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Another Keracolor!

 
slidertogrid
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Hi all, well I have gone and done it now! I have bought myself a "Marmite" set!
Love it or hate it the Keracolor was without doubt a Icon of the 1970's colour boom. Favoured by the 1970's nouveau riche, used car lot owners and trendy Londoners.
I remember an episode of "The Good life" that had one in a trendy apartment that Tom and Barbara had borrowed for the weekend. (while Margo and Gerry looked after Tom's home made generator...what could possibly go wrong?)
I also have some not so fond memories of a few struggles I had with one that belonged to a local used car lot owner. The set was used heavily as the family's main set, he was the first person I saw with a Video recorder so the kids and "Er indoors" had the set on all day every day.
The panels got quite cooked over the years and I can remember many a RGB fault and quite a lot of crispy pots on the convergence panel.
I have keeping an eye out for one but not too seriously. I always found a reason not to bid, I wanted an untouched set. I don't mind and quite expect there to be some knocks and marks but many I saw had been sprayed or worse had been gutted and another chassis fitted.
Finally the other day I saw one for sale that had it's original Decca 30 chassis, was within a reasonable distance and the best bit...It was a reasonable price.
After a struggle and a lot of help from a mate with a van I got the set home. It is very heavy and only just went through the patio door!
My first job will be to make it a bit more presentable. At the moment it is quite dirty and has lots of black marks on the trumpet of the stand. The stand will need some repairs as there are a lot of small cracks around the lip of the base, it is also quite wobbly so will probably need a bit of re-enforcing inside the "trumpet".
A look inside shows the set has lived in a smokers house but it's not too bad. The lopt looks like a replacement and it has an ITT tube fitted. I always thought Decca used Mullard tubes so maybe this is a replacement?
Once I have given it a clean I will try some power and see what happens, I was told by the seller that it hadn't been powered for years but the boost capacitor looks suspiciously new...
:thumb
Rich

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Topic starter Posted : 02/06/2015 7:55 pm
Doz
 Doz
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Must be later than mine, mine has a Bradford 10 chassis. What tube is fitted? Mine has a mullard A63-11X fitted, although quite how it survived, as when I picked the set up, it was in bits with the tube in a cardboard box, lent on it's neck with most of the pins bent!

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Posted : 02/06/2015 11:15 pm
slidertogrid
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Hi mine is fitted with a A66 120x. Is yours one of the fiberglass ones ? I read up on the history of the development of Keracolour and the first few were apparently made in the designer's garage and supplied to Harrods. I didn't realise they used the 25" tube though. They must have had to change the moulds for the later squarer tube. Mine is one of the later plastic cabinets.
Does yours have a seam in the cabinet or is it one piece excepting the back?
I have spent some time cleaning and polishing the set, most of the black scuff marks have polished out, it is looking a lot better already.
Tomorrow I am going to try some power and see what smokes...
Rich.

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Topic starter Posted : 03/06/2015 2:56 am
Doz
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Mine's fibreglass, and the sphere is one piece. The base and back are separate and fibreglass.

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Posted : 03/06/2015 1:56 pm
Doz
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The thread is here http://www.forum.radios-tv.co.uk/viewtopic.php?f=5&t=7172&hilit=keracolor

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Posted : 03/06/2015 1:59 pm
slidertogrid
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Hi yes that's a lovely set ! The fibreglass ones don't have the seam that the later plastic ones have, according to the Keracolor website the sets were moulded by a few different firms over the years and the introduction of the seam caused some complaints from the dealers.
I suppose the catalogue showed a set without the seam and customers preferred the "cleaner" shape...
I introduced the set to some mains today, I brought it up slowly and the results are encouraging, At first I had a bright green screen, that was the 10K wirewound resistor in the green output open circuit. It didn't take a lot of finding, it was loose on it's legs. (some days I know how it feels.. :) ).
The tuner won't tune, I will come back to that, for now I have taken the spring off the cast bar and tuned a pattern generator in manually.
The tube emission is very good. The convergence is terrible and the colour difficult with a reversed phase down the right hand side of the screen. This is when the colour decides to put in an appearance, it's shy most of the time!
So a few jobs to do, it is over 30 years since I did battle with a Decca 30 so I am off to see my mate Mick this afternoon to borrow a circuit.
I will post some pics later if I can work out why the camera won't connect to my laptop! :ccg
Rich.

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Topic starter Posted : 03/06/2015 4:25 pm
Rally coordinator
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The best of both worlds - a classic Keracolour set with the added advantage of being to work on a Decca 30 chassis!!

