Commodore 4046 / Educator64

Good evening gentlemen,

Maybe this is already known but I thought I'd post it as I couldn't find 
it documented anywhere. I recently acquired a Commodore 4064 aka 
Educator 64 in non-working, but excellent cosmetic, condition. Having 
read a few articles on Bo's site and floodgap, I was expecting to find a 
standard 64 board but this one was clearly manufactured specifically for 
the 4064 and was not a refurbished 64 board.

When I was originally saw the pictures, I saw the SID was missing but 
assumed someone had stolen it for other uses or to sell. When it 
arrived, a quick inspection of the mainboard shows that the SID was 
never fitted, along with many other components.

It's a 1st revision 326298 board with the 5 pin AV socket and the the 
following components are missing:

a) The SID, along with the supporting passive components
b) The circuitry to mix in the chroma component from the VIC-II
c) the modulator
d) colour ram, plus the 4066 to allow the CPU to see the colour ram
e) power switch, din socket & power LED passive components

There's then a mod to the board to pull the the outputs of the missing 
4066 at U16 high by a 3.3k resistor so the VIC-II will always see $0F or 
light grey as the character colour. Strangely, the 4066 to switch the 
SID's analogue inputs between the joystick ports is present, which I 
find strange as there's no SID to read them. Is there a reason I'm 
missing why this might be so?

The sync/luma signal is taken direct from the VIC-II to an external 
board which splits out the hsync, vsync and video-on signal expected by 
the PET monitor. This has the effect of black being 'off' and any other 
colour 'on', so no luminance variance. Playing games can be challenging 
but is usually OK if the background is predominantly black. As a test, I 
ran 'Edge of Disgrace' which runs although many of the effects look 
rather unexciting on the PET monitor. On the 326298 board, the composite 
signal is generated outside of the modulator so there is still a signal 
on pin-4 of the AV port which includes the luminance, but the lack of 
the colour RAM still messes up many screens.

I also noted that the 4064 kernal resets the screen & border colours 
back to black as part of the IRQ service routine, I guess to aid 
compatibility of BASIC programs.

Here's a decent picture of the mainboard with a few others one directory 
level up.

http://www.inchocks.co.uk/commodore/4064/4064_MainBoard.JPG

cheers, Rob



       Message was sent through the cbm-hackers mailing list