PeteWeedon
Technical User
Gracie and I bought a couple of second-hand monitors some time ago. They are Hitachi 19" models with five BNC connectors for the inputs. One of them came with a cable with 5 BNC plugs at one end and a three-row 15 pole D-type connector on the other. I think these units might have been used with a Sun workstation but I can't be sure of that.
We connected them to our 'dirty' computer which had an ATI Rage Pro graphics card fitted.
1) The monitors showed enough of a raster to suggest that all three channels (R, B & G) were working but, even with careful manipulation of the V-hold and H-hold controls, we couldn't get a locked raster. A bit of Web research led us to a site which mentioned that this model of monitor requires a 'constant-frequency' graphics card but I wasn't able to get any more technical explanation on that aspect. Please can anyone here enlighten me?
2) After this test, Gracie said that the graphics card had suffered some damage; when connected to an SVGA monitor, there is a complete screen but it has a thin horizontal line across the picture (sounds like one or more rows of video RAM have gone kaput?). I couldn't understand how this could be. In the old days of monochrome video, the video circuit impedance was 75 ohms and I'd assumed that each of the RB&G channels on an SVGA monitor would be of the same order. Surely the monitor can't send a damaging active signal back to the graphics card? With a cable such as I've described, the monitor ID pins in the 3-row D-type can't connect to any active circuit. If the Hitachi monitor has very low input impedances, it might blow one or more of the graphics card video line drivers but that'd show over the whole picture, not just a thin horizontal line. So, coincidental graphics card failure? If anyone can throw any light on this one too, I'll be grateful.
Best regards,
Pete W.
If you can keep your head when all about you are losing theirs - you haven't seen the latest Change Note!
We connected them to our 'dirty' computer which had an ATI Rage Pro graphics card fitted.
1) The monitors showed enough of a raster to suggest that all three channels (R, B & G) were working but, even with careful manipulation of the V-hold and H-hold controls, we couldn't get a locked raster. A bit of Web research led us to a site which mentioned that this model of monitor requires a 'constant-frequency' graphics card but I wasn't able to get any more technical explanation on that aspect. Please can anyone here enlighten me?
2) After this test, Gracie said that the graphics card had suffered some damage; when connected to an SVGA monitor, there is a complete screen but it has a thin horizontal line across the picture (sounds like one or more rows of video RAM have gone kaput?). I couldn't understand how this could be. In the old days of monochrome video, the video circuit impedance was 75 ohms and I'd assumed that each of the RB&G channels on an SVGA monitor would be of the same order. Surely the monitor can't send a damaging active signal back to the graphics card? With a cable such as I've described, the monitor ID pins in the 3-row D-type can't connect to any active circuit. If the Hitachi monitor has very low input impedances, it might blow one or more of the graphics card video line drivers but that'd show over the whole picture, not just a thin horizontal line. So, coincidental graphics card failure? If anyone can throw any light on this one too, I'll be grateful.
Best regards,
Pete W.
If you can keep your head when all about you are losing theirs - you haven't seen the latest Change Note!