Perplexed about multiplexing
Q: I am having problems playing back images from a VCR tape on a multiplexer. What do you suggest I do?
A: Firstly, as a member of the Technical Team at Dedicated Micros, I must say that this is a problem common to most, if not all, analogue multiplexers. Fortunately, it is also usually a very quick fix.
One of the first things to check is that the VCR and multiplexer have been connected together correctly. This can be confusing. The VCR output on any multiplexer should connect to the VCR input (Video In) of the VCR. Alternatively, the multiplexer’s VCR input should connect to the VCR output (Video Out) on the VCR.
You should then establish whether the multiplexer is a Simplex or Duplex model. If it is a Simplex, make sure it is in ‘record mode’ when you are recording to the VCR. Remember that Simplex models perform only one main function at any one time, whereas Duplex models can record whilst viewing a multiscreen or playing back recordings from a second VCR. If the multiplexer is a Duplex, then it should already be in record mode. Likewise if it’s a Triplex model.
When the machine is a Duplex there is a very easy procedure to check playback. Connect a short BNC to BNC Coaxial lead between the multiplexer’s VCR Input and VCR Output. Then put the machine into ‘Play’ or ‘Decode’ mode. If you see the pictures playing back then the multiplexer is certainly functioning correctly. Check that the wiring to the VCR is correct and examine the Coaxial leads for breaks.
If you’re working with a Simplex multiplexer, connect a BNC to BNC coaxial lead from the machine’s VCR output direct to a monitor in order to check the video signal.
Still not working?
If all is still not well, make sure that the multiplexer has been configured correctly for the VCR model and timelapse mode. It is crucial that the VCR timelapse mode and the multiplexer are synchronised exactly. This is because the multiplexer has to send the fields of video to the VCR at the same rate as it can record them, therefore if they’re not matched exactly, you will have irregular update rates, missing frames of video, or no playback at all.
Finally, in order to check if the VCR has recorded the images, connect the Video Output of the VCR directly to a monitor and press ‘Play’.
Where can I get answers?
Q: I am new to CCTV installation. Is it possible to to get back issues of your Can We Help comments in Security Installer?
A: Yes. The Dedicated Micros website includes a ‘Can we help?’ section which reprints readers questions and our answers. The archive dates back to 1998 and covers a wide range of problems encountered by readers and the advice given. Many of these are common problems that have a wide interest. Visit www.dedicatedmicros.com. Click on the “On-line Technical Support” option and then the “Other Information” box where “Security Installer” will be found.
