Slow Reset / Video Adjustment

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Bobbi
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Slow Reset / Video Adjustment

Post by Bobbi »

I finally received the power transformer for my PET-style keyboard VIC-20. The machine works very nicely in my brief testing so far - the keyboard looks and feels like it has never been used!! The composite video is also pretty good without any adjustment - certainly much better than my other VIC (a CR model.)

One issue I noticed is that the machine is very slow to come out of power-up reset. It sits with a blank screen for 10 seconds or so before the BASIC signon screen is shown. I believe this is an issue with the reset circuit, which is based on a good old 555 timer. What components should I be looking at replacing? This is a late-1980 NTSC VIC-20, so it is the middle motherboard (not the original VIC-1001 and not the CR-one, but the one in between!) I am assuming it is most likely a bad capacitor ...

My second question is how should I adjust the video to get the best composite output. It looks like the level just needs to come up a bit, but this machine has three trimpots and I don't want to wreck the settings!
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eslapion
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Re: Slow Reset / Video Adjustment

Post by eslapion »

Bobbi wrote:One issue I noticed is that the machine is very slow to come out of power-up reset. It sits with a blank screen for 10 seconds or so before the BASIC signon screen is shown. I believe this is an issue with the reset circuit, which is based on a good old 555 timer. What components should I be looking at replacing? This is a late-1980 NTSC VIC-20, so it is the middle motherboard (not the original VIC-1001 and not the CR-one, but the one in between!) I am assuming it is most likely a bad capacitor ...
The 555 delay capacitor is dying. As I said in the keyboard thread, this machine must have been left unused for a long time so this mean you should also replace the delay capacitor with a new one.
My second question is how should I adjust the video to get the best composite output. It looks like the level just needs to come up a bit, but this machine has three trimpots and I don't want to wreck the settings!
I know how to do that with a scope with I am working on something simpler.
Be normal.
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