, mains out, safety key out.
  2. Open the AP cover — 1 × BT2.6x8, H2.0.
  3. Unplug everything except 5 and 6 (section 2 photo).
  4. Power on. Read the AP LEDs (section 1 videos).
  5. Power off before touching anything again.
  6. AP blinks now → refit connectors one at a time, USB-C last; the one that breaks it is the bad part.
  7. AP still dark-blink → unplug 5 and 6, power on, watch the MC LED. MC recovers = AP board. MC stays abnormal = MC-AP cable pack.
Reassembly order on the AP board
Left side: 1 → 2 (blue → red) → 3 → 4
Right side: 7 → 8 → 6 → 5

USB-C connector: the side marked A faces outward.

Before closing the cover, check no cable is obstructing the PTFE tubes - Bambu calls this out explicitly.