Well it looks like another waste of time on a down-the-rabbit-hole theory, concerning any motherboard creation date similarities having any real bearing on the MDD J20 RAM slot problem. Mardeec’s mobo info on top and mine directly underneath it. Both with the J20 slot problem.



So it seems entirely more likely, as we had previously suspected (me, peeperpc and GaryN) that the J20 slot suffers (over time und zee heat) from its close proximity to the GPU. Whether that GPU is some high performance (and thus, likely operationally hotter GPU) or some perhaps lesser capable (overall cooler running) GPU.

Again, please refer to Gary’s extremely well-explained post on the subject here:
https://macos9lives.com/smforum/index.php?topic=7637.msg59356#msg59356

Don’t we always have f-f-f-fun?

Ahh, to only “suffer the slings and arrows of outrageous fortune”!

Amen fratello!

  

When the computers were being actively used and supported, the null-modem MiniDIN-8 was the only type of serial cable a user was likely to find in a computer store. Far from being some kind of exotic thing they had to solder themselves.

definetly a blue ice. no idea about their exact models and software compatibility.

They look almost identical but with big granddaughterboard

Possibly "related"?



See / read: https://www.provideocoalition.com/after-effects-performance-part-4-bottlenecks-and-busses/

I ordered G4 Sawtooth and i can't identify this expansion card that i will get with it

Update... tick tock tick tock 
This story is going to make me suffer  until the very end! :-)

The technician who was supposed to assemble the cable  is a nice  old  technician who has worked for 50 years on  radio and TV repairs and he said to me, "Oh Mario, I'm sorry, but  my hands and my eyesight  no longer allow me to do this kind of work. The  8 pins  to be soldered are too small, you need a steady hand.  Let's wait for the young guy who is just learning  the job to come back,  he's  away for a few days."
And I wait...

this makes sense, either you or your elves must have been doing that, as the hardware or OS9 will never do something like this.

however, it is generally not a bad idea to have a second system folder on the second disk, eventually a backup, but even better a juvenile, fresh install, so that you can easily boot from the second drive when something goes wrong with #1. (note that in order to boot OS9 from a drive, the boot partition may not exceed 192 gb.)

when you make backups from your system folder and do not want it to be bootable, use disc copy or toast to make image files, as this is much faster than using stuffit.

Of "some" possible interest here, in this matter...