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

Ah, I was wondering how they did the keyboard. The Rank transmitter circuit is pretty much the same as the Thorn versions which also used the SAA1024, there is only slight differences in the way the output is fed to the transducer. I'm pretty sure they would be interchangeable.

Have a look at this link for a selection of 40KHz transmitters and receivers of various sizes. I certainly wouldn't order semiconductors from AliExpress but doubt you could go wrong with these.

I see your remote has a different type of auto transformer fitted, mine has a mullard potcore. 

Irony alert! Invested in an ultrasonic cleaner to clean my ultrasonic remote PCBs.

I've no idea if it will do the job but thought it worth a try, as it would save having to remove those 25 brass pads, and the associated risk of the breaking the two retainers on each that anchor them to the PCB. It may not work, and I may end up having to, it might even take a couple of goes, we shall see.

First 30-min session, fingers crossed.

p.s.

My main worry, it looks like that highly corroded pad might have been eaten away by the battery acid. Sods-law it would have to be the "zero" key and not the opposite one which is the "clear" key. I need the former, and could do without the latter.

Well, it cleaned up nice and saved me loads of time not having to manually perform the task.

As I mentioned above, my concern was for the "zero" pad, I think I'm going to be OK. The two pads are intact, therefore the brass prongs will make contact. If you look at the last photo, I superimposed the brass contact and ghosted the layer so you can see where the pads and contacts meet.

The proof will be when I reassemble and test the zero button, I'll use my frequency counter to see if it generates the expected 43,990KHz.

I'll pop the other board in the cleaner, but I will remove L1 just in case.

Removal of the crusty, acid encrusted solder to outer black ribbon connection, also repair of destroyed trace using track repair tape, and re-tin of traces.

I also swapped the position of the brass contact pad from button "Mute", to the button "zero" pad, the sides of the original brass "zero" had disintegrated due to the acid, thus loosing rigidity. Zero will get much more use than mute ever will.

Removal of the old solder to the 12 pads for the ribbon cable was very difficult. The battery acid had changed the composition of the solder, it appeared non-conductive, very resistant to heat, and like a rock (see pic 3). Thankfully, with lots of flux, the Metcal could supply enough heat to dislodge it.

It's not a pretty track repair, but under the circumstances better than it was before. I'm just glad the damage was confined to the one button, it could have been much worse and widespread, so I count myself lucky.

@michael-dranfield

Despite having repaired the damage, I've now filled myself with doubt.

Michael, is there any chance you could disassemble (sorry) your Bush remote and confirm the track underneath the "Zero" button. Due to the acid having eaten away much of the track, I'm now thinking there should be a join, as shown below.

This is what I've now repaired the missing trace to look like, I believe it to be correct.

While I await confirmation about the pad above, today I will be removing all the components from the main remote PCB, prior to thorough cleaning.

All the solder will be removed as it has been infected with the battery acid,  and its composition seems to have changed to rock! All the left hand side resistors are in poor condition. I also think the ic socket should be replaced, pin 14 of the ic does not have continuity through to the print-side. This could be due to solder, socket or i.c

Once all the components are off, it will have a couple of cycles through the ultrasonic bath. I've documented the following for my own sanity and for documenting the remote, as the values differ from the Rank service engineers guide to teletext handbook.

Posted by: @crustytv

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While I await confirmation about the pad above, today I will be removing all the components from the main remote PCB, prior to thorough cleaning.

Try this.

Excellent, Yay! I was right to doubt my first repair and correct it. My second attempt matches yours exactly, Phew! Thanks Michael, I can relax on that one now. 👍 

However, the state of the main PCB..... that battery acid really did take its toll. As suspected, the IC socket had been damaged, corrosion through the pins. I've also lost two pads, 2 & 12. Getting the rock off, I hesitate to call it solder, was more like shifting excrement from a blanket. What's worse, rat pee or battery acid? Both seem to change the surface of solder & traces.

Now for the ultrasonic bath, likely a few cycles too.

After a couple of clean cycles in the ultrasonic tank, most of the resist had dissolved away in the cleaning fluid. I was left with little choice but to just tin all the traces. I'm looking into buying UV cure green mask that you can get on Amazon, I shall wait to if the remote functions, then decide.

New transducer installed, and I was not happy with the SAA1024, considering the damage to everything caused by the acid, the legs may have leached into the package. I therefore installed the M1024B5 from the same remote the transducer came from, I believe to be equivalent. Also, new IC socket, new 220K 1/2W 5% resistors, the rest were OK.

Not much to do now other than thoroughly clean the case, join the two boards together, then get out my frequency counter and pray the TV gods smile upon thee and I have some life.

Coming along nicely. Just to be clear the output is not a continuous frequency but bursts so your frequency counter could be confused. If it works you will hear something, not the 33-43KHz but the burst frequency.

