UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - FothTV (405-line from a PC)

Kat Manton · 25th Aug 2006, 6:14 pm

Hi,

I've been pondering the complexity of the MkII RGB combiner, trying to come up with something simpler and consequently easier and quicker to lash up.

This is the end result, it uses the smallest number of parts I think it's possible to get away with while still "working".

This just crudely adds composite sync to the green video signal, ignoring red and blue. I've tried it with monochrome and colour DVDs and it works pretty well, considering. Field-sync is just one broad pulse which my fussy Pye monitor doesn't like, I get line-pairing as happens with the XORed syncs from the "MkII". But I do get a locked 405-line picture. Well, sort of...

I'm not sure what a VHF modulator will make of it, though; I've still not built one.

But, here it is - it could be worth trying this first, then work up to better circuits later

Code:

         | | 47uF
GREEN ___| |_________________________
         | |                         |
       - | | +                       |
                             680R    |
HSYNC ___________       ___/\  /\  __O___ GREEN + CSYNC
                 \    _/     \/  \/
                  \   /|
                  =====  
                    | 2N3904
           1k0      |
VSYNC ___/\  /\  ___|
           \/  \/

(I'm not claiming originality; I found a few circuits for feeding "Sync on Green" monitors while trawling the 'net for ideas, this is a rip-off of one of them...)

So... you need this, a suitable PC and a modulator...

I should add that this requires both syncs to be negative-going, so you need "-hsync -vsync" in the modeline.

Regards, Kat

25th Aug 2006, 6:14 pm	#1
Kat Manton Retired Dormant Member Join Date: Jul 2005 Location: West Yorkshire, UK. Posts: 1,700	FothTV (405-line from a PC) - KISS Circuit Hi, I've been pondering the complexity of the MkII RGB combiner, trying to come up with something simpler and consequently easier and quicker to lash up. This is the end result, it uses the smallest number of parts I think it's possible to get away with while still "working". This just crudely adds composite sync to the green video signal, ignoring red and blue. I've tried it with monochrome and colour DVDs and it works pretty well, considering. Field-sync is just one broad pulse which my fussy Pye monitor doesn't like, I get line-pairing as happens with the XORed syncs from the "MkII". But I do get a locked 405-line picture. Well, sort of... I'm not sure what a VHF modulator will make of it, though; I've still not built one. But, here it is - it could be worth trying this first, then work up to better circuits later Code: \| \| 47uF GREEN ___\| \|_________________________ \| \| \| - \| \| + \| 680R \| HSYNC ___________ ___/\ /\ __O___ GREEN + CSYNC \ _/ \/ \/ \ /\| ===== \| 2N3904 1k0 \| VSYNC ___/\ /\ ___\| \/ \/ (I'm not claiming originality; I found a few circuits for feeding "Sync on Green" monitors while trawling the 'net for ideas, this is a rip-off of one of them...) So... you need this, a suitable PC and a modulator... I should add that this requires both syncs to be negative-going, so you need "-hsync -vsync" in the modeline. Regards, Kat Last edited by Kat Manton; 25th Aug 2006 at 6:23 pm. Reason: Added note about modeline