jim@ghp.UUCP (Jim Stewart) (02/19/90)
I have an old CGA that I am trying to get working with the composite input to my colour TV. Before everybody says "why", it started as a project to get a cheap machine going for my kids, age 8 and 5. If they destroyed it it wouldn't be a big loss. BUT! Now unfortunately it has become a matter of my sanity. I might even spend the money to buy a better monitor, etc., but first I going to get the #@%&$%! thing working. The current system works fine, on a monochrome composite monitor. It also works in black and white through the video input on the colour TV (i.e., I display a game I know is in colour, but I only get grey and white). I have looked at the composite output from the board. I can see the colour burst, I can see the colour modulation, I think I have the right levels, the colour burst frequency is in the right range (pretty lousy accuracy from a scope). I talked to an engineer that used to manufacture televisions. He said to be sure of several parameters, but as I pressed he didn't leave me comfortable. What are the critical details of NTSC with respect to colour? I can post the parameters I measured if that helps. Maybe my CGA clone was never intended to do composite colour, the RCA phono was only there for good looks, but I need to know why before I can let it go. I've spent about a month on this so far, so any help will be appreciated. tnx -- Jim Stewart, VE3SRJ UUCP: jim%ghp@mnetor.uucp BELL: (416)862-0430
ardai@bass.bu.edu (Michael Ardai) (02/21/90)
In article <507@ghp.UUCP> jim@ghp.UUCP (Jim Stewart) writes: >I have an old CGA that I am trying to get working with the composite >input to my colour TV. [Color screens show up as BW on the TV] >-- >Jim Stewart, VE3SRJ >UUCP: jim%ghp@mnetor.uucp >BELL: (416)862-0430 I had this problem on an old clone. In my case, the 14.xxx oscillator on the motherboard was slightly off. There may be a trimcap either near the expansion connectors or the CPU that adjusts the frequency. Run a color program on the PC and slowly turn the cap (in both directions) until the color locks in. Use a non-metallic screwdriver since hand capacitance will de-tune the cap. /mike \|/ Michael L. Ardai ...!sun!teraida!maven.DECNET!ardai (preferred) --- ---------------------------------------------------------------------------- /|\ ardai@bu-pub.bu.edu
s37750u@kaira.hut.fi (Niclas"nikke"Ek) (02/21/90)
If got 9 pinns cannon connector in your CGA-card I may help you...It would be nice if had allso scart- connector in your tv-set(not a must!).I have scematics on circuit which CGA signals to vidio composite... If this is what you need send me your address and you will get scematics free...my elm address is in sender... hope I could help you!!!
king@dciem.dciem.dnd.ca (Stephen King) (02/21/90)
In article <52494@bu.edu.bu.edu> ardai@bass.bu.edu (Michael Ardai) writes: >In my case, the 14.xxx oscillator on the motherboard was slightly off. That is 14.31818 MHz. For best results use a frequency counter. Look at the colour burst. Make sure that at least 7 or 8 cycles of the subcarrier are transmitted during the burst (you'll probably need a scope with TV sync option). Subcarrier tolerences are very tight. It must be 3579545 Hz.
michael@fe2o3.UUCP (Michael Katzmann) (02/22/90)
In article <507@ghp.UUCP> jim@ghp.UUCP (Jim Stewart) writes: >I have an old CGA that I am trying to get working with the composite >input to my colour TV. >It also works in black and white through the video input on the colour >TV (i.e., I display a game I know is in colour, but I only get grey >and white). I have looked at the composite output from the board. >I can see the colour burst, I can see the colour modulation, I think >I have the right levels, the colour burst frequency is in the right >range (pretty lousy accuracy from a scope). > >What are the critical details of NTSC with respect to colour? I can >post the parameters I measured if that helps. The colour burst frequency must be spot on! The receivers colour subcarrier oscillator must be able to lock on to it. The burst must be in the right position (5.3us after leading edge of sync). Also the level of the burst must be right or the set will operate the colour killer. (It should be abt 40 IRE units P-P (Whole signal is 140 units sync-tip to peak white + chroma). --------------------------------------------------------------------- email to UUCP: uunet!mimsy!{arinc,fe203}!vk2bea!michael _ _ _ _ Amateur | VK2BEA (Australia) ' ) ) ) / // Radio | G4NYV (United Kingdom) / / / o _. /_ __. _ // Stations| NV3Z (United States) / ' (_<_(__/ /_(_/|_</_</_ Michael Katzmann Broadcast Sports Technology. 2135 Espey Ct. #4 Crofton Md. 21114 USA Ph: +1 301 721 5151