Bryan Posted May 14, 2013 Share Posted May 14, 2013 Yeah right... :-( That kind of ghosting is caused by an impedance mismatch and reflections within the video cable. If you use a longer cable, you'll see the ghosting move farther to the right. Quote Link to comment Share on other sites More sharing options...
biobern Posted May 14, 2013 Share Posted May 14, 2013 That kind of ghosting is caused by an impedance mismatch and reflections within the video cable. If you use a longer cable, you'll see the ghosting move farther to the right. At the moment, I use a thin "audiolike" video cable like most cheap video cables are today. Length is 2,20m. I just found an old fat video cable with BNC plugs, labelled with "50 ohm". Do you think this is a solution? Quote Link to comment Share on other sites More sharing options...
BillC Posted May 14, 2013 Share Posted May 14, 2013 At the moment, I use a thin "audiolike" video cable like most cheap video cables are today. Length is 2,20m. I just found an old fat video cable with BNC plugs, labelled with "50 ohm". Do you think this is a solution? The 50 ohm cable you found is most likely an old co-ax network cable, they had 50 ohm impedance and used BNC connectors. Quote Link to comment Share on other sites More sharing options...
biobern Posted May 15, 2013 Share Posted May 15, 2013 The 50 ohm cable you found is most likely an old co-ax network cable, they had 50 ohm impedance and used BNC connectors. Yes, you are right. But google told me that cables with 50 ohms are used for video also. In fact, the old Sony monitor has switchable terminators labeled with 75 ohms. Maybe I should try a cable with 75 ohms? I never understood that wave impedance thing. Quote Link to comment Share on other sites More sharing options...
Bryan Posted May 15, 2013 Share Posted May 15, 2013 When you put signals on a length of wire, the potential on the wire is not instantly the same everywhere. Instead, it travels down the wire like a wave until it reaches the other end. This happens very quickly and is negligible when dealing with slow-changing signals (like audio) but with fast signals (like radio and video) you have to treat the cable as a transmission line where energy can bounce back and forth like waves in a tank of water. The ghosting you see is the 2nd arrival of the signal after some of the energy bounced back up the cable. Impedance matching means designing a circuit that not only achieves the desired voltage (amplitude) of the signal but also the correct source impedance for the cable and load (monitor) which will be used. When proper matching is used, the waves pass through each connection in the circuit efficiently. http://en.wikipedia....edance_matching 1 Quote Link to comment Share on other sites More sharing options...
biobern Posted May 15, 2013 Share Posted May 15, 2013 I tried a very short (50cm) 50 ohms cable and a longer 75 ohms cable now. Also tried different grounds and so on. All useless. So, the problem is the simplicity of the circuit and my unforgiving old CRT monitor. Seems that I have to wait for a better circuit. Off topic: At least my brandnew 48K RAM extension works perfect. That means that SIO2SD works too. _That's_ good news! Quote Link to comment Share on other sites More sharing options...
Bryan Posted May 15, 2013 Share Posted May 15, 2013 I am rather surprised that a 50cm cable is showing the problem. It usually shows up with longer cables. Does the ghosting look different when you swap cables? Quote Link to comment Share on other sites More sharing options...
biobern Posted May 15, 2013 Share Posted May 15, 2013 I am rather surprised that a 50cm cable is showing the problem. It usually shows up with longer cables. Does the ghosting look different when you swap cables? No, exactly the same ghosting and all the other strange effects with all 3 cables. Quote Link to comment Share on other sites More sharing options...
Bryan Posted May 15, 2013 Share Posted May 15, 2013 No, exactly the same ghosting and all the other strange effects with all 3 cables. Well then it's a bit of a mystery. Maybe the 4050 is ringing under the load. Perhaps switching it to a more modern HC version would stop it. (although, the picture looks like classic impedance problems- multiple after-images that fade) Quote Link to comment Share on other sites More sharing options...
Magic Knight Posted May 15, 2013 Author Share Posted May 15, 2013 (edited) Ok I rigged up a Composite hot-wire and with little attention to shielding etc, i got reasonable results: ( click the pictures to enlarge) you may want to place a variable resistor in series with the Luma one as Atari's do vary. I tend to notice only differences as a 'brightness' level but it may help prevent ghosting where there is a problem by adjustment to the signal strength on this leg. ive used absolutely no screening and its a hotwire nightmare (deliberate ) as - i dont personally think the immediate issues with the screening where this is the absolute issue, i think the luma value may need to be adjusted to be sure, in anycase. The effects i have got may improve with proper screening, but its not the main cause as far as i can see. ps - this composite piece does look 2nd class compared to S-video and you may want to consider splashing out $15-$25 for a decent crt monitor (on Ebay) as the affordability and clarity you get is rewardable. Edited May 15, 2013 by Magic Knight Quote Link to comment Share on other sites More sharing options...
