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CTV ITT CK500 CVC5 Chassis

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Jayceebee
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I obtained this set about three years ago, I've not a lot of experience of the CVC5 but this is the hybrid CTV I've always wanted to own. The main smoothing block took a long time to reform but when tested both line and field stages suffered from the usual undulations caused by hum on the HT rails. Very little chance of finding a replacement but had a bit of luck, the PCB was drilled from the factory to accept smoothing blocks from different supplier. I was lucky enough to be able to fit a good quality cap for the reservoir and separate caps using the extra holes. Two links were required to connect the ground on a couple but it's fairly neat and tidy, I've kept the original in case I attempt a restuff at a later date. The set is not a great specimen so that may not happen, the chassis has a lot of rust and the cabinet needs a fair bit of damage repair and staining.

With the new caps installed a picture appeared but the CRT, particularly the green gun was a little lazy after it's slumber. After a short period all seemed to be going well and the CRT started to pickup when what we fear with all Philips made LOPTs happened. The picture began to foldover in the middle of the raster and quickly disappeared with the PL509 anode showing it's obvious discomfort. I was hoping it wasn't going to be a LOPT issue but various tests including disconnecting the tripler, checking the line drive and notorious blue/white 0.47uF boost capacitor all appeared fine. After a visit to @Crustytv Chris managed to fix me up with a used but rusty unit, it had been sat in a warm cupboard at home for well over a year so I thought it was about time I lugged the set on the bench and give it a try.

Before fitting the replacement a ring test was tried and although it was much better than the original which wouldn't give more than a couple of cycles the ring seemed to die a little quickly than I would have liked. Anyway after fitting the results were still the same, hot and bothered PL509, had I been wrong in my diagnosis? I went over the line osc/output stage with a fine toothcomb but couldn't pin point any other issues. At this point the set was shelved and a weather eye kept on eBay for a replacement.
Roll on several more months and after delivering some items to member @The_Teleman another Chris, I asked if he possibly had a spare stashed somewhere. He said he thought he just might have one and would let me know. A few days passed and a LOPT had been found, it was NOS and had "Rank T20" written on the overwind but Chris had correctly identified it a CVC5 type. After collecting I carried out a ring test which was pretty much similar to the first replacement, this had me again doubting my diagnosis.

The second replacement was fitted and the set powered, after about minutes warm up there was no more overheating of the PL509. I can't hear a 625 line whistle or even 405 now over my tinitus so a screwdriver was placed near the PL top cap. A small purple arc was obtained, next the tripler connection, a lovely big arc, success! Reconnecting the tripler brought up a blank raster with just a little hum on the audio which varied with the volume control, IF strip appears dead. Working on a CVC5 IF strip with it's double sided soldered edge connections is no fun, these were resoldered as they can often be intermittent but not today, more to follow.

IMG 0155
IMG 0157

John.

 
Posted : 25/02/2024 9:21 pm
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The_Teleman
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Well done John , I’m pleased that loptx worked 

just a quick point , check the 20volt supply on the left of the chassis , the AD161 and fuse and the small full wave rectifier just in front of the chroma delay line these all give the same symptoms of the I/f being faulty 

chris (The Teleman ) 

 
Posted : 25/02/2024 10:10 pm
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Jayceebee
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@the_teleman Hi and thanks Chris, I've checked the supply to the board and it's fine. I hope to have some more time with it tomorrow, I notice the IF board has Mullard lockfit transistors instead of those round ITT flat four legged devices and I'm wondering if someone has been there before me but it was working before the LOPT failed. Not sure if the transistors can be changed without removing the board, not a simple task.

John.

 
Posted : 25/02/2024 10:40 pm
slidertogrid
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Jayceebee It's decades since I worked on a CVC series chassis but I do remember removing an IF panel or two. Can't remember why or if I repaired the panel or just replaced it, ISTR if you get most of the solder off with a sucker and then mop the rest up with braid the panel will come out OK. So the panel does suffer but as to what goes wrong that information is long gone into my forgottonory.

One of my favourite sets ! CVC 5/8/9s were the last hybrids we had at the shop. Some going well into the eighties, outliving even the late Decca 30 varicaps which was another of my favourites.  

 
Posted : 26/02/2024 6:56 pm
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Jayceebee
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@slidertogrid Did use those plunger solder suckers but was never a fan, now I use only Chemtronics 10-25 wick. The best solder remover I ever used was the Denon SC7000Z and wish I still had one. Still available but eye wateringly expensive. The company bought them to desolder and replace sockets on early Videocrypt decoders on Pace satellite boxes which suffered intermittent issues due to metallurgy problems between socket and pins. It was never far from my bench.

