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CTV 1982 Rediffusion Mk4

 
WayneD
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I'm now the proud new owner of Chris Crustytv's 1982 Rediffusion Mk4! 

The Rediffusion Mk4 has a particular interest to me as when I was a teenager back in 1993 I found one abandoned in someone's garden. I took it home, cleaned out the leaves, fixed the cracked board, soldered the yoke back together and then sold it for £75 to someone with a Nissan 200SX who then proceeded to lie it face down into the boot of the car... 😮 Another interest more recently is one being used in the Channel 4 series Toast of London, where the main character Steven Toast (Matt Berry) watches the funeral of Winston Churchill on one. 

Screenshot 20211227 130336 Messenger

I know Chris had done a bit of work on it to get it going including the replacement of a thyristor, so I couldn't wait to play with it when I got it home. It powered up no problem, however I had a bit of difficulty getting it to tune into my RF modulator. I know Chris had mentioned in his blog about this being originally set for wired operation rather than UHF operation but I couldn't be 100% sure if my RF modulator wasn't at fault here either so I thought I'd try the composite video input. However, I noticed the snowy picture wouldn't disappear when I operated the switch and also the LED remained unlit. Time to get the back off:

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Oh man, this takes me back! Whilst I've repaired a few smaller sets on the bench there's nothing like taking the back off a TV on the floor of a living room. 

The DPDT switch to change between RF and composite video input mode has failed, it has zero continuity in the composite video mode:

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I have spares somewhere but for now I'll just bypass it. That's looks more promising:

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Hooking up my modded Playstation 3 to it and try some YouTube videos before watching the Kenny Everett DVD my wife bought me for Christmas:

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Looking good! I've noticed the sound is fairly quiet and distorted but according to the Television article from January 1994 it's most likely capacitor 0C33. There's a couple of other small issues like the black level not being consistent across the whole screen but again I think that's tired capacitors. Considering this thing is nearly 40 years old, it's forgivable! I'll be spending a lot of time going through this TV as the cabinet is in such good condition it's well worth keeping it going for as long as possible. 

Oh yeah, that scene from Toast of London being played on the TV:

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Topic starter Posted : 27/12/2021 9:43 pm
Lloyd liked
crustytv
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Hi Wayne,

So glad the Rediffusion has found a good home where it will get plenty of love, care, and use. As I mentioned in our messages earlier today, the TV was only ever tested on UHF, and it gave a fantastic picture once I sussed the tuner settings. It was then never switched on again. Unless something has given up since on the IF side or come loose in transit, I would suspect your modulator.

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Posted : 27/12/2021 10:03 pm
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WayneD
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@crustytv Yeah, normally I use my Amiga computer for testing RF as it's got a good stable output but it's in a box stashed away at the moment. Interestingly enough, the Kenny Everett DVD looks terrible on our 2018 Samsung LCD as it's not been cleaned up at all, Captain Kremmen in particular looks really grainy. Yet it looks really good on the Rediffusion. For a while it's been known that old video games look better on CRT TVs but I think this something else that needs addressing. 

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Topic starter Posted : 27/12/2021 10:23 pm
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lyons.den@ntlworld.com
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Brought a Brand New 22 inch Mark 4 back in July 1984 but was disappointed  with the quality of the Picture compared with our earlier Mark 3. The main problem was adjusting the Brightness and Contrast settings to an acceptable level. This was apparent eg. watching a Football Match where part of the pitch may be in Shadow caused by the stands due to time of day/direction of the Sun etc. That part of the screen would be in total darkness and adjusting the Brightness an Contrast settings revealing the blacked out area of the picture meant that the rest of the picture was too bright to watch . Numerous visits by the Engineers and soak testing back at the workshop made little or no difference to the quality of the Picture. Ended up selling it 4 Years later and replacing it with an excellent Sony Black Trinitron which gave good service for 20 Years.        

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Posted : 29/12/2021 4:19 pm
malcscott
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The Mk3 always beat the Mk4 for picture and sound quality in my opinion. I still have a dozen or so Mk1/Mk3/Mk4 sets in my collection. All in good working order. I have an early Mk3 prototype 20 inch sent from the St Helens, Bishop Auckland factory to our w/shop at Newton Aycliffe in early 1976. Never had a crt failure with the 20 inch Mk3. Used Hitachi crt, later Finvalvo crt (Hitachi) Malc.

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Posted : 29/12/2021 4:38 pm
WayneD
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@lyons-denntlworld-com I haven't noticed anything that bad with this despite it needing work. That said my eyesight isn't what it was. It does have a very nice picture but I already know some capacitors are failing.

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Topic starter Posted : 29/12/2021 6:25 pm
Lloyd
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Nice to see another MK4 getting some attention! There’s a 22” with Teletext hiding in a dark corner of my workshop, it’s not seen the light of day for a couple of years.. there’s a thread about it here.

Regards,

Lloyd

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Posted : 29/12/2021 6:25 pm
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WayneD
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@malcscott I seem to recall the Mk3 seemed to commonly have two speakers, a large one in the usual place and a smaller one above the channel selector. In fact the only single speaker Mk3 I think I've seen is the one that gets destroyed in Father Ted!

The sound is really bad on this Mk4 so it's certainly the first thing I'll address.

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Topic starter Posted : 29/12/2021 6:26 pm
malcscott
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Try adjusting the 6mhz intercarrier coil for sound prob. The only single speaker mk3 were the cable conversion sets.

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Posted : 29/12/2021 6:33 pm
WayneD
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@lloyd I'm intrigued as how the teletext board connected to the video board. I'm guessing it just went to the OSD pins of the TDA3303 but did it have a connector or anything?

I recommend Teefax by the way, if you're looking to get a teletext feed into it.

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Topic starter Posted : 29/12/2021 6:33 pm
WayneD
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Posted by: @malcscott

Try adjusting the 6mhz intercarrier coil for sound prob. The only single speaker mk3 were the cable conversion sets.

It's doing it with the sound when using a composite video input too, hence why I think it's an amplifier problem.

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Topic starter Posted : 29/12/2021 6:48 pm
malcscott
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@wayned Sorry, didnt realise. Got a few i/f panels here (untested) if you need one.

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Posted : 29/12/2021 7:07 pm
WayneD
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@malcscott cheers for the offer. I'm going to give everything a good going over, probably check/replace capacitors as required. 

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Topic starter Posted : 29/12/2021 10:43 pm
malcscott
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@wayned Check A/V input pcb for damage.

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Posted : 29/12/2021 10:46 pm
WayneD
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It was one leaky capacitor, the very one that was mentioned in the January 1994 issue of Television magazine. All working now! Just need to replace that faulty switch. Even the uneven black levels across the screen seem to have disappeared with use. 

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Topic starter Posted : 01/01/2022 3:57 pm
malcscott
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Have you checked the usual dry joints around psu chopper t/x, snubber cap? Show a pic of on/off switch. could have nos ones.

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Posted : 01/01/2022 4:39 pm