Not what I expected....... - UK Vintage Radio Repair and Restoration Discussion Forum

Brigham · 26th May 2006, 9:18 pm

Hello,
I bought a very tidy Bush TUG78 recently, a nicely restored example (There it no dust inside it!), chiefly because it came with a Ch.1 modulator, and a feature film on VHS.
I haven't managed to view the film yet. I get what looks like either extreme line pairing, or a 202-line raster, depending on how you look at it. The sound is fine, and the set behaves as you would expect otherwise, so I'm putting it down to my new VHS machine not being up to 405.
However, being naturally curious, I thought I'd see how a 405-line tape looked on a 625 system. And this was not what I expected!
The tape was played on a Panasonic DMR-ES30V, into my Sony DAV-S800 compact home cinema system, then out to an EIKI LC 7100 multimedia projector. And the film was watchable! The bottom third of the picture was filled with the stationary sort of 'white noise' associated with digital processing. The upper two-thirds was divided centrally by a vertical black bar, on each side of which two halves of a perfectly watchable picture were formed. The vertical bar proved to be the left and right sides of the 405-line picture, somehow slewed to the middle of the screen. A U-Boat passing from right to left on the film appeared from the left of the black bar, travelled off the left hand side of the screen, reappeared from the right hand side of the screen and disappeared again into the central bar. Similarly, characters facing each other conversing appeared to be back-to-back, speaking outwards. (Good job this wasn't a boxing picture!). The sound was exactly right, and so were the greyscales. Nobody had white hair and dark faces, which is what I was expecting.
I admit to being at a loss for an explanation. The frame pulse at line 202-and-a-half must come into it, but I haven't fathomed how. Has anyone else tried the experiment?

Kat Manton · 26th May 2006, 9:46 pm

Hi,

Your system's doing quite well managing to display a stable picture. 405-line composite video fed into the SCART on my nineties Misubishi displays an unlocked mess - well, I had field sync as both standards are 50Hz; but it didn't surprise me that the set refused to lock to the line sync (10.125kHz on 405-line against 15.625kHz on 625.) This situation arises fairly often as the same computer system is doing "double duty" as our main PVR system on the colour set in the living room as well as being used for 405-line; so I keep switching standards on it and sometimes forget what it was left set to.

The video signal would be the "right way up" anyway; it's only when modulated onto a VHF carrier to feed a 405-line set that it ends up the other way up (positive modulation) compared with 625 (negative modulation). All the basic levels (sync level, black level, white level) are the same on the two standards.

Regards, Kat

26th May 2006, 9:18 pm	#1
Brigham Octode Join Date: Mar 2006 Location: Co. Durham, UK. Posts: 1,118	Not what I expected....... Hello, I bought a very tidy Bush TUG78 recently, a nicely restored example (There it no dust inside it!), chiefly because it came with a Ch.1 modulator, and a feature film on VHS. I haven't managed to view the film yet. I get what looks like either extreme line pairing, or a 202-line raster, depending on how you look at it. The sound is fine, and the set behaves as you would expect otherwise, so I'm putting it down to my new VHS machine not being up to 405. However, being naturally curious, I thought I'd see how a 405-line tape looked on a 625 system. And this was not what I expected! The tape was played on a Panasonic DMR-ES30V, into my Sony DAV-S800 compact home cinema system, then out to an EIKI LC 7100 multimedia projector. And the film was watchable! The bottom third of the picture was filled with the stationary sort of 'white noise' associated with digital processing. The upper two-thirds was divided centrally by a vertical black bar, on each side of which two halves of a perfectly watchable picture were formed. The vertical bar proved to be the left and right sides of the 405-line picture, somehow slewed to the middle of the screen. A U-Boat passing from right to left on the film appeared from the left of the black bar, travelled off the left hand side of the screen, reappeared from the right hand side of the screen and disappeared again into the central bar. Similarly, characters facing each other conversing appeared to be back-to-back, speaking outwards. (Good job this wasn't a boxing picture!). The sound was exactly right, and so were the greyscales. Nobody had white hair and dark faces, which is what I was expecting. I admit to being at a loss for an explanation. The frame pulse at line 202-and-a-half must come into it, but I haven't fathomed how. Has anyone else tried the experiment?

26th May 2006, 9:46 pm	#2
Kat Manton Retired Dormant Member Join Date: Jul 2005 Location: West Yorkshire, UK. Posts: 1,700	Re: Not what I expected....... Hi, Your system's doing quite well managing to display a stable picture. 405-line composite video fed into the SCART on my nineties Misubishi displays an unlocked mess - well, I had field sync as both standards are 50Hz; but it didn't surprise me that the set refused to lock to the line sync (10.125kHz on 405-line against 15.625kHz on 625.) This situation arises fairly often as the same computer system is doing "double duty" as our main PVR system on the colour set in the living room as well as being used for 405-line; so I keep switching standards on it and sometimes forget what it was left set to. The video signal would be the "right way up" anyway; it's only when modulated onto a VHF carrier to feed a 405-line set that it ends up the other way up (positive modulation) compared with 625 (negative modulation). All the basic levels (sync level, black level, white level) are the same on the two standards. Regards, Kat