Help needed with VIC20

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Boydie
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Help needed with VIC20

Post by Boydie » Mon Aug 12, 2019 10:26 am

Flush with my success with the C64, I’m trying to get my VIC working.
At best, it gets to the cyan border with white screen, but no text. The cassette motor generally comes on at this point.
Other times (often as it gets warmer), it has cyan border and white screen, but with lines of pixels scrolling up the white part of the screen (imagine a few lines of text, compressed to one pixel high, then displayed with a dodgy vertical hold). The cyan border is unaffected. The cassette motor does nothing until the white screen area becomes clear (which it sometimes does after a few seconds).
Looking around, the troubleshooting guides don’t point to any individual chip for these symptoms, and there don’t appear to be forums full of advice along the lines of “put the logic probe here” etc.
It *feels* as though the machine is hanging at various points in its reset cycle, but how to check?

Any ideas where to test, or recommendations for forums which will offer stardot-level troubleshooting?

Boydie
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Re: Help needed with VIC20

Post by Boydie » Tue Sep 10, 2019 5:05 pm

Despite the apparent lack of stardot-level assistance out there for Commodore stuff, I managed to get this working.
Turned out to be the Basic ROM. One desoldering of said ROM, fitting a new 24-pin socket, fitting a 2764 into an Ebay-sourced 2764-2364 adapter and Robert's your father's brother! :D

One fully functioning Vic-20 (well VC-20, it seems to be one of the made-in-Germany ones)

roganjosh
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Re: Help needed with VIC20

Post by roganjosh » Tue Sep 10, 2019 6:50 pm

Boydie wrote:
Mon Aug 12, 2019 10:26 am

Any ideas where to test, or recommendations for forums which will offer stardot-level troubleshooting?
The forum->Help&Support section at https://www.lemon64.com is useful for troubleshooting.

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1024MAK
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Re: Help needed with VIC20

Post by 1024MAK » Tue Sep 10, 2019 10:37 pm

I'm not sure there are many Vic-20 owners in this parish :?

Mark

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tricky
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Re: Help needed with VIC20

Post by tricky » Tue Sep 10, 2019 10:45 pm

Well done, my first micro was a vic-20, which was later upgraded with a c64 motherboard and very dodgy PSU. The Vic got hundreds of hours use until I got a beeb, but the c64 only got about 8 hours (playing Uchi Mata) and spectrum about 8 minutes - which I regret a little now.

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