VIC-20 Schematics

[Stevent281]

I have a Programmers Reference guide that I purchased with my original VIC-20. It was a beautifully draw (machine?) schematic that was very easy to read. That schematic matches my original VIC that I had as a child.

Fast forward to today, I have a VIC that I purchased on eBay. Its a CR with a 324003 motherboard.

I was able to locate schematics online that say they are for the 324001 and/or 324003. Looking at this closely, they seem to be the same.

The VIC-20 Visual history does not list a 324001.

While I have the schematics for the 324001/324003, they look hand drawn and the best version I have is hard to read.

Was there a later version of the Programmers Reference Manual that had the schematic for the VC motherboard?
Or is there a super clean version that is easier to read?

Thank you for your help,
Steve

[Mike]

Welcome!

I have a Programmers Reference guide that I purchased with my original VIC-20. It [contains] a beautifully drawn (machine?) schematic that was very easy to read.

Well, that is somewhat strange. At least the PRG as can be downloaded from DLH/Bombjack does not feature any schematics. The Technical Manual though does, for both the 324001 (2-prong) and 251027 (CR - DIN plug) ASSY.

There also exists a "Schematic Main Logic Version E" which has the sole 74LS133 chip referenced to as UA1, and which corresponds to the 1001006 ASSY of the very first VIC-1001 mainboard. This one indeed looks rather clean and not exactly like "handdrawn".

I have a VIC that I purchased on eBay. It's a CR with a 324003 motherboard.

That's strange once again. The CR mainboard is - as I wrote above - being referenced as 251027 in the TRM.

You might find some small differences to the schematics, especially in the A/V amplifier circuit. Later CR mainboard revisions have the 1K resistor going from the Y pin of the cartridge expansion port to the audio amplifier incorporated as trace. Earlier CR boards feature a bodge wire with the 1K resistor in a heatshrink tube.

[...] the schematics for the 324001/324003 [...] look hand drawn and the best version I have is hard to read.

They're still the originals, and I actually prefer them over reproductions as I know where the errors in the originals are.

Greetings,

Michael

[Stevent281]

Michael, thank you so much for the information.

It was definitely the PRG that I had as a kid, I still have it all. And the schematic that is has is the MAIN LGOIC BOARD VERSION E

Thank you for the link to the DLH archive, I didn't know that existed. I have a scanned copy of the PRG also like the one on DLH and if you look at the table of contents is says the last page is a schematic. Its a fold out so it is about 20" x 14"

I was just curious if a later version of the PRG had updated schematics. The one in the book is very clean and easy to read.

And thank you very much for pointing me in the direction of the VIC-20 Technical Manual. I hadn't found that before, its the first book with reference to the 324003 board.

If you haven't seen it, check out A Visual History. Its a very detailed book with great photos.
https://retrocomputingforum.com/t/commo ... ition/1099

Thank you again,
Steve

[chysn]

I was just curious if a later version of the PRG had updated schematics. The one in the book is very clean and easy to read.

I don't think they ever changed it. I have the PRG First Edition Fourth Printing (1982) and First Edition Sixth Printing (1983), and they both have the fold-out Main Logic Board Version E schematic in the back. I've never seen a Second Edition.

When I was a kid, buying the PRG was a huge investment for me. By the end of the VIC-20's run, PRGs were in the local bookstore's bargain bin for two bucks, so I picked up a spare. Other than printing numbers, they're identical.