Request to check warped bed diagnosis and next steps  

Request to check warped bed diagnosis and next steps

TL;DR Looking for some help to confirm the diagnosis of a warped bed (or suggest alternatives) and advice on next steps

I have had a Prusa MK3S with MMU2S for several years. The MK3S has been very reliable, the MMU2S less so. Last weekend I upgraded to the Mk3S+ and MMU3, and also replaced the hotend at the same time. Perhaps somewhat foolishly I did the Mk3S+ y axis upgrade as well as the extruder upgrade, even though I didn't strictly need to. I now have problems with my first layer with apparently large differences in z offset across the bed. See image for latest failed print - you can see that the layers are too squished at the corners and not squished enough in the middle. I think that poor adhesion due to insufficient squishing caused some of the filament to come loose. I also considered that maybe this was caused by a blob escaping from the hotend, but when I inspected the hotend it was very clean so I don't think this

was the cause

Print failure

This was on a satin sheet, PLA, sliced in PrusaSlicer. I redid xyz calibration (and thermal model, PID) after doing the upgrade with "slightly skewed" result. I have 7x7 mesh bed leveling switched on with 5 points per location and the default magnet setting. I have printed this same print successfully before doing the upgrade. I have tried the print multiple times including with a smooth sheet.

My suspicion is that I have warped the bed somehow during the upgrade. This seems to be confirmed by G80/G81 results which show a high spot in the front right and lower spots at all the other corners. The bed level calibration test print also seems to imply warping, but it is difficult for me to compare this to the G81 results because the bed level calibration is applying mesh bed leveling. I don't see any obvious warping with a visual inspection. 

>>> G81
SENDING:G81
Num X,Y: 7,7
Z search height: 5.00
Measured points:
0.12800  0.12100  0.13050  0.16700  0.22250  0.07100  0.01250
0.15900  0.17500  0.18850  0.28100  0.29650  0.19350  0.09250
0.16100  0.20850  0.23550  0.26188  0.29150  0.24600  0.16050
0.13450  0.16750  0.14950  0.23950  0.26500  0.24850  0.18350
0.15600  0.17800  0.17950  0.23325  0.28050  0.30800  0.24500
0.14050  0.18300  0.21050  0.23350  0.36150  0.39300  0.29450
0.16250  0.19550  0.24450  0.26500  0.35800  0.37750  0.36600

Things I have tried:

• Loosening heat bed screws and retightening both in Prusa assembly instructions order and in the "center last" order
• Adding a -50µm adjustment in bed calibration to right and front sides
• Swearing

My next step is going to be to dismantle the y axis and reasssemble with great care. I will see if I can use the torque wrench I bought for extruder assembly to put uniform tension on all the bolts.

My questions:

1. Am I right that this is bed warping or could something else be causing the issue?

2. Any other suggestions on next steps?

Thanks!