biobern Posted May 15, 2013 Share Posted May 15, 2013 Ok I rigged up a Composite hot-wire and with little attention to shielding etc, i got reasonable results: you may want to place a variable resistor in series with the Luma one as Atari's do vary. I tend to notice only differences as a 'brightness' level but it may help prevent ghosting where there is a problem by adjustment to the signal strength on this leg. ive used absolutely no screening and its a hotwire nightmare (deliberate ) as - i dont personally think the immediate issues with the screening where this is the absolute issue, i think the luma value may need to be adjusted to be sure, in anycase. The effects i have got may improve with proper screening, but its not the main cause as far as i can see. ps - this composite piece does look 2nd class compared to S-video and you may want to consider splashing out $15-$25 for a decent crt monitor (on Ebay) as the affordability and clarity you get is rewardable. You have very good quality! Wow! A variable resistor will not help for me. I also tried 100 ohms and 150 ohms instead of 75 ohms. Always the same crap. I definately will try other CRT monitors, but I have to buy one. At the moment, the Sony is my only CRT that is able to display NTSC. I live in germany you know. Quote Link to comment Share on other sites More sharing options...
Magic Knight Posted May 15, 2013 Author Share Posted May 15, 2013 You have very good quality! Wow! A variable resistor will not help for me. I also tried 100 ohms and 150 ohms instead of 75 ohms. Always the same crap. I definately will try other CRT monitors, but I have to buy one. At the moment, the Sony is my only CRT that is able to display NTSC. I live in germany you know. try 50 ohms or 30, this may make a difference perhaps, Quote Link to comment Share on other sites More sharing options...
biobern Posted May 15, 2013 Share Posted May 15, 2013 ps - this composite piece does look 2nd class compared to S-video and you may want to consider splashing out $15-$25 for a decent crt monitor (on Ebay) as the affordability and clarity you get is rewardable. I just tried an old Apple II monochrome green monitor on my Atari. No ghosting, great picture. But monochrome is not what you really want. Just a little test...... Quote Link to comment Share on other sites More sharing options...
mimo Posted May 16, 2013 Share Posted May 16, 2013 If you use any Atari in mono it looks great, just when you add the chroma signal it all goes wrong Quote Link to comment Share on other sites More sharing options...
iratasan Posted May 17, 2013 Share Posted May 17, 2013 This looks like a S-vid / Composite hybrid. which do you prefer? or are you rigging this up to have the switch over option to have both? No, i do not need to have both. S-Video output would be fine. Just not sure if the instructions i linked are somehow outdated or can ben trusted, it's been a while since i got them. Quote Link to comment Share on other sites More sharing options...
Magic Knight Posted May 17, 2013 Author Share Posted May 17, 2013 No, i do not need to have both. S-Video output would be fine. Just not sure if the instructions i linked are somehow outdated or can ben trusted, it's been a while since i got them. From the kit supplied (and to make it simple to get results) you will need to connect the luma from the 400 to the 74 ohm resistor and the out of this goes to the monitor (on luma). The chroma from the 400 goes to the positive on the capacitor and the part marked "-" goes to the output which goes to the monitor (chroma). The ground from the 400 goes to the ground on the monitor the other switches/resistors etc are not essential to get a sharp s-video on your monitor. locate these compontns and use the 3 primary parts to get a decent signal. For audio - connect the ground from the 400 to both the signal ground and audio ground. connect the audio signal to the audio signal to your monitor, with exception of the grounds there should be absolutely no interconnectivity between the luma/chroma/grnd. (in my strongest opinion - grounding via a resistor doesnt make any real difference with proper screening in place (i ve done this with 6 ataris 2 x 400's, 2 x 600xl, 800xl & 65XE - it should be ok with all ataris with this). Quote Link to comment Share on other sites More sharing options...
biobern Posted May 17, 2013 Share Posted May 17, 2013 ps - this composite piece does look 2nd class compared to S-video and you may want to consider splashing out $15-$25 for a decent crt monitor (on Ebay) as the affordability and clarity you get is rewardable. Yesterday, I bought a Sony 21" Trinitron CRT television that is only 10 years old for 20 €. Maybe 20 years newer than my good old Sony 21" monitor but with very similar features from my point of view as a retro collector. It should do NTSC also, but does not autodetect my Atari 400 composite as a proper NTSC signal. So, I have no colors, just greyscale. It's also not possible to kinda force NTSC colors in the service menu, so the problem persists. In fact, I have the exact same problem sometimes with my 30 years old Sony monitor! DAMN! :-(((( Haven't tried S-Video yet. Should work with my new Sony. I will try in the next days..... Quote Link to comment Share on other sites More sharing options...
