CTV New Additions; Ferguson, MultiBroadcast & Bush

@jayceebee Ah, the 8940 - we had one - DER badged I think - just after all their shops near us changed to MultiBroadcast. An adequate, and trouble free, machine, but the wired remote control was a bit of a pain.

Almost a year later, I was looking on eBay when I happened upon a rather interesting ultrasonic remote. The seller had no idea what TV i might belong to, but did provide some photos. When I saw the PCB with the 'Z' prefix, I knew instantly it was RBM. I then thought, "now wouldn't it be cool if that was for the 22" Bush BC6378A T20 series. When I checked the manual, it only bloomin well was! An instant hit of buy it now, quickly followed.

Wow! Is all I can say, wow! I've had some luck, like finding the remote for the HMV 4000, long before the TV, and now I have the ultrasonic remote for the Bush, which I never thought I'd ever find.

It appears complete and does come with a spare board and another transducer, although that appears to have two legs not one, which the remote unit has. The remote's transducer with the single input, is disconnected, so I'm wondering if it's fault and that's why there is the spare that has two inputs. We shall have to see, oh goody more ultrasonic fun and games to be had.

In case you're wondering, yes, there is only one button on the remote.

However, you do have control of channel change and muting only. It requires a short press to provide a short burst signal lasting from 250mS to 1 second, with each consecutive burst changing channels in sequence. Sound muting is accomplished using a longer signal of about 2 seconds; a further short burst signal restores the sound but does not change the channel.

I bet the consumer had great fun trying to get the hang of that!

I bought 4 of these remotes years ago from ebay but one was really tatty so i just kept the pcb out of the bad one but i still have the others.

Cheers

Neil. 

Both boards have their own issues, so it was a case of making one good from two.

Testing each board, one was only producing a polarising voltage of 70V, the other 160V, when measure at the cathode of 11D2. According to the book it should be 270V, so 100V down. One board had a cracked ferrite on 11T1, the other not, using the board that had the best polarising voltage I made sure that had the best 11T1.

I then tested the output of the transducers, one measured much lower than the other. Measuring voltage across each in situ, one gave 85V and the other transducer was 187V, book states no less than 285V, so again that is down 100V.

Now I have a board that produced the best polarising voltage (160V), and best output voltage (187V). After making one good board, I then put it on the scope to see if it was actually producing a signal.

The scope could see the remotes ultrasonic waveform, it was at 30.25kHz. I just needed to adjust 11T1, so it read 40kHz. I'm not sure if there is a further problem to find that is resulting in the reduced voltages. There's not a lot on the board to go wrong, 1x transistor, 2x diodes, 2x resistors, 5x capacitors and one electrolytic. The two resistors are innocent. Do transducers fail? Do they go low voltage, as I've no idea? I'll have to get the Bush up the list soon and see if this now works with the TV.

Posted by: @crustytv

Do transducers fail? Do they go low voltage, as I've no idea? I'll have to get the Bush up the list soon and see if this now works with the TV.

I have to say I’ve only ever had replaced them where they obviously have been in contact with liquid, dunked in a cup of tea or worse😱. Can’t remember ever having to change a receiver in a set.

I must say having never been exposed to ultrasonic controlled TV's I was amazed to find such voltages being generated inside the hand unit, I just had no idea.

Posted by: @jayceebee

I have to say I’ve only ever had replaced them.

That prompted me to look for spares, other than buying up vintage ultrasonic remotes to harvest for parts. I found Digi-Key in the UK sell them.

https://www.digikey.co.uk/en/products/detail/murata-electronics/MA40S4S/4358147?utm_adgroup=Ultrasonic%20Receivers%2C%20Transmitters&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Sensors%2C%20Transducers&utm_term=&productid=4358147&gclid=CjwKCAjwmJeYBhAwEiwAXlg0AVqq6viZYR6Fh9xgW7FPwu7tSsBOLzh18LAZN8NQJA04CR29m6gcNxoCQr4QAvD_BwE

Unfortunately, I don't think those would withstand 187V+ across them. They do offer two other types capable of 150V, but they only go up to 39kHz. Anyone aware of other sources?

