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RGD 626 VC1

Pre War 240/405, Post War 405 Line, B&W Dual Standard, Colour Dual Standard, B&W S/S 625, Colour S/S 625 line, Hybrids. Standards converters & modulators, video recorders.
 
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RGD 626 VC1

Post by slidertogrid » Thu Aug 04, 2016 1:22 pm

I recently bought this set after it was offered on Paul's forum. I couldn't wait for it to arrive I was like a kid at Christmas!
I have very fond memories of the hand wired KB sets. I would buy them in the mid 70's from our local TV shop 25p each. usually missing valves and sometimes the speaker as well. the sets were stored outside so if it had been raining I would have to dry them out with Mum's hair drier.
Most sets didn't take a lot of getting going I think they were disposed of due to age more than a major fault. I suppose a lot of old stagers were coming in as their owners or renters turned to colour.
I had a quick look at the set today on the dining room table, I need to finish a radio chassis and clear the bench before it can go into the workshop.
The set shows a few previous repairs, mostly valves. there is even an old repair ticket still on the back.
it looks as if it started life as an unconverted set as the UHF tuner is a later transistorised one rather than the valve one that would have been current when the set was new.
the date on the smoother shows the set to be just two years younger than me!
I have given it a quick clean out inside and a wash and brush up on the outside. It really is in nice original condition. Better than some I had back then.
Next job is to get it on the bench and change the 'nasty' capacitors and reform the smoothers.
I will leave the Mullard Mustards but change the waxies and black Callun types on sight. I don't want to put any undue strain on the now elderly LOPT. I don't know if the oblong yellow capacitors are 'change on sight' or if they are lightly to be OK like the Mustards?
It should keep me busy for a while!
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Re: RGD 626 VC1

Post by The_Teleman » Thu Aug 04, 2016 1:33 pm

Nice set, we used to repair loads of these when I was an Aprentice back in the early
70's & by that time they where 10 years old or more but still gave great results
Looking forward to the restoration

Chris

 
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Re: RGD 626 VC1

Post by malcscott » Thu Aug 04, 2016 1:33 pm

A lucky find, very nice set. Looking forward to seeing the restoration, Malc.

 
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Re: RGD 626 VC1

Post by PYE625 » Thu Aug 04, 2016 9:38 pm

malcscott wrote:A lucky find, very nice set. Looking forward to seeing the restoration, Malc.


Ditto !!

As an aside, I often go to Suffolk for an annual holiday and always visit Framlingham.
It is a lovely little town and the castle provides some amazing views across the Suffolk countryside.

I wonder where "Framlingham Radio and Television Services" would have been in the town.
When I'm next there in September, I might ask a senior local if they remember :bba

 
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Re: RGD 626 VC1

Post by PYE625 » Thu Aug 04, 2016 9:42 pm

slidertogrid wrote: I don't know if the oblong yellow capacitors are 'change on sight' or if they are lightly to be OK like the Mustards?
It should keep me busy for a while!


I know the ones you mean, and should be ok like the mustard type.
But don't assume anything of course lol :qq1 :qq1

 
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Re: RGD 626 VC1

Post by Focus 2 » Fri Aug 05, 2016 6:25 am

Wow, I'm impressed. Amazing how the basic design remained in production for 7 years even ending up as the single standard VC100. In retrospect I'm surprised they didn't "upgrade" to a PL500/504 in later years.

Looking forward to hearing how you get on. The CRT looks to be a twin panel type.

Cheers
Brian

 
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Re: RGD 626 VC1

Post by AidanLunn » Sun Aug 07, 2016 1:28 am

So as this set is from Framlingham, or the surrounding area, for its VHF reception it would have received Manningtree and/or Tacolneston for BBC1 VHF, Mendlesham for Anglia TV VHF then Sudbury (which opened with BBC2 first in 1968 - which may account for the later transistorised tuner being fitted) for UHF services.

It might have even been able to receive Dover for Southern TV VHF then UHF, as Dover's coverage extends quite deep into Essex and Suffolk, whereas Crystal Palace (at least on UHF) usually couldn't get a good signal past Chelmsford and Southend.

