u/Positive_Ad_313

Hi All
I have issue to fine tuned my bed leveling on my MK3S+ that I bought as a second hand.
Since the beginning, It's very difficult on my printer to keep a decent and consistant bed leveling and I will add that, as a consequence, my printing outputs are really inconsistant.
I used Prusa help website, Forums, Youtube, and roughly no real improvements.
Anyway...I got fed up several times, and sometimes I was wondering how a MK3S+ could fly from the second floor...
I have a look earlier today on the bottom side of the heatbed, and I noticed that the screws holding the linear bearing clips were tightened by M3nN nylock nuts, but I realized that up to 4 of their screw were exceeded the nut, enough to touch the heatbed too ...which is certainly not the best mount, and possibly be one of the reason explaining my bed leveling adjustment issue....

I did search and reading the Prusa Help website and read back the MK3S+ original kit assembly, and found that 2 mounts exist : Old Frame vs New Frame...and on the E-shop, the spare Y-carriage is now the same for MK3 to MK4S.
my MK3S+ being an old frame version, the screws exceeded the nuts are probably not the ones given by Prusa (M3x12mm) and probably slightly longer (M3x14mm may be).

As on the new frame , there are no nuts, I assume that, on this last version of the Y-carriage,the 6 holes maintaining the bearing clip for the LMMU8 are threaded.

Can someone please confirm that the 6 holes on the new Y-carriage are threaded or not as it is not written on the e-shop ?

Also, according to experience, I wonder if someone already threaded the old version ? or the best option is to buy a new Y-carriage ?
I prefer to ask before to disassemble it !

thanks

As a first step beforento use my MMU3,I modified the extruder , adding the chimney on top, following the instructions in the link attached. https://help.prusa3d.com/guide/9b-mk3s-mk3-5-extruder-mod-kit_420370#422234 for my Prusa MK3S+ (firmware 3.14.1-8237), and changed also the adapter-printer-mmu without the steel ball.

My issue is that the filament detection failed.

I first check the wires orientation on the sensor, as well as on the motherboard connection: both well connected.

Then I unscrewed the sensor and removed the top of the chimney and the sensor itself to clean and remove any dust using a small blower : detection failed too.

Sensor Voltage is 0.4V or newer without filament, given in the support menu, which means that the connection is good.

But sensor value obviously stay to 0 for the filament sensor. (the SPinda sensor works fine).

I finally try to tighten and/or loosen the screw of the extruder idler, the screw of the sensor cover, the screw on the chimney base to maintain the chimney itself, and the screw which maintain the chimney base to the extruder.

As I had a second filament sensor, I also swap it.: Failed...

I don't know what to do more to be honest.

if someone has an idea , and/or experience a issue like mine, it will be fantastic.