H2S - AMS not detected after filament buffer replacement

Bambu Lab H2 Series Troubleshooting
1

I’m hoping someone has run into this before because I’m running out of ideas.

Original issue

My H2S’s filament buffer failed. The PTFE coupler would no longer couple the PTFE tube, so the tube would immediately back out.

I replaced the entire filament buffer with a replacement from Bambu.

New issue

After replacing the filament buffer, neither of my AMS 2 Pro units are recognized by the printer. The AMS system was functioning normally immediately before replacing the filament buffer.

Symptoms:

  • Both AMS units have all 8 LEDs flashing red.

  • The printer reports no AMS connected.

  • Bambu Studio also shows no AMS connected.

  • The filament buffer PCB has a flashing green LED.

Troubleshooting performed

At this point I’ve ruled out quite a bit.

Ive tried:

  • Installing the new OEM filament buffer.

  • Reinstalling the original filament buffer PCB.

  • Replacing the entire harness from the filament buffer to the MC board with the new harness that came with the replacement buffer.

  • Reseating all connectors multiple times.

  • Power cycling the printer completely after each change.

  • Verifying the harness and connectors appear undamaged.

The behavior is identical regardless of which buffer PCB or harness is installed.

Current status

The printer itself appears to function normally, but neither AMS is detected.

Since both AMS units disappeared simultaneously, I don’t think the AMS units themselves are the problem.

At this point I’m wondering if:

  • there’s something I’m overlooking,

  • there’s an additional connector or diagnostic I should be checking,

  • or if the issue points toward the MC board or another communication component.

Has anyone experienced this after replacing the filament buffer or have any suggestions for additional troubleshooting? Or should I use this as an opportunity convince my wife its knackered and I NEED to upgrade to an H2C?? (slightly joking…but only slightly)

2

Have you gone through this troubleshooting procedure?

In my opinion, it’s most likely a connection issue between the buffer and the printer’s MC board. On the X1/P1 models, when the buffer was external, the connection chain went MC Board →Buffer→AMS, so if there was a disruption at or before the buffer, the AMS would not be able to communicate. Although the H2 series is physically different with the buffer being internal, the control theory is the same, and given the interoperability among all AMS products, I expect the same underlying architecture is present - so if the buffer isn’t connected properly, the AMS units won’t be able to communicate.

3

While not specifically measuring resistance of the ams cables, I did the ole switcheroo between cables and ams and printer (ams 1 with cable 1 to ams 2 to cable 2 to printer, ams 1 cable 2 to ams 2 to cable 1 to printer and so on) with all the same results.

The changing of the harness between the buffer and MC board was what I really thought would solve the issue but no.

It’s just weird that everything worked, I changed one component and now it doesn’t work and still doesn’t work if I go back to the original components.

4

Is there a chance you damaged something on the MC board, or perhaps you haven’t connected the harness to the MC board properly?