Older Model Vic-20: Glitchy Graphics
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Older Model Vic-20: Glitchy Graphics
Hi there!
I'm new to the forum and have a question regarding one of my VIC-20 computers. The one I like to use is an older model, and everytime I start it up I get crazy looking letters and characters all over the screen and in different colours as well. The background colour is still the cyan colour it's supposed to be.
When I shut down and power back on, the characters appear again in the EXACT same locations on screen. It never changes. Any ideas on what it could be and how it can be fixed?
Thanks for reading.
I'm new to the forum and have a question regarding one of my VIC-20 computers. The one I like to use is an older model, and everytime I start it up I get crazy looking letters and characters all over the screen and in different colours as well. The background colour is still the cyan colour it's supposed to be.
When I shut down and power back on, the characters appear again in the EXACT same locations on screen. It never changes. Any ideas on what it could be and how it can be fixed?
Thanks for reading.
According to Ray Carlsen's VIC-20 Diagnostics and Repair article there's a good chance it's the VIC chip (6560 if you're in NTSC-land, 6561 for PAL systems). If so, the only remedy is to get a new VIC chip.
Bacon
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Das rubbernecken Sichtseeren keepen das cotton-pickenen Hands in die Pockets muss; relaxen und watschen die Blinkenlichten.
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Das rubbernecken Sichtseeren keepen das cotton-pickenen Hands in die Pockets muss; relaxen und watschen die Blinkenlichten.
Done some further tests and it appears that game carts also do not work (still has garbage text around but it changes depending on the cart inserted). I'm thinking it's a RAM problem, too...
Since I'm here, I might as well post another Vic-20 problem I have (newer model). I use the same RF Modulator and same hook-up on the older Vic (from above post) for the newer one, and I can't get anything on the screen. Just lots of horizontal white bars and lots of buzzing noises coming from the TV. Oncve and a while I'll see a bit of colour flash across, it's like it's trying to work but it's being interfered with. It's weird because the same connection works fine with the older VIC that produces garbage text.
I was thinking this newer one may have a problem with the Vic Chip...
Since I'm here, I might as well post another Vic-20 problem I have (newer model). I use the same RF Modulator and same hook-up on the older Vic (from above post) for the newer one, and I can't get anything on the screen. Just lots of horizontal white bars and lots of buzzing noises coming from the TV. Oncve and a while I'll see a bit of colour flash across, it's like it's trying to work but it's being interfered with. It's weird because the same connection works fine with the older VIC that produces garbage text.
I was thinking this newer one may have a problem with the Vic Chip...
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- Vic 20 Hobbyist
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Sounds like you need to cobble together a test cart.
That test cart has some RAM of it's own in it that it uses to keep track of the test results and scratchpad info just in case the RAM on your system is hosed.
RJ
That test cart has some RAM of it's own in it that it uses to keep track of the test results and scratchpad info just in case the RAM on your system is hosed.
RJ
Call me a cheap bastard... I learned to fix things to save money... even surface mount soldering...
Visit my website: http://www.arcadecomponents.com
Visit my website: http://www.arcadecomponents.com
Just replaced half an hour ago. No difference. I'm wondering if it's this:Bacon wrote:According to Ray Carlsen's VIC-20 Diagnostics and Repair article there's a good chance it's the VIC chip (6560 if you're in NTSC-land, 6561 for PAL systems). If so, the only remedy is to get a new VIC chip.
UB6 LM555 TIMER POWER-ON SYSTEM RESET
Will not reset on power up. May produce garbled or random screen
characters-graphics, or screen may start up "frozen". If drive resets when
computer is powered up, this chip is OK.
OK, so I've got the soldering iron out and going to do some chip removal.
A question though: Can parts from the 2 different models (old and new) work in each other? Particularily RAM chips?
As you may know based on my other thread, I have 2 Vics down and want to get at least one up and running. Right now, my older model VIC can get a picture, so I'm going to perform surgery and take parts from my newer Vic.
A question though: Can parts from the 2 different models (old and new) work in each other? Particularily RAM chips?
As you may know based on my other thread, I have 2 Vics down and want to get at least one up and running. Right now, my older model VIC can get a picture, so I'm going to perform surgery and take parts from my newer Vic.
The 555 is a pretty durable chip. If a reset problem exists, I would suspect 10uf timing capacitor rather than the 555.ral-clan wrote:The 555 chip is cheap and common, so it's worth swapping it to see if it's the cause of the problem.
Mega-Cart: the ultimate cartridge for your Commodore Vic-20