Extruder Skipping, looking for suggestions

Bambu Lab A1 Series Troubleshooting
1

Hi, folks!
I’m having issues with my A1 mini skipping and not extruding correctly.

About me: I’m pretty mechanically inclined, the A1 mini is my third printer. I have also had a Creality S1 Pro ( not good ) and currently have a Creality K1C ( good ) that I use mostly for personal projects in filaments the A1 can’t really print, like ASA and Nylon.
The A1 mini has been a workhorse for me for about a year, printing a product that I sell, though for the last month I’ve had to fall back on doing those prints on my K1C. I print these products exclusively in Crealty PETG, which I’ve had really good luck with.

Recently, my A1mini started skipping intermittently, like it had a clogged nozzle. This seemed odd, since I had printed for over 1.5k hours on the original hot end and only changed it because I was concerned that quality was slipping, which after the change I’m not sure it was. I’m using Bambu hot ends with hardened steel tips and the hot end temp ( 255C) looked fine. The heat break fan seemed to be working fine and I cleaned any dust off of it. I had some spare hot ends so I changed it again and the problem didn’t get better.

I then ordered a new set of Bambu extruder gears and while I was in there I made sure there was no debris in extruder. No change.
I changed the hot end again. No change. I tried a few different rolls of the same filament ( I go through 4-5 a month ) with no change and they worked fine on the K1C.
I ordered some BIQU gears. No change. I tried a third hot end. No change. Full printer reset. No change.

At this point, I noticed that when the gears skip, you can see the hot end move. It shifts down a few mm, then as the “click” happens, you can see it snap back upward, showing that the resistance to the filament is in the hot end/nozzle, as if it wasn’t really getting as hot as the measurements said.

It was about this time I noticed something I thought was unrelated, but now am not so sure. When the printer was idle, the bed temp showed low. My room temp is about 22C, yet when the printer was idle the bed and hot end temps showed very different temps. My bed showed just 5C, though the nozzle seemed to be more or less correct at 21C.
I also noticed that the bed was unable to reach the 70C that it was set to for printing PETG, seeming to limit out at about 66C. So I set the mini into maintenance mode and set the bed to 70C. When the temp peaked ( 66C on the display ) I measured it with an IR thermometer and it was actually a bit over 80C. I opened a case with Bambu and they’re sending a new build plate with thermistor.

However, that got me to thinking, maybe the hot end temp isn’t being measured correctly? I set the hot end to be 255C and let it get good and warm. Then while it was still at that set temp, I quickly popped the hot end off and measured with the IR thermometer behind the hot end, where the heater transfers the heat to the hot end.
According to my thermometer, it was just 170C at the heater, despite the printer thinking it was 255C.

If my hot end is only getting to 170C, PETG would of course clog and the extruder would skip.

Any suggestions on how to confirm this or resolve it? I understand that the extruder assembly is driven by a USB C cable and that it has a daughterboard. If the hot end isn’t at the correct temperature, is there a way to confirm the operation of that board?

This printer makes me a few thousand dollars a month, I either need to get it back functional or I guess I need to buy a new one and keep this one for parts.

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Do you have a picture?
Because I think I have the same problem.
Maybe we can solve it together

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Sure. What would you like a picture of? It looks normal, AFAIK.

4

Maybe from the first layer, because it very wavy at my prints

5

As long as it’s not skipping, my first layers are great. Here’s a failed print. There’s some elephant foot, but I think that’s from the bed being a lot hotter than the setpoint.

In this print, my failures are at roughly layer 75, 100 and 120. Since this print, underextrusion got worse and more frequent.

PXL_20250226_171218429
PXL_20250226_1712184291920×1080 198 KB

6

If your seeing the hotend actually move…it’s probably these screws.
If not, the nozzle holder (heater).