There is a very good write up in TV mag of this system, January 1978 page 139.

Aww, that's mighty disappointing, nothing, as Dr McCoy would often say "it's dead Jim".

Well, it appeared dead, no LED and I cannot detect ultrasonic via my ear or counter.

I am developing .445V on all key depressions measure at base of VT1, except on keys "1", "0", "vol -" & "col -".

Strapped in a new LED, so the old must have died.

So, that's made sussing the working keys easier and confirms as above those not working. I will have to look under those 4-pads for the cause.

VT1 tests OK

OK, I was wrong it is working I just me. This is my first real-world interaction with ultrasonic remotes, so not used to what to listen for. I can now hear the faint tone, some are easier to hear than others. I've also connected my 200MHz scope, and it picks up the key depressions too.

I have also confirmed there is no tone on the keys mentioned above. So I'll be investigating those tomorrow. When all said and done, I'm happy with the way this has gone, after sorting (hopefully) those dead keys tomorrow, it will be time to get the TV up on the bench and see what's what with that.

Don't forget the ultrasonic transducer needs about 100 volts to drive it correctly and for the keys I would recommend a fiberglass pencil. 

Button 1 & 0 now working, just the vol- & col-

All the brass contacts are fine, it traces underneath that have been damaged by the acid leakage. When I put the control board in the ultrasonic, I did not remove all the brass contacts, I didn't want to temp fate and risk the little tabs. Of course, this did not allow me to see all the problems underneath. For the most part that worked as I only ended up with four pad not functioning, just these final two to fix, the remote is then finished.

Later this morning, the TV will up on the bench for an evaluation/inspection and documenting of the state of play on all boards. Then decide the best way to wake this up after 45-years of sleep, OH, and I will be reforming the main caps first.

Still not sure what circuit is best to follow with this being a T12A chassis, the Z718 or T20 manuals or neither. I will have to see what tallies up with each of those two manuals.

@crustytv Incredible that you are able to restore that handset Chris, I would have expected it to be beyond repair.  I can't say I remember a T12A chassis. From your pictures it looks more like a Z718 than a T20 to me, Does it have a large overwind and a stick rectifier or a more conventional secondary and Tripler?  From what I can see of the power supply it looks more like the one used in a Z718. I didn't see that many of those. The T20/22/26 was more common around here especially after the Co-op released a load of ex-rentals into the wild! 

Hi Rich,

yes, when I first looked inside the remote and saw the level of damage from the acid, I was horrified and thought the same, this does not look good.

That thought soon vanished as I remembered everything can be fixed, and even if the board was BER, I could always copy it and get another made. That fortunately was not required, and careful cleaning and track repair has restored it to full operation. I've even ordered a green UV green solder mask kit to make the tinned PCB side look neater. All screws holding in the PCB and case have also been replaced.

Anyway, I'm sure you're all bored with this remote control repair and all the photos, so to close this phase I can finally say the final pad repairs are done, and all the remote buttons now function. A coffee, then the TV will be up next, so stay tuned.

Well done getting that remote working! Those ultrasonic cleaners are really good, I have one which I don’t use enough these days, mostly because I’ve put it somewhere hard to get to! I’ve even used mine to clean a really knackered CD player laser (it was junk anyway!) that was full of what looked like plaster dust, and wouldn’t play, but came out of the cleaner working perfectly! I also have a nice Sony radio that had severe battery leakage damage, it’s a right pig to clean up, that was on a double sided PCB, where it ate through the connections between each side of the board, I used conductive silver paint to sort those out, and to fix dead keys. Sadly the battery goo is still eating its way through the radio, as it’s gone haywire again! Maybe time to revisit the poor thing!

One thing I did think might be useful for you if you couldn’t revive some keys, some small SMD tact switches, they might just fit under some of the keys! I had some that came from dead Nokia 9210 phones, they were about 1mm tall, metal body things. 

And so it begins.......The TV resurrection

Here are the detailed shots of the internals, another chassis baptism for me, I've never worked on one of these before.

From the last photo, we can assume there were at least 534 others, who knows how many in total.

Some of the panel codes I’ve found thus far, it's awfully crammed in there, bet these were (not) fun in the field.

• Line Output Panel 3703 (Z904A)
• Scan Drive Panel 2802
• Decoder Z905D
• Power Unit Z907
• CRT Panel Z921A

P.s.

Anyone know what the UK equiv was of the Toshiba Blackstripe 560A KB22? Was it A56 510X?

It looks like a development of the Z718 I don't know what differences there are though. I don't know for certain but I don't think the Toshiba 'Blackstripe' had a 20AX equivalent, the scancoils are fitted with wedges which I don't think the 20AX coils were. Hopefully though your tube will be OK?!