24 euro VIC-20

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mrr19121970
Vic 20 Nerd
Posts: 873
Joined: Tue Jan 19, 2016 9:22 am
Location: Germany
Occupation: IT service manager

Re: 24 euro VIC-20

Post by mrr19121970 »

Yesterday I scraped off the paint and rust on the sideplate. It is now soaking in vinegar to remove the final rust traces. Does anyone know which RAL code to use to paint the sideplate? Any recommended brands?
Kakemoms
Vic 20 Nerd
Posts: 740
Joined: Sun Feb 15, 2015 8:45 am

Re: 24 euro VIC-20

Post by Kakemoms »

mrr19121970 wrote:I had a closer look at the board yesterday to update this thread and observed the 2 CIA chips had different date codes. One was late 1984 which was substantially older than all other chips on the board. This indicates to me a (professional) repair either under or out of guarantee - maybe also why so many chips are socketed too (the soldering is 'factory quality')
Funny thing is that early versions of the VIA chips (which is what you have) had several bugs, especially the shift register bug which caused commodore to slow down the Vic-20 and 1540/1541 serial bus. I am not sure when they fixed this bug, but apparently they became aware of this during the early stages of the Vic-20 production (1980/1981). So there is a slight possibility that the 1984-version of the VIA is made with a different set of masks (e.g. transistor layout). If these guys continue their work we may finally find out.

The bug is fixed in all versions of the CIA, but due to "backward compability" they chose to continue with their slow serial bus implementatio (nuts!).
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mrr19121970
Vic 20 Nerd
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Joined: Tue Jan 19, 2016 9:22 am
Location: Germany
Occupation: IT service manager

Re: 24 euro VIC-20

Post by mrr19121970 »

Yesterday I was using this vic20 as a test harness for another one with a black screen. It ideal as is mainly socketed.

I got to testing via1 and it didn't work. Then I put the original back in and also this didn't work either anymore. Damn. Broke a working vic to save another. I decided this couldn't be right so tested both via in a 3rd vic. Works. Strange. Time to get out the multimeter. I found pin 23 had nothing from the chip leg to the back of the board. I desoldered the (factory ??) Installed socket. Low and behold about 4 legs where missing. I assumed now insidie my desoldering gun chamber. New socket in and working again.
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