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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 12th Dec 2006, 10:05 pm   #1
Kat Manton
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Default Recycling VCR Modulators

Hi,

A while ago I started a thread, Non-UK Modulators Wanted. Well, yesterday, thanks to Andrew ('arjoll'), a few arrived all the way from NZ (in record time.) Thanks, Andrew.

I've started off with the two VHF ones, both identical types. One came from a Sharp machine and the other from an Akai. They're made by JALCO but information about them seems scarce, I couldn't track down a datasheet. Probably they're old enough to be obsolete by now, hence no data on the manufacturer's site.

I already knew these were System B, hence would be useful for feeding 625-line signal to the multistandard 23" Sondyna TV I've almost finished working on.

So, a little detective work was called for. They use the Sony CXA1122P RF modulator IC, www.alldatasheet.com has a datasheet for the CXA1122AP. Near enough...

It didn't exactly take long to work out the connections, there's not a lot inside the little can. There's the modulator IC itself along with what I guess is an RF preamplifier between the aerial input and output. Power is supplied seperately to the modulator and the RF circuitry. In the original application, the RF circuitry would be permanently powered with the modulator only being powered when the VCR was switched on.

Time for a quick lash-up... I dug out an old Rediffusion Frequency Translator (aka Display Electronics "Telebox") and hacked something together. 12V was available, the modulator IC spec. calls for 4.4V to 9.3V at around 20mA. So, I glued a quick and dirty supply together comprising a 180R series resistor and 5.6V Zener diode shunt regulator then gaffer-taped the thing onto the back.

Then I hooked up the UHF aerial input to the distribution amplifier and connected the RF output of the modulator to the VHF aerial input of the Sondyna TV. With much twiddling of tuning controls, at last, for the first time since I got the set, it was fed with one standard it was designed for.

The picture was somewhat nasty, the video signal fed into the modulator being too high. The "quick fix" was to add a 100R preset across the video output, wiper connected to the modulator's video input, then twiddle the preset while watching.

It's all a bit "bodgetastic" but it means I've finally been able to prove that I've fixed the sound fault on the Sondyna. Sound and pictures are both rather good.

Now I know it works, the plan is to fit this modulator along with others for various standards in nice matching boxes. With the FotH System, a few homebrew projects (for System A and E) and further scrounging of bits of dead VCR, I should be able to feed any TV set from anywhere with an appropriate signal...

Cheers, Kat
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Old 13th Dec 2006, 1:36 am   #2
ben
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Default Re: Recycling VCR Modulators

I have a couple of System G ( PAL G, UHF ch. 32-39 variable O/P) modulators; if they're any use to you send me a PM.
cheers
Ben
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