Adhesion problems after upgrading  

Adhesion problems after upgrading

I upgraded an MK3S+ to MK3.5 a few months ago. Previously, the MK3S+ was working "perfectly" in that virtually everything I tried to print succeeded in one attempt with great print quality. I am printing mostly in PETG and PLA and on the smooth steel sheet. But of course I had to fix was wasn't broken and decided to upgrade to the MK3.5 for the speed boost.

Now, the print quality is fine when it works, but many prints fail due to lack of adhesion unless I add significant brims. Recently I attempted to print in TPU for the first time and read the Prusa article about needing to use the textured steel sheet since TPU adheres so strongly to the bed. This part (which granted is not as large and some others I print) easily fell about 15 minutes in. I switched back to the steel sheet and was able to successfully print it but even then it easily popped off the smooth steel sheet.

I have re-run the first layer calibration many times and also used other first-layer test print parts. Every time I end up with the same z-offset results and my first layer looks totally fine in terms of the distribution of material on the build plate. The only potentially weird thing is my Z offset is almost exactly 1.00mm different than what it used to be: -1.280 versus before upgrading is was about -0.280. Not sure why that would be exactly.

This is the same steel sheet I was using from the MK3S and I clean it the exact same way with 91% rubbing alcohol. I tried flipping the steel sheet over to the side I never used and cleaning it with the same results. And as I mentioned I switched sheets entirely to the textured which I literally opened from the packaging to use with TPU and that print failed within 15 minutes after losing adhesion.

I have measured the bed temperature and the heater is working and accurate.

I print from a dry box, and I have even purchased new rolls of e.g. PLA thinking perhaps they are just too old but the results are the same.

I have also just slowed prints down dramatically, especially on the first layers, but it actually makes it worse since the longer the print goes on, the more likely it will separate from the build plate.

I understand adhesion is almost always Z offset or build plate problems, but I am out of ideas of what else to check. Any ideas would be welcome.