 
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Re: RGD 626 VC1

Post by Till Eulenspiegel » Mon Aug 08, 2016 11:58 am

VC1 chassis identified by it employing an ECC81 as the line oscillator. If you experience weak frame hold there is a modification to solve that problem. The triode section of the PCL84 video amplifier is the white spot clipper, the valve socket is rewired to perform the task as frame sync pulse amplifier and clipper. It's a very effective modification. Check out the circuit of the VC2 to see how the modification can be done. I modified all the VC1 sets I had on rental. There is also a modification to remove the large thermistor which is in series with the mains input to the dropper resistor.

Till Eulenspiegel.

 
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Re: RGD 626 VC1

Post by slidertogrid » Tue Aug 16, 2016 8:18 pm

I had a chance to get the RGD on the bench finally. I replaced three capacitors that I found to be very leaky on a quick test around the chassis pre switch on. A Hunts electrolytic had corroded through one of it's leadout wires and was loose so I resuffed that with a new cap, I snipped the mains filter cap and put my AVO across the main smoother. Then with a hand on the switch I gave it some mains for a few seconds. The HT came up to around 100v before I switched off. I then cycled it on and off a few times allowing the HT to build up.
I noticed the HT decayed very fast when switching off so I suspected either had a short or the smoother was shot.
I left it on a little longer to allow the valves to warm up and just as a strained line whistle could be heard a resistor started to smoke badly.
After a check around I found the short was on the frame transformer, the fibre tag panel on to of the bobbin has curled up and enabled one of the tags to touch the frame of the transformer.
Clearing that short stopped the smoke and I found I could just see the raster collapse when I switched off. I then had a lingering spot which proved I had at least some EHT.
I had switched to 405 for switch on as I thought it might be Kinder to the lopt. I found though that only the 625 line hold pot adjusted the line speed.
On investigation I found the rocker is not moving the system switch I can't see why But I guess the linkage has broken or come apart.
Switching to 405 manually produced a lop sided blank raster the 405 line hold pot now working and far less scratchy than the 625 one!
Time to give it some signals! I connected the converter and selected channel 1.
I has clear sound and a very unstable picture but the tube looks very good!
Giving it some UHF and switching back to 625 produced a blank raster and distorted sound.
I then switched off and checked the lopt the secondary was barely warm but the primary was quite hot.
I decided that was enough for today I will let the lopt recover (hopefully) and then replace the rest of the capacitors in the line output stage before I run it again.
Then I will have a look to see what the picture fault is on 405. AGC fault?
Once it's working on 405 I will see what 625 does and then try and find out what is wrong with the system switch.
I am very please with progress so far though and the tube looks Ok which is a relief !
:bba
Rich
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Re: RGD 626 VC1

Post by PYE625 » Tue Aug 16, 2016 9:11 pm

Well done Rich, good progress and it looks like it will be a decent set indeed. :aad

 
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Re: RGD 626 VC1

Post by Cathovisor » Tue Aug 16, 2016 10:10 pm

Bottom picture looks like the sync separator has picture information on its output; check for a leaky cap going into the sync sep valve.

 
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Re: RGD 626 VC1

Post by Focus 2 » Wed Aug 17, 2016 12:36 am

Looks like the polarity is wrong, ie Negative going rather than positive needed for 405. This would of course upset the sync. The image reminds me of receiving a positive going French System L signal on a negative going UK 625-line set. You did mention problems with the system switch!

Excellent result so far, looking forward to hearing more.

Cheers
Brian

 
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Re: RGD 626 VC1

Post by Terrykc » Wed Aug 17, 2016 9:16 am

Negative vision can sometimes be caused by overloading - try reducing the RF input and see if the picture improves. If it does, it will confirm your AGC suspicions!

I did once have a fault (on a single standard VC100, but probably very similar) which was caused by a leaky coupling cap in the IF stages.

 
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Re: RGD 626 VC1

Post by slidertogrid » Wed Aug 17, 2016 10:52 am

I Tried reducing the signal input, on 405 anything less than almost full output results in a blank raster. If I reduce the contrast the picture does stop pulling a bit just before it fades out to grey. The contrast control seems to have slightly delayed operation which I think is normal on this chassis.
I will re check the system switch slider is intact and working on all sections but it is hard to see as the switch is an enclosed type on this set rather than the more usual open flat wafer type switch.
There are still a few blue and yellow tubular type plastic capacitors to suspect, the rest are Mullard 'Mustards' and yellow plastic oblong capacitors.
I need to dig out a circuit diagram next I think. Then I might have to go and borrow my scope back.
I am really enjoying this set. I have a few KB s in my collection. Both of my later sets with the VC53 chassis worked when switched on, no fun at all!
Hopefully I might get (be allowed) some time later today after errands are run.. :cch
Rich.

