barney

Thanks all for the replies, and sorry for the delay in getting back to you with this progress update -- a couple of times I tried to log in and apparently the server was down. No idea what the cable from the camera is like inside, other than that it seems to have four conductors which are terminated with a four-pin DIN connector. The cable outer is perfectly round. I don't want to cut it open to look inside. I'd imagine that it's coax for the video signal or it wouldn't work too well, it would have to be an unusual kind of twisted pair to have 75 ohm impedance. Prompted by the replies here I looked at the printed circuit board of the old dead monitor and it does indeed have 75 ohm resistors terminating the video inputs. I dug out my aged oscilloscope and looked at the camera signal, and yes it drives 1V peak to peak into the DVR which also has a 75 ohm input impedance (at least according to the book it does). After messing about a bit more it seems my biggest problem was that the camera is very sensitive to poor quality power. I was running it from a lab-style power supply and when instead I ran it from a 12V lead-acid battery the image quality became very much better, to the point of being just about acceptable. So with that I'll thank you all very much for the shared brain power, wish you well, and hope not to have to trouble you more. Cheers, Barney.

Thanks for the replies guys. I understand that I could replace the existing camera but let's just say that operational considerations make that undesirable. Any suggestions to achieve my goal of using the old camera?

Hi all, my first post. Until recently I had a CCTV system consisting of a single monochrome CCD camera connected to a small all-in-one desktop monitor with about a 6" diagonal screen. The system is about 25 years old (I originally installed it). It has the name "Video King" on it. I believe that it was made in Korea. The model number on the camera is JHC-501C. The system has performed adequately for decades, but a few weeks ago the monitor died and it has resisted my attempts to revive it. The single cable from the camera to the monitor is terminated with a 4-pin miniature DIN connector which takes power from the monitor to the camera and signal from the camera to the monitor. I have no specifications for the power supply, nor for the signal. I bought a new DVR system (MicroLite K-DVR-4MLA). It has four inputs for video which are provided with BNC connectors. The supplier explained that it would be a simple matter to connect the old camera to the DVR but that appears not to be the case. Because the monitor for the old system had died and so could not supply power for the camera, I made a little breakout board to supply power to the camera from a bench-top power supply and to connect the signal from the camera to the DVR. The results were disappointing. An image was visible, but the quality was very poor compared with what was obtained on the old monitor. I suspect that this is because the DVR and the camera are working on different standards, but the power supply voltage for the camera could be an issue. As I do not know what power supply voltage I should be using for the camera, I limited the bench supply output to nine volts for testing. I imagine that twelve volts would be OK but I do not want to risk damage to the camera as it is installed in a building, and replacing it will be quite a task. I do not know what signal levels the camera provides, nor what the DVR expects. I do not know the characteristic impedances of the camera output and cable, nor of the DVR inputs. Can anyone point me in the right direction? Specifically does anyone recognize the model number of the camera and know what power supply voltage I should use? I have searched the Web but found only references to gaming machines. What voltage levels will the DVR expect? I'm guessing 1V peak-to-peak with 0.7V video and 0.3V sync but it's just a guess. Is there some converter/amplifier that will take all the pain out of this?