Fairchild Channel F Model 2 - RAM type?

[Middleway]

I have a NTSC Fairchild Channel F with a graphics problem (see screenshot).  It's a Model 1 with the hardwired controllers, internal speaker, etc.  However the inside appears to be the VLSI version that I understand is what you would find in a Model 2.  Through swapping around the RAM chips I believe I've narrowed down the issue to 1 bad RAM chip.  I have some MK4027N-3 replacement RAM, however replacing the bad chip resulted in a black screen and the new chip getting very hot in a matter of seconds. 

 

As I started digging into it further I found a schematic of the SABA VideoPlay 2 which matches my motherboard (other than it is PAL vs NTSC).  The RAM is labeled "330470" which also matches the label on mine.  But it seems to be different RAM than the MK4027N-3.  For example, the 330470 has -5v/+12v/+12v input voltage lines, while the MK4027N has -5v/+5v/+12v.  The A0/A1/A2 address lines are different between them as well.  When I measure the voltage on my RAM it matches up to the +5v/+12v/+12v on the SABA schematic.  There is a reference on VESwiki to using MK4015N as replacement RAM for the VLSI version, but it has the same voltage inputs as the MK4027N.

 

So it's left me scratching my head a little.  It seems like there's a fundamental difference in the 330470 RAM type on the Model 2 board, but my Google fu has come up empty on confirming what type it is and if I should be able to replace it with MK4015N.

 

Has anyone been able to successfully replace this RAM with some equivalent (other than a donor board)?

Thanks!   

[Middleway]

I have a second Channel F (Model 1) and successfully used 1 of its RAM chips to replace the defective one in the Model 2 and it worked.  So looks like they are interchangeable.  I had ordered a couple of MK4027N chips online but they didn't work, which complicated the troubleshooting.  

 

Still seems strange to me that the Model 2 is supplying +12V to Vcc and Vdd. 

 

[+KylJoy]

I'd like more information on the Fairchild RAM as well.  What can be used as a replacement for teh model 1 and model 2, please?  Anyone?

[+KylJoy]

Some info...

 

For my US NTSC Model I the RAM is labeled "33-9023-00".  I was able to replace the RAM with MK4027 but I had to replace all 4.  Using a mix of the original RAM and the replacement caused issues like graphical glitches, rebooting and other odd behaviors.  I am not sure why this is the case.  Perhaps timing?