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Trade Chat PYE FET Lynx TV camera

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Lloyd
(@lloyd)
Posts: 1958
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Whilst messing with the workshop RF system last weekend I had to move a few bits to get to the wiring, one of them was this old camera, can’t remember when I got it, but I do remember it working. So I fired it up and connected it to a TV, and got nothing! The tv was one of those modern ones that just has a blue screen with no signal. Then I connected it to a small LCD monitor, on that you could get a light band bobbing about on the screen, and with some settings of the controls you could see it reacting to light.

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I pulled it apart and did some voltage checks, there should be 200V+ going to the tube, but I couldn’t find anything above 60V… found a couple of dead 2uF electrolytic caps, and changed them, this got some better voltages, but still no picture.

I found a decent copy of the manual on Electrotanya, and got the scope out to have a look at what was happening. When I got to the horizontal section everything seemed dead! The oscillator was not oscillating at all, and a few checks later I discovered the horizontal speed coil was completely open circuit 🙁

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so I guess what I was seeing on the monitor was the result of a single vertical line spread across the screen! The coil is toast, and it’s a wave wound thing, no chance of repairing it! I couldn’t even get a reading with the Megger on its 1KV range… 

So for entertainment I dug out the function generator and injected a 15.625kHz sine wave into the place where the dead coil came from, an after a few tweaks of the controls I had a picture!

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It was very unstable, and there are some serious burn marks on the tube, but it does seem to work! I could even wind the function generator down to 405 lines without changing any components in the camera..

So a new coil is what’s needed, or a substitute. No idea what made it go open, there is hardly any current flowing through it, I couldn’t pick up any voltage on it either, and the camera hasn’t been damp, it’s not as if it’s very fine wire either, it’s quite robust feeling! Once the function generator was doing its thing all the waveforms that should have been there were present, and actually looked sensible.

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Regards,

 Lloyd 

 
Posted : 09/04/2023 11:18 am
Lloyd
(@lloyd)
Posts: 1958
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Topic starter
 

Done some more bodgery, I found some inductors and thought I’d try them in the Lynx, most of them would get the oscillator going, but all at supersonic speeds… the closest came in at 38kHz, so I pulled the wire off it and rewound it with thinner wire, no idea how many turns, but got the oscillator running a bit slower, 21kHz. I found that I could bring it down further with a capacitor strapped across it, I used a 10nf cap, which brought the speed down too much, 14.300kHz, then sticking a small magnet to the top of the inductor and rotating it I could bring the speed in almost perfect!

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Maybe I’ll pull the original coil apart and see if it still works after rewinding, but it won’t be wave wound if I do it… 

Regards,

 Lloyd 

 
Posted : 09/04/2023 8:55 pm
Doz and FRANK.C reacted
Doz
 Doz
(@doz)
Posts: 1535
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Well done. Necessity is the mother of invention. 

 
Posted : 11/04/2023 3:44 pm
Lloyd reacted
Lloyd
(@lloyd)
Posts: 1958
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Topic starter
 

Cheers 🙂

 I’ll hopefully be able to fix it properly one day! Needs a load of new caps as well, most of the electrolytics are a bit sick, and some of the Wima caps are split too. The picture jiggles up and down and it sometimes loses horizontal sync for just a second.

I also have a Panasonic WV-71, it’s a Vidicon camera that was supposed to be used with a specific monitor, the WV-72, which I don’t have. Power and signals are all on one cable, and applying power to the BNC makes it come to life, you can hear the horizontal timebase running, but I read somewhere that the vertical gets a signal from the monitor to make it run. I won’t be bothering with that camera as the tube has air in it! It glows a lovely blue colour when it’s on, and looking at the tube, the getter has started going white round the edge. The heater still lights though! I did see another tube on eBay, but it was expensive, and also had a white getter!! 

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Regards,

Lloyd

 
Posted : 11/04/2023 4:39 pm
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