Back to the CVC5, a couple of hours with it today the IF strip is dead. Not a sniff of anything from the sig gen getting through to the detector. On removing it which wasn't too bad a job the transistors, Mullard lockfits look to be original. I decided to remove and test all of them as it's not pluggable  and all three BFs read faulty which is a bit worrying. The main IF unit has two AGC controlled stages using BF196s, a single BF197 feeding the detectors and a BC172 for RF AGC. I could only find a single BF196 and no BF197 in my stores so I've ordered some. As a quick and dirty test I tried injecting video from a DVD player after the detector and did give something on screen, some unlocked inverted video and even traces of chroma so that was at least some positive outcome (forgive the pun) which bodes well.

CVCIF

John.

 
Posted : 26/02/2024 9:06 pm
slidertogrid
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Jayceebee Glad to hear you are making progress. It is true to say de-soldering equipment has moved on a bit since these sets were current. I still use a sucker and braid I'm ashamed to say! But to be honest it isn't often I need to use them.

Problems with Lockfits seem to follow a pattern, if one is faulty normally others in the same equipment also are either faulty or prone to fail and yet other equipment with lockfits doesn't suffer at all... This suggests to me it is either certain production or maybe down to storage conditions?

Anyway, I am following your thread with great interest! 

Rich

 
Posted : 26/02/2024 10:10 pm
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Jayceebee
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@slidertogrid No need to be ashamed, if it works for you then fine it's just I didn't get along with them. As for lockfits, only BF197s in the 1500 seemed to give any problems for me, maybe I've just been lucky. Seeing all three on the IF dead I was beginning to wonder if I had inadvertently put HT on the 20V LT rail but the test of feeding in external video and seeing some video albeit inverted and with vestiges chroma would suggest that was not the case, I hope.

Whilst looking closely at the board tonight I thought, where have I seen this before. Well I have a couple of the later ITT FT110 chassis sets, one working and one as a donor as it's missing the touch tune module and the convergence board has many pots with broken tracks. I've just had a look at the circuit and I've an idea it's pretty much the same board, electrically the circuit looks very similar indeed although the transistor types are 2 x BF198 and a BF199. I know I definitely have BF199s and will have a rummage for a couple of BF198s.

John.

 
Posted : 26/02/2024 10:45 pm
irob2345
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You can safely use BF199s in all signal positions in the IF, they will even replace the older metal can BF167 and BF173.

But even BF199s are getting hard to find. They want silly money for the earlier types.

 
Posted : 27/02/2024 8:55 am
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slidertogrid
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ISTR the VC200 Chassis used the same type of IF panel? Probably not the same electrically though.

 
Posted : 27/02/2024 9:59 am
Jayceebee
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Well, I'm getting there. I did manage to find a BF196 after all and a BF198 and all three were fitted into the IF strip. On power up I was rewarded with lot's of snow but when a signal was tuned it quickly looked like there was severe overloading. Leaving the aerial cable close to the socket I did manage to get an albeit weak locked signal with chroma but no audio but as soon the cable touched the socket then all lock was lost. Fitting an 18db attenuator helped but anything less and it was back to the same unlocked mess.

I got distracted with a side job for the OH and just left the set running with the attenuator for about 30 mins but I see things constantly improving. Saturation was weak but began to improve on it's own and the CRT's green gun emission picked up immensly. I set about looking for the audio fault and with careful tuning some vestiges of audio could be heard. The audio demodulator can is separte from the IF so I thought that would be the best place to start although it did have an additional stage driving it out of the can but not a lockfit. Sure enough in the can was a BF194 and this was also faulty, only had a BF194B in stock but it worked and restored good audio.

At this point I removed the attenuator from the aerial cable and although still overloaded no where near as bad. A slight tweak of the RF AGC pot settled everything down and the attenuator could now be removed. A quick setup of greyscale, beam limiter and convergence brought up a very presentable picture.
Still a couple of things to sort, vertical shift is one sidded and can move it up but down enough to be centered. The pot is part of the feed to the 20V LT supply pass transistor but plays no part in the adjustment of it, I was looking to see if there is a reversal plug but no.Also the chroma has now saturation to spare I don't think it looks right. Carole's red dress is tending towards orange and skin tones on other material look very slightly jaundiced. There's absolutely no issues with the grey scale other than the green gun being very slightly down on highlights. Checking the R-Y amplifier to the output stage shows voltages almost identical to the manual. Another thought is the type of CRT fitted, there's no manufacturer label on it but I wonder if it could be one of those imports that didn't have the rare earth red phosphors that we normally used to or am I being over critical here?

IMG 0154 (1)

John.

 
Posted : 28/02/2024 5:00 pm
Lloyd
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It looks pretty good from here! If the colours are off slightly, then it’s not showing in the photo, maybe a touch too much blue, but that is more than likely just the colour rendition on my phone screen. Certainly looks a good sharp picture!

