CTV [Sticky] 1977 Rank Arena AC6333 - T12A Chassis - Teletext

With only 40 volts on the collector I would expect the collector load resistor to be getting red hot, that is unless your load resistor is open circuit and the 40 volts is comming from the CRT s cathode itself. 

Nope, R70 was the first thing I checked it reads 9.8K in circuit, the same as the other two.

With the contrast and brightness to max (if you don't set them this way, you just see green and retrace lines)  and with the A1s compensated, the test card is stable and visible. The video shows the visible retrace lines and this odd bar scrolling down the screen, and the overall green tint.

Edit:

One positive among all this, the restored ultrasonic remote works with the set perfectly 😎 

I’m assuming the decoder is similar to the 718 series 

if so ic3 being a TCA800 check by replacing those 3 capacitors 3c49 , 3c50 & 3c51 2.2 uf I’ve had these cause a similar effect on a GEC solid state set 

@the_teleman

Well, there's no substitute for experience, or lack of it in my case. Thank, you. 👍 

I was working my way back from the RGB outputs, through the drivers, I had got back to the TCA800, and replaced it, without any result. At which point a lot of arse scratching ensued. I think it would have taken me hours to get to those three caps as looking át the datasheet 2,4 & 6 are not defined.

I pressed Teletext and all I had was garbled top line.

Pressed page, 100, and I can see IMOGen displayed at the top and the page counter is going nuts cycling

Tested it with live teletext via Pi, it sees Ceefax loading page and does the same thing, cycling page number, but never displays full page content.

I guess there's a teletext panel fault, now I'm really in trouble as there's no data for this panel and I've no idea where to start.

Having now got a perfect picture I would be investigating what caused you to think the CRT was low emission, has the tube woke up now after passing current or was there something wrong with the test, I would test the CRT again and see what result you get. 

Excellent. Just typed a whole list of questions, just thought I would refresh the page and voila! Looks like there may be a problem with the zero button on the RCU as you should have P100 top left. Try a page without a 0 in it if there is one in the Imogen text stream.

Posted by: @jayceebee

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Looks like there may be a problem with the zero button on the RCU

Zero is fine, just operator error not having used an ultrasonic before, you have to be patient, unlike infrared.

Some info on the inner workings of the XM11 here

Interesting, with the good picture I checked the RGB cathode outputs they are now just R-21V, G-21V, B-18V that still seems odd!!!

Based on the trouble I had with my Granada badged Salora 20L30 and its teletext board, I'm suspecting the problems on the Rank board may be similar.

Looking at the state of the ic legs, I'm guessing the sockets may well be as mucky. I'm not proposing to remove and solder them direct, but I may remove all the chips to clean and squirt some servisol into the sockets. There's quite a lot, and I'd worry about breaking a leg on removal, so I'm going to continuity check the leg component side through to pad print side, if they all buzz out then I will leave well alone.

Just out of curiosity did you test the value of those Chinese capacitors you fitted first as they look well fake.? 

Excellent progress Chris, The tube looks fine. I just don't trust emission tests especially B&K. My mate Mick has one and often we found tubes that test poor are fine.  As far as mono are concerned they often test almost no emission! You probably caused the tube to pick up just by running it on the tester. I have run poor tubes with the brightness turned up full and 7 volts on the heater they almost always pick up. My Decca 30 is the one exception, that stays only fair but it is a re-gun of indeterminate parentage... 

IC holders especially on Txt panels were always a source of potential trouble, I read an article somewhere quoting the reliability of certain chips, put it in a holder and the potential for faults and failures increased multitudes. 

 When I briefly worked on industrial electronics the firm I worked for forbid the use of IC holders and didn't like plugs and sockets or edge connectors in their designs past the development stage. 

I'm not sure I would spray the holders I would carefully remove any chips with suspect connections and clean the pins with a fibre pen you could use a scrap chip with it's legs roughed up to push in and out of the holders to clean them dry. Just a thought...

Rich

Posted by: @michael-dranfield

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Just out of curiosity did you test the value of those Chinese capacitors you fitted first as they look well fake.? 

