EX BBC PAL Coder

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g8kgh
Posts: 2
Joined: Tue Feb 16, 2021 9:55 am

EX BBC PAL Coder

Post by g8kgh » Tue Feb 16, 2021 10:02 am

I have just re-joined the club after an absence of many years and now I am starting to rebuild the parts I have lying around.
I have a pair of BBC white module coders ,both seem to work and produce PAL colour from RGB bars. However I am having problems in sorting out the relay switching for the RGB picture input. The backplane has been hacked about and extra wires added for some reason. Has anyone on here got diagrams of the coder? I have diagrams of each of the modules but nothing on how they interconnect on the backplane.

Malcolm

g8lce
Posts: 183
Joined: Sun Dec 06, 2015 10:26 am

Re: EX BBC PAL Coder

Post by g8lce » Mon Feb 22, 2021 9:39 am

The best idea may be to donate the coders to http://www.bbctv-lpu.co.uk/technical/ or another restoration team and use a Raspberry Pi for generating test signals. The equipement of that age was difficult to work on when still in use at the end of it's broadcasting life if it was used at Outside Broadcasts where I worked.

Martin G8LCE

g8kgh
Posts: 2
Joined: Tue Feb 16, 2021 9:55 am

Re: EX BBC PAL Coder

Post by g8kgh » Sat Feb 27, 2021 11:08 am

I have managed to get a complete set of diagrams and setup procedures. With these to hand I changed out all the electrolytics, most of which were showing signs of ageing, and then went through the set up procedure. At the end the coder was producing reasonable quality colour bars but several of the setup pots were at one extreme of their travel. I will now go through the modules again looking for out of spec resistors etc and see if I can bring it up to scratch.
Using a Pi wont work for me for various reasons. First I need to feed in CCIR RGB and get out PAL. Second, all my TV kit runs off an SPG so the coder must also be synced to the SPG so sources can be mixed or switched easily. Third, I enjoy repairing working with old technology, no software!

Malcolm G8KGH (EX G6ANZ/T)

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