 
Posted : 28/02/2024 9:34 pm
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Jayceebee
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@lloyd The greyscale is very good and the blue tint is actually my iPad camera, anything taken off screen with it tends to have a slight blue cast. The best ever camera I ever had for screen shots was an ancient Samsung Galaxy, long gone now unfortunately. Although the set has a tint control what I feel it needs in actually a tweak of an NTSC hue control to get it right. I'll have another look at the R-Y path tomorrow.

John.

 
Posted : 28/02/2024 10:06 pm
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Arc De Tripler
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Ooooh, the CVC5/CK500... the TV I cut my apprentice teeth on!

In the mid to late 70's, before my boss Tony started switching over our rentals to Ferguson, ITT/KB was our main bread and butter!

We loved these old hybrid TV's, they just seemed to go on forever... In fact, we were still servicing some of them right up until 2002 when we closed the shop down.

A few of our older customers just didn't want to part with them; we kept a large stock of parts, so repairs were still viable.

A story Tony used to tell us, sitting around the work bench, over a mug of strong coffee, was when the CK500 came out, they were like hens teeth and quite hard to get hold of in any useable numbers... but, the depot in Sidcup, already had a good stock of spare parts. Tony had been a KB dealer for years and knew the guys at the depot, so Tony, being the true entrepreneur, used to drive his old van over to Sidcup (it was like a trip out to the country in those days!) and buy the parts required, tubes, cabinets, chassis, etc... to build complete TV's!

These one's went on to be rentals - Identifiable to us years later, as having no model / serial number labels on the chassis!

I was going through an old box of bits at home a while ago, and there at the bottom, was the emerald green replacement (for the old blue and white) .47 cap!

Happy days! 

 

 

 
Posted : 29/02/2024 4:20 pm
irob2345
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That CRT looks like it could be an RCA, they had that distinctive Orange Red phosphor.

We used to see RCA 26" 90 degree Deltas in Oz production NEC (Rank Arena) and Panasonic (National) first release 26" sets, before Toshiba had their 26" 110 degree RIS in-line tubes in good supply.

They were bright, but those glowing orange reds looked awful!

I guess it didn't matter in Never Twice the Same Color land!

They also flashed over a lot and wore out quickly.

 
Posted : 01/03/2024 8:09 am
slidertogrid
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The CVC5 was sometimes fitted with a Toshiba tube which didn't have a very long life so could it possibly be have been fitted with a re-gun? Maybe with RCA Phosphor?  

 
Posted : 01/03/2024 5:47 pm
Jayceebee
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Unfortunately a relative with a GEC 2110 had a Toshiba 20" CRT fail after around 18 month old. I think I got the replacement from Philip H. Bearman and lasted the rest of the sets life.

I've not been able to do any further checks for the last few days due to distractions, plenty of saturation and no Hanover bars so other than some loss of gain in the R-Y feed I don't think it's anything to do with phase error in the reference oscillator. it's so long since I had any discrete PAL decoder faults other than no colour, or the PAL switch issue on my FT110. I have another two 20" CTVs so can try a swap to prove a point if needed.

John.

 
Posted : 01/03/2024 7:18 pm
irob2345
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The Toshiba CRTs we saw had very long lives IF you used the correct heater voltage.

6.0 volts RMS or DC.

6.4 volts and tube life was reduced to 25%

 
Posted : 01/03/2024 8:31 pm
slidertogrid
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Ah that's probably where the manufactures went wrong. I replaced a lot of 20" Delta gun Toshiba tubes that failed when the set concerned was still useful. ITT and GEC mainly. Later Toshiba PIL tubes lasted better, but they were mainly fitted to a Toshiba built set so maybe run as intended, within spec?  Overrunning would certainly explain premature failure, though to be fair Delta Toshiba tubes mainly were no worse than Mazda and probably better than Sylvania. I replaced a lot of those in Korting and Saba sets!   

 
Posted : 02/03/2024 8:24 am
irob2345
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We didn't see any Toshiba deltas here in Oz. The first Toshiba CRTs we saw were 110 degree large neck in-line.

When the self-converging tubes appeared they were also fast warmup. For these tubes the Pye T30C and T34 chassis used DC for the heaters, trace-rectified from the LOPT. The reason for this unusual approach (as explained to me by Russ Hauser) was to get more consistent 6.0 volts DC. Production shifts in the LOPT manufacture meant that the amplitude of the flyback pulse was not as accurately controlled.

My late mum had an early T30C (with Teletext!) and its CRT was still good after more than 30 years daily running. So I guess they got it right. That set ate triplers though!

 
Posted : 02/03/2024 9:18 pm
Jayceebee
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Just a quick update. It was an issue with R-Y, replacing T10 a BF197 made no difference. Checking various resistors around the transistor showed R86 in the emitter had increased from 220 to around 1K, surprising as it was a metal film type and probably not worked that hard. Replacing this has returned Carole's dress to the normal shade of red and a noticeable improvement in flesh tones.

Just the field stage with it's shift issue to sort now and it will be done. 

John.

 
Posted : 04/03/2024 10:32 pm
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