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CTV 1982 Baird 8233 TX10 Teletext

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Jayceebee
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Posted by: @till

I notice the MC14426 integrated circuit.  I seem to remember a special chip was made for single and double 7 segment number displays.

Till Eulenspiegel.

Not sure it being special, If I remember correctly The TX10 used an MC14493 for a BCD to seven segment LED driver, the earller 9600 from which this sweep tune board was developed may have been an MC14511.

Anyway, the training we had on BCD gave me a helping hand when I moved over to EPOS for setting SCSI HDD device ID jumpers 😀.

 

John.

 
Posted : 07/02/2024 5:40 pm
Till Eulenspiegel
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Correction to my previous post.  The MC14426 is the tuning memory IC.  Available from Donberg.        Semiconductor: MC14426 (MC 14426) - TUNING MEMORY SYSTEM... - UK (GBP) (donberg.co.uk)

The seven segment driver is the MC14493.

The LM1017 and SN29764 are similar ICs.

SN 29764, Tube SN29764; Röhre SN 29764 ID40404, IC - Integra | Radiomuseum.org

Till Eulenspiegel.

                                                                                            

 

 
Posted : 08/02/2024 11:32 pm
WayneD
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So, about half a bottle of white vinegar and a lot of cleaning of the sweep tuner board I spot some broken tracks:

Screenshot 20240215 214254
Screenshot 20240215 214332

A considerable amount of more cleaning with isopropyl alcohol, some warm soapy water and a thorough drying and some track repairs: 

Screenshot 20240215 214442

I've added some long wires to where the battery was as I'm not sure how many cells the back up battery is supposed to have (it was just a blue-green mess) so I can check with the meter. Also I'd like the new battery to be installed well away from the boards! 

Reassemble and...

Screenshot 20240215 214520

Success! It found the RF output of my 90s Mitsubishi VCR instantly! 

The battery connection is showing as 4.9 volts. As the original cells were Nickel Cadmium they would have required 1.6-1.65 volts each for charging so this tells us that it uses three 1.2 volt cells. Nickel Cadmium cells are obsolete and very bad for the environment (not to mention leaky and destructive) but the modern replacements Nickel Metal Hydride 1.2 volt cells should be fine for this. I was considering a few options for this but then spotted these in B&M:

Screenshot 20240215 214418

 

 
Posted : 15/02/2024 10:09 pm
slidertogrid, Doz and Lloyd reacted
Jayceebee
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@wayned The original NiCad was 1.2V so only a single cell is needed. Well done for getting it going.

John.

 
Posted : 16/02/2024 9:05 am
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Arc De Tripler
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Wow... this thread is making me feel warm and fuzzy! 😊 

The TX10 (and the later TX100's) were the main stay of our rentals for quite a few years!

The less said about the ICC5 (and it's later stablemates) the better! The mere mention of those model numbers still cause my old boss's leg to shake and break out in a cold sweat... they were a terrible rental proposition!

The focus units on the older metal chassis TX10 were a regular issue, especially amongst customers who smoked heavily and used paraffin heaters during the winter months... quite a healthy 'crack' when they arced out. Not so much of a problem when the taller, modified unit came out; I always kept a couple in my tool case!

Damp flats and houses caused us a lot of EHT related issues... it wasn't unusual to see the damage arcing under the EHT cap did to the glass on the back of the tube!

Mains on/off switches were another common issue... some with a hole burnt through the side! I remember there was a recall but not sure now if that was only the TX10 or the TX100 as well? I do remember, given the amount we had out on rental, I was kept pretty busy.

Apart from the frame output chips and the dreaded back up battery, they were a pretty solid old work horse.

Gawd bless 'em! 

 
Posted : 16/02/2024 11:54 am
slidertogrid
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We would usually sell our ex-rental sets retail if they still had a useful life left in them or scrap them if BER, but in the very late 90's we often had a glut of sets as new ones went out and also had an ex rentals that still worked but was deemed too old or not good enough to sell.

At this point I started putting them to one side and once a month a trader would take the lot. They didn't pay much but it was better than skipping them which cost me every time the skip was emptied. 

Written off customer repairs were often disposed of the same way. But guess what? The trader would take Ferguson TXs but not the ICC series! ICCs and Amstrad / Fidelity were the only sets he wouldn't take. He said they were unsalable such was their reputation!  The only ones we had were customer write offs or part exchanges so not a large amount. I took great pleasure in throwing them in the skip, if you put one in the skip screen upwards and then dropped another on it screen to screen there was usually a nice boom as one or both of the tubes imploded. Just a little satisfaction! 

