Questions about a vic 20

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Pandacorvette
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Questions about a vic 20

Post by Pandacorvette »

So i am new here and got a free vic 20 with a 1541 disc drive. the drive works. but the vic doesn't
So I bought a vic 6560 online. and I found that the vic 20 has a 6560-101 :shock:. . I know ones pal .but are they interchangeable with each other or do I need to do something to get it to work. I am fairly new to old computers to. but I'd like to see it working.


rmzalbar
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Re: Questions about a vic 20

Post by rmzalbar »

6560-101 is NTSC. PAL VIC is 6561-101. If your chip is missing the -101, it could be an early revision or it could have been remarked by a Chinese recycler, but it shouldn't matter. Just replace 6560 with 6560 and 6561 with 6561 without regard to any suffix.
http://sleepingelephant.com/denial/wiki ... nology_VIC
https://en.wikipedia.org/wiki/MOS_Techn ... IC_IC_list

PAL and NTSC are not interchangeable because of clock difference. This shows how to do it, but it's not exactly a reasonable thing to do unless you have no other option:
http://a1bert.kapsi.fi/Dev/PAL2NTSC.html

Note that composite video is the output, so you need to have the proper PAL or NTSC monitor to get color in that format. I guess many LCD TVs with composite inputs actually can decode both.

Once it's working, you should adjust the video gain and bias trimpots for a good picture. The factory tuning is meant to drive an RF converter, and looks dim when the composite is used directly:
http://sleepingelephant.com/denial/wiki ... djustments
banman
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Re: Questions about a vic 20

Post by banman »

Hi Pandacorvette and rmzalbar,

Good on you for giving the Vic 20 machine a go! :D

Could you tell us a little bit more about your Vic 20?

Do you have photos of the serial number label attached on the underside of the computer as well as a main board photo? That's an easy way to tell if it's an NTSC or PAL machine. If it's made in the USA it a sure thing it's NTSC. If it's made in Europe or Japan it is probably a PAL standard.

Watch some of those sellers, rmzalbar is right. They get someone else's ewaste and sell it on as new stuff.

I personally don't mind as long as they're honest and upfront about its condition. I have bought chips that have been re labelled as looking in the seller's mind as being new.

This gentleman's website is great if you want to check if the Vic video chip is operating or not. If the video chip is good there may be problems with one of the 3 ROM chips on the main board (character,Kernal, and BASIC) stopping the Vic 20 from booting. The Vic 20 machines are much tougher than the C64 machines.

https://forums.overclockers.com.au/thre ... n.1220403/

I imagine that it could be tested with a cheap logic probe. All one is looking for is clock out signal/ activity.

I shamelessly lifted a mainboard image from here https://lyonsden.net/wordpress_s/wp-con ... scaled.jpg

VIC20-Motherboard-scaled.jpg





I personally bought a 6560-101 (NTSC) Video chip from an AliExpress seller and used the above method to determine the chip was gone. I immediately raised refund claim (they call it a dispute). They happily refunded my money and I reordered another one from the same seller.
This second one tested good thankfully.
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