Need a little advice to fix my CR20 Pro

Hi, I became a recent owner of a non-working CR20 Pro. The previous owner (allegedly) was using it just fine with Marlin V1.1.6. He upgraded it and it now has a TCM connection error. He gave up and sold it to me. This is my first venture into 3D printing. I have a steep learning curve here.
My unit is a CR20 Pro with a BigTreeTech SKR E3 DIP V1.1 board, 3D auto leveller and a standard LCD. The bed is a glass/ceramic plate , I think.
First, does anybody have a proper firmware that they would share? (Save a lot of work at this end.)
Even if the firmware didn’t have the autoleveller, I could test it for function, I think.
He gave me some files he was working with. One is his firmware that gives Marlin V2.0.1, but with the mentioned error. I have been able to reload it when I try something that doesn’t work.
I can make the printer do lots of functions. Home at X,Y and Z. Auto-level, ( but not Zeroed at the extruder tip, I expect to do that when the error is corrected.)
I also found that the Extruder driver (TMC2208) had its jumper set to DIR , not UART as the others did. I made them all the same, hoping the new firmware would maybe help.
( the changed jumpers made no obvious difference)
I can heat the tip, change filament, heat the bed.
I can use Pronterface and make it home as well, make it move hither and yon…
I am trying to learn what some of the G & M codes are and can get different readings and so on.
However, as I try to learn how to modify and update Marlin to fit this printer I constantly get errors in the code.
I installed a version of Marlin ( via SD card) for an Ender 3 and have no screen output, but I can make it work under Pronterface. It has different setups so it will stroke the bed out if I let it.
I believe the board should be ok if I could only get the firmware compiled.
I have been trying to see if I can compile even an example of Marlin for a similar board, but still have errors.
Now, who can list for me just the software I need and the proper extensions. I find that rather confusing. Do I need Autobuild?, Intellisense? and so on.
I loaded Visual Studio and a bunch of recommended extensions, but Intellisense still said it wasn’t working.
So I removed it all, figuring to start over from scratch.
I am a senior citizen, (OMG) and spent my working years as a machinery mechanic.
Thanks in advance

I am often not the best for advice in mod land.

You have bough a Lada that someone tried to make a BMW. (ok hongqi not a Lada)

My advice is strip it back to original, Replace the firmware with the factory and get the unit working. Make sure it is running well and you are comfortable using it. There is no guarantee the parts or work is good and causing fault.

Then once you have a handle on how it behaves and what to expect you will be better placed to upgrade what you need or decide to buy something else instead of putting the time in.

Thanks for the advice.
My first issue is trying to get BTT SKR E3 DIP to compile at all. It always comes up with errorsfor me.
I did get a Marlin with megaatmega2560 to compile, but that doesn’t help me.
I cannot strip the unit back, because the only thing to remove would be 3DTouch.
It only has the board that is in it.

Should I get a different board?
Which one?

You could try Marlin Firmware Service. You pay an annual subscription fee that lets you use the builder and also gives you access to their daily builds.

Marlin Firmware Service (

I second this. I have used their custom firmware builder with good success on my Ender 3s. It looks like they have the CR20 Pro under the builder list of options, but not on the pre-compiled list of firmware.