MediaPortal Forum - View Single Post - How to improve TV-OUT quality

AberDino · 2005-10-28, 11:15

The 'TV-Out' quality issue seems to come back every so often, and understandably so. I have a Philips 32PW9525 100Hz widescreen CRT television set, which is about 5 years old now. I'm using a dedicated HTPC with a Radeon card (initially 9200, now 9800 Pro) and I found the picture quality from the composite and s-video outputs very poor, so I started to look for alternatives.

Initially I made the cable as described on http://www.idiots.org.uk/vga_rgb_scart/. I bought a VGA cable, cut it, with a multimeter found all the cores I needed to use, and soldered on the scart plug. Usually these VGA cables don't have a pin '9' (+5v) (as used on http://ryoandr.free.fr/english.html), so I took the voltage from the PC's power supply. Not using the +12v, as I'm switching the TV to widescreen mode using the +5v. Also, since I'm not using my TV for sound I didn't connect up any audio.

When I started using this I found that I had a lot of interference on the other scart inputs on my TV, so had to look a bit further. Then found out that the composite sync that comes from the Radeon card is a TTL level signal (+5V). This would be fine for a monitor, but not for a TV! So, I had to find a circuit that would convert a composite TTL level sync to a format the TV is used to handling...

Found this:

You can forget about the first bit of the circuit, that's to go from separate horizontal and vertical sync signals to a composite sync (which we already have straight from the Radeon card). So, you would need the circuit from point '8' onwards. The shopping list would be:
- R3+R4: 1.8 kohm
- R5: 2.7 kohm
- R6+R7+R8: 47 ohm
- U1: 74LS86 or 74HCT86
- T1+T2: BC 547

Once I included that circuit my TV was a lot happier; no more interference. Using this VGA -> RGB scart approach you get the best possible picture quality from a 'modern' PC on an old-style television set. I am extremely happy with the end result:
- Much clearer picture, i.e. it's sharper but also the colours are much more vivid.
- Strict control over the screen resolution, no stretched faces etc. I'm using a custom 1024*576 resolution with the TV automatically switching to widescreen mode.

When playing with Powerstrip make sure you leave the ~5% overscan, that's how a CRT TV is supposed to work, makes the picture more 'stable'. This is not a problem in MP with the BlueTwo skin, as everything is based round the center of the screen, not the edges.

Word of warning: My 100Hz TV does quite a bit of digital processing, but I don't know how good it will be on a standard 50Hz set.

Enjoy the soldering!

2005-10-28, 11:15	#9 (permalink)
AberDino MP Donator Join Date: Feb 2005 Location: Kincardineshire Posts: 150 Thanks: 6 Thanked 1 Time in 1 Post Country: My System	The 'TV-Out' quality issue seems to come back every so often, and understandably so. I have a Philips 32PW9525 100Hz widescreen CRT television set, which is about 5 years old now. I'm using a dedicated HTPC with a Radeon card (initially 9200, now 9800 Pro) and I found the picture quality from the composite and s-video outputs very poor, so I started to look for alternatives. Initially I made the cable as described on http://www.idiots.org.uk/vga_rgb_scart/. I bought a VGA cable, cut it, with a multimeter found all the cores I needed to use, and soldered on the scart plug. Usually these VGA cables don't have a pin '9' (+5v) (as used on http://ryoandr.free.fr/english.html), so I took the voltage from the PC's power supply. Not using the +12v, as I'm switching the TV to widescreen mode using the +5v. Also, since I'm not using my TV for sound I didn't connect up any audio. When I started using this I found that I had a lot of interference on the other scart inputs on my TV, so had to look a bit further. Then found out that the composite sync that comes from the Radeon card is a TTL level signal (+5V). This would be fine for a monitor, but not for a TV! So, I had to find a circuit that would convert a composite TTL level sync to a format the TV is used to handling... Found this: You can forget about the first bit of the circuit, that's to go from separate horizontal and vertical sync signals to a composite sync (which we already have straight from the Radeon card). So, you would need the circuit from point '8' onwards. The shopping list would be: - R3+R4: 1.8 kohm - R5: 2.7 kohm - R6+R7+R8: 47 ohm - U1: 74LS86 or 74HCT86 - T1+T2: BC 547 Once I included that circuit my TV was a lot happier; no more interference. Using this VGA -> RGB scart approach you get the best possible picture quality from a 'modern' PC on an old-style television set. I am extremely happy with the end result: - Much clearer picture, i.e. it's sharper but also the colours are much more vivid. - Strict control over the screen resolution, no stretched faces etc. I'm using a custom 1024*576 resolution with the TV automatically switching to widescreen mode. When playing with Powerstrip make sure you leave the ~5% overscan, that's how a CRT TV is supposed to work, makes the picture more 'stable'. This is not a problem in MP with the BlueTwo skin, as everything is based round the center of the screen, not the edges. Word of warning: My 100Hz TV does quite a bit of digital processing, but I don't know how good it will be on a standard 50Hz set. Enjoy the soldering!