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My experience with my previous printers, one of which needed mostly manual level and Z offset, is that if you’ve got wavy first layers, the nozzle is too close to the build plate.
I’m not sure how to solve that with a printer that’s supposed to auto level, like the A1.
Most of the time, I haven’t had any issues with the leveling unless I’m printing something that really needs perfect level and is using the entire bed, like some of the 3d printed “chain mail” I’ve printed. In that case, one of my corners doesn’t have a good z offset and I get poor first layer quality and adhesion in that part of the plate.
For those things, I just print them on my Creality, it seems to do bed leveling a bit better than my A1, but that’s a really small amount of what I print so it’s not a big deal.

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WAIT. There are screws BEHIND the heater?
Thanks so much for that. I’ll check those as soon as the heater is cool again.

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OK, so I pulled off the heater.
The screws were kind of loose(ish), so I’m not positive that was my issue, but part of the heater looked broken and the act of turning the heater around made the heater wires come loose.
It looks like maybe they overheated and desoldered themselves? Or perhaps flexed and fatigued?
Regardless, they’re hooped and I need to replace the heater. I’ll update my case with Bambu and probably just order a new part since this printer makes me $$$ and if it happens again I’ll want a spare.

Thank you very much for the suggestion. I’ll update in a few days when the new part gets here.

PXL_20250306_213135593 (1)
PXL_20250306_213135593 (1)1568×1816 327 KB

1 Like
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Now for the fun part…

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Thanks. I’m pretty good with the actual taking things apart and putting them back together, so I’ll follow that guide.
I’m pretty stoked that I think I have the issue identified.

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Don’t know if the A1 hotend assemblies are the same as my P1S but if they are you might want to refresh the thermal paste also if you didn’t already cover that.

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They are not the same and AFAIK ( read the wiki ) there’s no thermal paste needed for A1s.
Thanks for the suggestion, though.
My new hotbed is here, heater assembly should be here in a day or two, then I’ll replace both of them.

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Update:
Bambu send me a new hotbed as a one-time courtesy to fix the thermistor issue and I bought another hot end for the extruder. It took an hour or so to swap out both items and while that fixed my bed heating/temp issues, the hot end did not fix my underextrusion issues.

I got one good print off the printer and on my second try I had the same quality issues part way through the print that I had before replacing the broken hot end.
This time I KNOW that all the screws are tight since I just installed the hot end.

I’m at my wits end with this A1mini and am not sure what to try next. I’ve shifted all the printing for my business to my Creality, so it hasn’t stopped my income stream, but I’d really like to not have to buy a whole new printer just because I can’t get this A1 to print, even with a bunch of new parts.

Again, I’m open to suggestions.

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Have you tried a new nozzle…??

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Three of them, all from Bambu.

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Re-reading the 1st post, you never said if your using an AMS Lite or not.
I did see that you said you’ve printed 1.5k hours on the nozzle, which you did replace along with the gears…but have you replaced the bowden tube…??
What about the filament hub…??

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No AMS, I print almost exclusively in one filament ( Black Creality PETG ) from the filament holder on the printer or from my filament dryer. There is very little drag on the filament through the bowden tube, though it’s original and looks/works fine. With the nozzle not in place the extruder easily moves the filament with no problems and I’ve repeatedly checked the filament path for obstructions.

I had ~1500 hours on the first nozzle, most of that printing the same PETG I am currently printing. That first nozzle never clogged, but after that long ( and after my early experiences with changing Creality nozzles on my Ender 3 series every few hundred hours ) I changed it anyway.
I have maybe another 500 hours on the printer since then and when this issue started is when I replaced the extruder gears, both with OEM and with BIQU all-metal gears. I’m back with the OEM gears with only a few hours of testing on them.

19

I’m having the same issue, not with PETG but Bambu PLA. I have a ticket opened, but sending messages is like communicating with the rovers on mars, it take 3-4 days for a response.

Extruder skips while purging and after the first layer. Bambu has sent a new hot end and a new Tool head control board, and no luck.

Mostly replying in case you get your’s working and I can try new ideas…