 
Posted : 16/02/2024 12:25 pm
Cathovisor reacted
WayneD
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Posted by: @jayceebee

@wayned The original NiCad was 1.2V so only a single cell is needed. Well done for getting it going.

Aha! I honestly couldn't tell what it was, it was such a mess. I suppose the higher voltage must be due to no load.

Really couldn't find any information on sweep tuners.

 

 
Posted : 16/02/2024 7:12 pm
Jayceebee
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I could do with a new backup battery for my short term memory these days but here is what I remember how Thorn's sweep tuning system worked, originally called Ramp Tuning. Apart from storage two ICs did the bulk of the work. A narrow 24 pin device and another 16 pin, could you refresh my memory on the chips types present?

On pushing the red search button the tuning voltage ramps up form 0 to 33V and the main IC looks for valid sync pulses. When sync is detected the rate of ramp voltage increase slows dramatically then the IC looks for the S curve of the AFC correction voltage. At this point after the AFC goes through the centre of the S curve the ramp voltage is stepped back a few mV and the value is stored in RAM for the program selected, AFC is now fully enabled to centre the frequency of the required channel. It was volatile RAM back in the day hence the need for the backup battery.

 

John.

 
Posted : 16/02/2024 8:26 pm
WayneD reacted
irob2345
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Consider supercaps to replace backup batteries these days. Last forever.

 
Posted : 16/02/2024 9:28 pm
WayneD
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Posted by: @irob2345

Consider supercaps to replace backup batteries these days. Last forever.

After what a super capacitor did to my original Xbox NO WAY!

 

 
Posted : 17/02/2024 5:48 am
irob2345
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You should ALWAYS add a resistor in series with a supercap or a battery, if there isn't one there already.

 
Posted : 17/02/2024 6:31 am
Cathovisor
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Thing is, with a NiMH cell you also limit the upper voltage applied to the rest of the circuit. As far as I know, so-called "supercapacitors" don't.

I'm with Wayne on them - I don't trust them.

 
Posted : 17/02/2024 10:08 am
irob2345
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When a battery corrodes away it can easily go O/C - or it can be removed. There's your protection gone.

It would be foolhardy to rely on the battery in this way. Any self-respecting engineer will add a shunt zener.

 
Posted : 17/02/2024 11:16 am
Doz
 Doz
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Posted by: @irob2345

When a battery corrodes away it can easily go O/C - or it can be removed. There's your protection gone.

It would be foolhardy to rely on the battery in this way. Any self-respecting engineer will add a shunt zener.

Yamaha scooters did the same trick, a high resistance battery would result in all your lights blowing on the way home on a dark night as the lighting magneto's voltage would soar. 

 

 
Posted : 19/02/2024 2:51 pm
WayneD
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Posted by: @cathovisor

Thing is, with a NiMH cell you also limit the upper voltage applied to the rest of the circuit. As far as I know, so-called "supercapacitors" don't.

I'm with Wayne on them - I don't trust them.

You only need to Google "Xbox clock capacitor" to see the damage a super capacitor can do! 

 

 
Posted : 20/02/2024 9:25 am
WayneD
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First glimpse of the teletext board working!

Screenshot 20240220 091219

There is a problem with the teletext board though:

Screenshot 20240220 091234

As soon as I disconnect it and put the bypass on:

Screenshot 20240220 091248

As the board is all Philips blue capacitors I suspect this is the problem.

 

 
Posted : 20/02/2024 9:31 am
Nuvistor and Lloyd reacted
Jayceebee
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The fact that the channel OSD is working means the text board is not too bad. Check the small electrolytics around the VIP (Video Input Processor) SAA5030 first. It would also be a good idea to resolder the leads and clean the text mix and brightness pots on the interface board. 

John.

 
Posted : 20/02/2024 8:53 pm
WayneD reacted
WayneD
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One of these gets smashed up in the last episode of Filthy, Rich and Catflap!

Screenshot 20240317 150906
Screenshot 20240317 150921
Screenshot 20240317 150935

Although it clearly gets replaced with an empty shell and a fake screen when it does get smashed up.

 

 
Posted : 17/03/2024 3:14 pm
slidertogrid reacted
slidertogrid
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🤣 Not even a speaker in it! 

 
Posted : 18/03/2024 11:54 am
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