Bryan Posted May 17, 2013 Share Posted May 17, 2013 I just tried an old Apple II monochrome green monitor on my Atari. No ghosting, great picture. But monochrome is not what you really want. Just a little test...... Does your composite monitor display other sources clearly? Quote Link to comment Share on other sites More sharing options...
biobern Posted May 17, 2013 Share Posted May 17, 2013 Does your composite monitor display other sources clearly? Im not sure witch monitor you mean here but yes, all my monitors display all my composite sources clearly. The only problem is kjmann-composite in my Atari 400. Quote Link to comment Share on other sites More sharing options...
Magic Knight Posted May 17, 2013 Author Share Posted May 17, 2013 If you give me the model number (of both monitors) , i can check the specs... Quote Link to comment Share on other sites More sharing options...
biobern Posted May 18, 2013 Share Posted May 18, 2013 (edited) If you give me the model number (of both monitors) , i can check the specs... Trinitron from the 80s: Sony PVM-2010QM (Name of the Chassis: SCC-557A-A) Trinitron from the 00s: Sony KV-21M1D (Name of the Chassis: BE-4A) Edited May 18, 2013 by biobern Quote Link to comment Share on other sites More sharing options...
Bryan Posted May 18, 2013 Share Posted May 18, 2013 Im not sure witch monitor you mean here but yes, all my monitors display all my composite sources clearly. The only problem is kjmann-composite in my Atari 400. I believe the monitor's input is being over-driven and some monitors have more tolerance for it. Looking at the LUM resistors (120, 240, 510) it's clear that this upgrade can provide about a 65-ohm path to 5V which will deliver too much voltage to a composite input, even with the 75-ohm inline resistor. Also, why are there only 3 add-on resistors when there are 4 LUM signals (LUM0-LUM3)? Do GTIA modes look normal? Anyway, the entire composite video signal should fit within a 1V range. So, if we assume 4.5-5V out of the 4050, then the combined resistance of all LUM signals needs to be about 330 ohms. This would provide around 2V max to the 75-ohm output resistor and then it gets dropped by half by the monitor's internal 75-ohm resistor. I would try values of 3.9K (LUM3), 2K, 1K, and 510. Quote Link to comment Share on other sites More sharing options...
biobern Posted May 18, 2013 Share Posted May 18, 2013 I would try values of 3.9K (LUM3), 2K, 1K, and 510. I'd like to try. But I don't know which Pins LUM0-LUM3 are, sorry. Would you please write it for the stupid. Something like "3.9k instead of XXX ohms, 2k instead of YYY ohms....." Thanks.... Quote Link to comment Share on other sites More sharing options...
Bryan Posted May 18, 2013 Share Posted May 18, 2013 Getting out the hardware docs.... on the 400, these are the video 'ladder' resistors: LUM0 - 62K R180 - 2K LUM1 - 30K R178 - 1K LUM2 - 12K R177 - 470 or 510 LUM3 - 120K R179 - 3.9K SYNC - 15K R176 - 510 (I don't know their relative positions) This gives a combined resistance of 172. So, if we ignore the 4050's internal resistance, we get a voltage swing of 2.3V which will translate to 1.15V as seen by the monitor. In reality, it will be little lower since the 4050 won't go rail to rail. If it looks a little dark, the 75-ohm output resistor can be reduced. 1 Quote Link to comment Share on other sites More sharing options...
biobern Posted May 19, 2013 Share Posted May 19, 2013 Yesterday, I bought a Sony 21" Trinitron CRT television that is only 10 years old for 20 €. Maybe 20 years newer than my good old Sony 21" monitor but with very similar features from my point of view as a retro collector. It should do NTSC also, but does not autodetect my Atari 400 composite as a proper NTSC signal. So, I have no colors, just greyscale. It's also not possible to kinda force NTSC colors in the service menu, so the problem persists. In fact, I have the exact same problem sometimes with my 30 years old Sony monitor! DAMN! :-(((( Haven't tried S-Video yet. Should work with my new Sony. I will try in the next days..... I tried S-Video today. No color! Again, the new television does not recognize this as a proper NTSC signal. :-( Quote Link to comment Share on other sites More sharing options...
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