Hi Michael,

yes, I tested capacitance and ESR on two devices as well as reaction to rated voltage. Although not actually 10K they were close enough at 9.7K, the ESR was very good and no leakage at a little over the rated voltage.

The one that was in circuit, had almost doubled in capacitance, was high ESR and electrically leaky unable to attain 16V.

The 10KuF 16V +ve is directly connected to pin 1 (input?) of what appears to be a 3-pin regulator, although I've no idea what it is, as it's labelled 7713.

Edit: Actually what I thought to be a "3" is an "8", making it a 7718 18V regulator, that makes sense 12V & 18V supplies to this board

On the other side of the board there is a 7812 regulator, the +ve of a 4700uF 25V electro on the input pin 1.

Posted by: @michael-dranfield

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Having now got a perfect picture I would be investigating what caused you to think the CRT was low emission

The B&K showing low emissions, that did not budge after one hour of running. As previously stated, I'd never seen one stay so low in all the CRTs I've tested on this.

@michael-dranfield

Hi Michael, I was wondering when you got your BC6333 version of this receiver from the local TV rental company, did they by any chance supply it with the service manual. Specifically the data covering the teletext/decoder hookup circuits.

I don't think so, I have loads of bush service manuals but never heard of A T12, what might be of some use to you is the wireless world circuit just incase it has the same Texas text panel??

It must be a very uncommon model, a google search brings up nothing it's obviously based on a Z718 but why Rank gave it it's own chassis number is a mystery. Has anyone got the red books for 77/78?  Did Rank produce a Z718 teletext chassis? if so is the service info for that anything like this set?  

There is a servicing article in the August 1982 edition of  Television magazine which clarifies the production date and the use of the inline Toshiba tube but no mention of a Txt version. The second part of the article states that the A1 pots on early models were 10 Meg and on later models 2.2 Meg on later versions, this may give a clue as to the age or production date of this set. 

I believe it is game over for this Rank AC6333, with regard to it being a working-integrated teletext receiver.

@jayceebee triggered a memory this afternoon that made sense of the problem I have with this set and teletext.

Some background

I have in my collection the very first set top Teletext decoder box, namely the Labgear 7026. It was released for the launch of the Ceefax service, not cheap at £399, a lot of money back then. It's the one shown in a demo on a Pebble Mill episode, featured in a thread on the forum and on YouTube.

At the core of the Labgear 7026 is a Texas Instruments "TIFAX" decoder board, these were the first ones which used a Texas Instruments TIFAX (74S262) character generator and were easy to spot because of the curious designs of the 6 and 9 characters. The version of the board in the Labgear is D22N700 Issue 4. See above last photo.

I remember being told by an ex member who was well versed in Teletext, shortly after its release there was a standard modification to the Ceefax service that caused this version of the Tifax decoder to be incompatible with the service, and therefore I was wasting my time trying to get the Labgear working with my IMOGen.

Sadly, the Rank AC6333, uses the exact same decoder, see below.

Shame, but there we have it, nothing I can do.

There's nothing to stop me connecting one of my other set top Teletext boxes to it, I have two AYR and one Radofin. It can at least pretend to be integrated, at least the TV is working and restoring the ultrasonic remote was great fun.

A real shame but the journey was fun. The Tifax XM11 had a short life, I remember not that long after the first 9600 model was introduced with text and getting complaints from customers. On one of the test pages, I think P198 it displayed a message at the bottom of the page "This is not a full spec decoder" and this was well before the Mullard/Philips VM6101 appeared. The XM11 couldn't do double text height and background colour, Texas released an updated board the XM12 but I'm not aware of it being used by any set manufacturers.

During the sets service life fitted with the XM11 I wasn't aware of any that stopped displaying pages, the change in the data stream specification must have been pretty late.

It never rains but pours, the fault that was cured by changing the decoupling caps to the TCA800, has returned. It's going to be one of those sets.

Hi Chris is the earth connection to the decoder sound? Sometimes it is just relied that the print will make a connection when up against the chassis. For instance on the Pye hybrid CDA and as we know it often wasn't good enough..