Schema wrote:
Does anyone know more about this, and which potentiometer it might be?
Orginal Vic-20 schematic shows video level control adjustment pot as R7
There will be two adjustable controls under RF shield (covering 6560 chip). The device labeled as C55 (or C48 for cost reduced board) is fine tune adjustment for TTL clock driving 6560 chip and should not be altered.
I pulled apart a cost reduced Vic-20 this afternoon and adjusted video level control (appears to be labelled as R10 on cost reduced board).
This will work to fix low video level on Commodore monitors.
My schematic for non cost reduced model also shows an additional pot R32. This pot sets the forward bias on common emitter buffer/amplifier Q7. This will establish black level setting. The extra pot is not present on cost reduced model and was likely replaced with fixed value resistor.
Hope this helps.
Mega-Cart: the ultimate cartridge for your Commodore Vic-20
Schema wrote:Does anyone know more about this, and which potentiometer it might be?
There is only the one variable resistor. On the older two prong power Vic it adjusts the black level and on the later C64 type powerd Vic it only adjusts the luminance level, the chroma is unaffected.
No real harm in trying to adjust either but I'd mark where they are to start before atempting any adjustment. (Well no, I wouldn't, but then I have the kit to view the output waveform set them up properly. If I didn't have that I'd mark them first, honest. 8^)= )
I wonder if that adjustment will make the RF modulator give a better signal too? I find that my older TV is noisy. (I even tried a couple different RF modulators with similar results). Its not dark though, just quite noisy. Yet a VCR on the TV is clear.
Is the border green on this VIC, or is this a side effect of the photography?
bbell wrote:I wonder if that adjustment will make the RF modulator give a better signal too? I find that my older TV is noisy. (I even tried a couple different RF modulators with similar results). Its not dark though, just quite noisy. Yet a VCR on the TV is clear.
Video level adjustment will not resolve noisy picture problem.
- check to ensure all connections are tight
- if using old TV, check balun (75 ohm to 300 ohm adapter)
- if using old TV - try fine tuning adjustment
- check cables
- check coax
Mega-Cart: the ultimate cartridge for your Commodore Vic-20
bbell wrote:Is the border green on this VIC, or is this a side effect of the photography?
The cyan became more greenish as I cranked up the video level.
Actually, now I have the opposite problem as before. With the video level cranked high enough that it looks good on the 1702 monitor, my VCR/TV refuses to display it. Found a reasonable compromise for the level though. Or I could set up one VIC for TV/VCR display and the other for the monitor
I've actually found different revisions of the VIC-20 vary slightly in quality in terms of visual output, though the best monitor is the 1901-types with the AV input on the front. SCART leads can also be made up, and look great on my wide-screen TV (although it's still a CRT and not LCD or anything like that).
The C=VGA project is still in development, and it is Allan's intention that it will be able to output all out computer signals (with the exception of those that can only output RF) to a VGA compatible monitor. Hopefully, a prototype is on it's way and then testing can begin.
Great tip with the potentiometer, now all of my VICs have a very bright and clear display
By doing the adjustments I found out that the two prong models I have are cost reduced and the one with the DIN plug is an older version. I always thought it would be the other way around and that the DIN power would have started with the C64 aera. So why in the world did commodore change the power supply in the middle of production and why got the C64 the "older" power supply? This seems to be unlogical for Commodore, supporting two different power supplies which only can lead to confusion and extra costs...
Schema wrote:Thanks! I just tried it and it worked a treat.
I tried it too and it worked the same for me. My VIC looked the same as yours before and now it looks bright and "normal". I'm using a 1701 monitor too, but I wonder, why are you plugging the video (or is that the audio) into the front of the monitor instead of the back?
I have the official monitor cable for the VIC 20 but I find that it only uses 2 of the 4 RCA connectors provided....this sounds strange but it works - you would think it needs both a chroma and luma connectors to be plugged in, but I guess these are combined in the VIC beforehand. If I plug the connector into either the Chroma or Luma plugs on the back of the 1701, I get a nice colour picture....
Yes, the VIC-20 video output is composite, doubled on two pins with a different resistance (at least on some models). Internally, the VIC chip seems to have output for luma and chroma, but it gets mixed before the output. If I had a lot of VICs and good electronical skills, I might try to tap the signals from the chip to see if one can get a such separate video signal.
Schlowski wrote:
By doing the adjustments I found out that the two prong models I have are cost reduced and the one with the DIN plug is an older version. I always thought it would be the other way around and that the DIN power would have started with the C64 aera. So why in the world did commodore change the power supply in the middle of production and why got the C64 the "older" power supply? This seems to be unlogical for Commodore, supporting two different power supplies which only can lead to confusion and extra costs...
Björg
What??? That can't be right. How did you come to that conclusion?
PRG Starter - a VICE helper / Vic Software (Boray Gammon, SD2IEC music player, Vic Disk Menu, Tribbles, Mega Omega, How Many 8K etc.)
Something I just noticed. I went and bought all of the stuff to make my own cable for the vic to hook to a 1702 monitor. I had a wire to the video high one to video low and one to the audio on a 5 pin din(CB's and midi stuff if you have trouble finding one.)The sound worked. The video didn't work. I connected to 2 videos together and that didn't work. I was getting frustrated unplugging wires and plugging them back in again, changing the nobs on the monitor. I could see a faint picture but could do nothing about it. I tried once more, unplugging the rca plugs to check my soldering, and plugged them back in and missed the hole for the audio and it hit the outside metal ring of the rca jack. Bing-bong there was the picture. WHat?!? I hooked the wires up to the right pins on the din plug. I held the center pole to the metal ring and tried the sound test again. Every time the a sound was supposed to come out of the speaker, the picture flickered. To make a long story short the video must be grounded. I used an extra wire from the video rca ground to pin 2 on the dim. It works great now. I guess the sound is grounded in the montor somehow. This sounds like the same problem you're having. I'm thinking the VCR might be grounding the video for you(That's why it worked threw the VCR). Just thought I'd share some of my woes with you.