This is when the colour decides to put in an appearance, it's shy most of the time!

Wasn't the main suspect with the majority of Decca 30 colour decoder faults (although possibly not in your case) found to be a faulty MC1327P IC?

Mike

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Posted : 03/06/2015 6:30 pm
slidertogrid
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I now hopefully have some pictures of the set. the last pic is of the splits in the rim of the stand. I will worry about that later once I have it running properly. I'm not sure about the decoder chip I can recall changing one or two but as to what the problem was.. that memory has long gone!
:thumb
Rich.

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Topic starter Posted : 03/06/2015 7:05 pm
slidertogrid
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I had a couple of spare hours today and having borrowed a circuit I thought I would have a quick look at the decoder. I know the sensible approach would be to sort the tuner first but that means removing the front panel. I am going to put that off until I repair the top right hand tube mounting which has pulled through the plastic. This means the chassis and tube will have to come out eventually so I might as well only have the front panel out once..
Overriding the colour killer didn't make any difference. I have checked the voltages around the chip and they are all correct.
The colour is prone to flick on and off at a certain tuning point and seems to sort of pull in from the left hand side of the screen and then wash over the picture for a second or two and then go. Moving the tuning slightly repeats the effect.
I am wondering if the reference pulse from the line stage is weak or distorted it may be time to dust off the scope.
I see there are a few lockfit transistors in the decoder and knowing their reputation I may have a fight on my hands...
Any Decca decoder experts out there? :ccg
Rich.

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Topic starter Posted : 04/06/2015 8:19 pm
Terry
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The tuning sensitivity might point to an IF problem. Put a 'scope on the detector and check what happens to the chroma content in the fault/no fault situations.

Alternatively, if it has a SCART socket, try feeding it with a composite video signal from a VCR, DVD player or Set Top Box.

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Posted : 04/06/2015 9:33 pm
slidertogrid
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Some more progress, after a bit of chasing around the decoder with the scope I narrowed it down to the "pulse shaper" stage. I pounced on the BC147, ah ha! very leaky! Replacing it restored much better colour lock but now the picture was dark and it still had the reversal on the left of the picture. The pulse on the base of the transistor was small and wrong. I found R218 had gone very high. replacing that cured the phase error and restored the brightness to normal. So it looks as if the leak in the transistor somehow masked the fault caused by the resistor?
The colour is slightly noisy on the verticals, but I have had enough decoders for today!
The next job is to get the convergence better, that or buy some 3D glasses!
Rich.

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Topic starter Posted : 04/06/2015 11:38 pm
slidertogrid
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An hour setting the convergence and a slight tweak to the delay line balance and the Keracolour is now showing a very acceptable picture. It's not perfect but at normal viewing distance it will do for now.
Next job will be to remove the panels one at a time to give them a clean and check over for dry joints and to evict any suspect capacitors before they have chance to cause any trouble.
:thumb
Rich.

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Topic starter Posted : 19/06/2015 11:58 pm
Doz
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Looks great Rich :aad

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Posted : 20/06/2015 1:36 am
slidertogrid
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Some improvement to the frame linearity will be my next job. The linearity drifts as the set warms up, the top expands slightly and the bottom compresses. Adjustment is made difficult as the height pot is very scratchy and has so far not responded to switch cleaner.
I am hoping renewing a few capacitors and maybe the pots on the frame panel will sort things out. Most of the valves are replacements and seem Ok but I do have one or two spares if needed.
The last job which I will put off for as long as possible will be to strip the set out clean the inside of the cabinet and repair one of the top CRT mountings which has pulled through the plastic, repair the stand and the cracks in the rim. plus sort out the tuner and front panel mountings.
Someone has secured the top of the front panel with a self tapping screw through the front above the top tuner button. I want to make a tidier job than that, either doing away with the screw completely and filling the hole or possibly replacing it with a domed white nylon plug which would look neater.
To be honest the Keracolour was a little bit of a spur of the moment purchase and when I saw how big it was a wondered if I had done the right thing :ccf but I am pleased I did buy it now. I really enjoy working on a Decca 30 chassis again after all these years! It reminds me of when going to work was fun... :aal And profitable..... :bba
Rich.

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Topic starter Posted : 21/06/2015 5:03 pm
mark pirate
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It certainly was a worthwhile restoration, I think it is a great looking set ttt:
The good old Decca 30 chassis was one of the best of it's time, you were very lucky to find an original set that had not suffered a nasty chassis transplant.

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Posted : 22/06/2015 9:30 am