Hello guys,
Not sure if I'm posting in the right place but here it goes.
I was asked to go and look for a problem in a CCTV system using an old Visilynx equipment. I made a sketch showing how all the equipment is connected (I have ignored video signals, I'm only showing control):
Basically there are 16 cameras that are connected to the Visilynx System (Rack 1 and 2) through optical fibre using Fiber Options Transmitors/Receivers (731-R/T and 735-R/T). Details of the Optical Interfaces can be found if you google "GE_Manual_S731DV" and "GE_Manual_S731DV".
Everything works fine except Cameras 14 and 15 (both JVC TK-C655) suddenly lost the control but NOT the picture. You can see that the data link from all the other cameras that work fine (Cam 1 to 13 and 16) is connected to a PLW314 card on the Visilynx system. This card is used for camera control (up to 32 cameras per card) RS485 (2 wire).
On the other hand, the control signal from the other 2 cameras (CAM 14 and 15) is connected to a PLW 309 card. According to the manual, this card is used for PC control and other devices equipped with RS232 interfaces. I couldn't understand why this card has been used to control those cameras but the fact is that it did work before. There was a spare PLW309 card so I decided to swap the cards and then I realized the following:
This is a normal PLW309 board:
And this is the card that I found connected to control cameras 14 and 15:
You can see that the original MAX232 chips at the top were replaced by a circuit with a MAX485 chip.
Any ideas of how to troubleshoot this problem? Is there a way of measuring or testing RS485 data coming from the card to the cameras? I'm convinced the problem is not with the cameras or the Optical link/Interfaces because we are getting a video signal. Problem as to be with the Visilynx system, I suppose.
Also, I know that a RS485 link has to be terminated at the ends. My question is if you have a optical link in the middle, how do you perform the termination (the optical interfaces have options to terminate an RS485 link)?
Thx for reading. Bye,
Jorge
