View Full Version : Need help with VIC-20 Diagnostics Cart

November 22nd, 2008, 03:40 PM
Hey everyone,

Does anybody have the VIC-20 Diagnostics Cartridge? If so, do you have instructions and dongles with it? I can't find instructions or schematics for the dongles anywhere and would like to build some.

If you have the stuff but can't scan it or pinout the dongles, I'd be happy to do that and pay you back for the shipping costs. It'd be nice to have it documented somewhere on the web.

Also, I'd like to find a schematic for it or at least pics of the top & bottom of the board to make sure I have the one I built on the right board.

I downloaded 2 different ROM images and have tried both but all I get are random ROM errors. Nothing is repeatable and it is frustrating. I've tried it on multiple boards and have swapped out known good ROMs but still get ROM errors at random places.



November 22nd, 2008, 05:57 PM
As a matter of fact, the VIC-20 diagnostics cartridge was discussed on the Denial forum just recently.


I'm not sure if that discussion will be of any help to you.

November 22nd, 2008, 07:33 PM
That was VERY helpful :D

I knew the memory was on there somewhere but couldn't figure out where!

I had a Kantronics cart board that was made for a 24 or 28 pin EPROM. I stripped the 24 pin socket, soldered in a 6264 SRAM and had it wired to Bank 1. I also cut a trace on pin 31 (it was tied high) and wired it to RW. That worked and I had 8K of extra memory...

Next I soldered the EPROM on top of the SRAM and connected pin 18 to Bank 5*... the diagnostics would come up but still screw up.

Once I moved the connection on pin 20 of the SRAM from Bank 1 to RAM 1 the cart worked like a dream. It's an 8K chip, but only the first 1K of it is in use. ;)

Now to build the loopback plugs!

I figured it would be over on the Denial board but nobody would ever approve and activate my account over there. It's frustrating to have a board I can't use. :confused: :confused: :confused:

Anyway - THANK YOU for the help!


November 22nd, 2008, 08:34 PM
Never mind!

I found the shoutbox on the Denial website and put in a request to have my account activated and it's now good to go!