 
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Re: RGD 626 VC1

Post by marc » Wed Aug 17, 2016 11:38 am

Hi Rich,

Things seem to be progressing well with this RDG :aad
I have a KB XV05 on the 'tuit pile' which seems to be the same set as yours just with a little front trim difference so I'm taking notes of your restoration :qq1

Keep up the good work,
Marc.

 
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Re: RGD 626 VC1

Post by slidertogrid » Tue Aug 23, 2016 12:37 pm

Well I had a hour or so on it yesterday and got precisely nowhere! I noticed the brightness control wasn't working so I decided to find out what was wrong there first. the fault turned out to be a dry joint on a resistor which looked as if it had never been soldered from new. Having got that sorted I then started trying to sort the vision/sync fault. I worked my way around the video amp and sync separator checking capacitors, lifting one end and wiring a temporary replacement in place so as the original could be refitted if proved innocent.
I have checked the system switch is intact and switching correctly. It seems all OK, it has just disconnected from the actuating lever. Repairing that looks as if it will be fun! God forbid that it will have to be removed for repair. It makes a Roberts R707 wave change switch panel look simple!
The lopt primary is still getting hot after 20mins so fault finding time is a little restricted. I was just starting to think that maybe the fault is around the vision detector diode which is in an IF can when someone called round to see me so I decided that was excuse enough to call it a day. I don't want to start digging into IF cans before everything else has been eliminated.
I am going to pop and see my mate today and borrow my scope back, but annoyingly the VC1 manual doesn't have any waveform pictures..
The manual has various minor errors including a resistor shown as a capacitor number (i.e. R27 marked as c27) none of the signal diodes are marked on the chassis picture with a "D" number. they are just labelled 0A91 or whatever.
It looks as if some poor sod had the job of sticking loads of little ID labels on a photo of the chassis which was then re photographed. They must have got fed up by the time it got to the diodes! :cch
All the DC levels around the sync separator and video amp are pretty much correct. I have tried replacing IF, video amp and sync sep valves in case I had a h/c leak but no avail.
The lopt heating up is also a worry...
I will get back on it later today once I have my scope back, I am now realising how rusty I have become! It must be 20 years since I used a scope!
Any pointers as to what waveforms I should have around video amp and sync stages would be very welcome! At the moment I can only put the test card from the 405 converter on it as the set has no signals on UHF at the moment.
Rich.

 
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Re: RGD 626 VC1

Post by CTV » Tue Aug 23, 2016 1:26 pm

Beware the warm lopt. My 627 came without one, I found two spares it decided to eat them both one going up in flames. The third was OK. The lopt's in these seem very fragile but I may have just been unlucky with the first two unknowns. I loved the set so much I couldn't wait to see it gone. :qq1

Rich these waveforms should help from my VC.1 data manual. Also a sync fault guide.

vc1-1.jpg

vc1-5.jpg

vc1-2.jpg

vc1-3.jpg

vc1-4.jpg


The Vision detector diode GD12 was duff in mine, it was a very simple extraction.

vc1-6.jpg


Image
Image
Image

 
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Re: RGD 626 VC1

Post by slidertogrid » Tue Aug 23, 2016 5:28 pm

Many thanks Chris :thumb I will hopefully get back on it tomorrow It's very warm in the workshop at the moment ! I still need to get my scope back I didn't have time this afternoon in the end.
Can you remember if the diode was leaky or short in your set and what the symptoms were ? I'm clutching at strews at the moment with this set! Joking apart I am enjoying the challenge of it not being dead easy! I do have a spare unknown lopt I found but I don't know if its a VC1 or from a later set. I know the VC1 is different.
If the lopt is duff I might have to see if Mike will do a rewind for me I think he has done a couple of VC1 lopts in the past. At least the tube looks pretty good. I can't get that redone!
:cca
Rich.


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