There is a missing word in my reply “I’ve only ever had to..” but I think you got the gist. You could try one of those you linked to and experiment with the value or 11R2?

After having a rummage I’ve found a spare transducer I had but I don’t know if it’s a TX or RX. I’ll drop it off with a couple of 7400s I also came across.

Well, yet another ultrasonic that's not working, I'm not surprised though. As I said above, the output across the transmitting transducer is almost 100V down and the polarising voltage at D2 a little more. On top of that, the Bush has an EW fault.

Re: the Murata transducers, piezo can produce/withstand pretty high voltages so I'd give something from Digikey a try - I have a business account with them and their service is excellent. However... the MA404 you linked to will only withstand 20V p-p. 

Re: the T20A - I'll not tread on the toes of those wiser than me on those sets, but usually there's a diode connected to the lot that forms part of the E/W modulator circuit and I've seen them go o/c on professional picture monitors with the same result. 

Posted by: @cathovisor

usually there's a diode connected to the lot that forms part of the E/W modulator circuit and I've seen them go o/c on professional picture monitors with the same result.

Being a curious old crusty, that piqued my interest, so hunted out the T20A cct, to see if there were any. Not as simple as I thought, no single cct block (à la Thorn) but E/W appears spread about, E/W breathing? I've identified a few, I wonder if these relate to your hunch.

I'll start simple and look at 4RV1. 😉 

I'm looking askance at 5D6 and 5D7. Dunno why, just am.

I should hasten to add that in no way is this a full-on Cathovisor Vulcan Mind Meld with an ailing Bush, but... 🤣 

Posted by: @cathovisor

full-on Cathovisor Vulcan Mind Meld with an ailing Bush

Oh dear! That conjured up a Viz type image of Spock and T'Pau 🤮 

Unfortunately, neither of us hit the sweet spot, both D6, D7 and 4RV1 are innocent. 4RV1 did have an effect, it sorted of evened out the middle of the left and right side, but the top and bottom of left and right side was a mess and uneven. Boy, those diodes are monsters, 600V beasts!  I shall study the cct and pick my next candidate.

Hi.

Off topic I know but your display is impressive Chris 

Do you do rental terms for pensioners? 😆 😆 

As our man in the last TV Shop in the North would say, GLASNOST! This was fun and an own goal.

Ok after just removing the diodes for testing and finding them good, I set about testing voltages. Taking readings, I find the width modulator circuit appeared to have the correct supplies +200V and +36V, and 16V at 4VT18 present. As mentioned above, I'd checked the diodes, which tested good out of circuit. The voltage however, at the cathode of D7 was just mV, curious, something not right here! This is where I made my mistake, looking for complex reasons for the EW fault, completely missing the simple. Fortunately, I had a chat with John, he explained based on the info I gave him, it could be any of the transistors in the modulation cct, and to check each of them methodically, but...... had I checked the 4RV13 first?

I hadn't, this was one of those PIHER sealed pots not a skeleton, I had not given it a second thought, as they so reliable, aren't they?  I've learnt to follow John's hunches, so squirted in some servisol into it, rocked it back and forth, then powered up expecting no change. OMG! How foolish was I not to check the preset......egg on face! 😊 So will I suspect ALL presets in future and look for dead-spots, Oh yes indeed! These are the types of faults that get locked in memory, adding to the list of experience.

So my apologies also to @cathovisor, his analysis......

Posted by: @cathovisor

I'm looking askance at 5D6 and 5D7. Dunno why, just am.

Mike was indirectly correct. 👍 clever cloggs.

Although the diodes were not faulty, the voltage readings I later took, meant they were telling me they were not happy due to something down stream. Mikes hunch was spot on, and I'd wasted time by only initially testing them, not voltage mapping them.

I'm super impressed with a 20AX T20A, what a phenomenal picture! Yes, it still needs a little tweak, bottom left, but this was pretty much as it came up.

One of these was my brother's first colour TV and also the set I learned about the 910R resistor giving no results. I too was very impressed with the pictures but the push-button channel selector became so unreliable it led to the set's demise. It was replaced with a Salora M chassis set. 

There is often a bit of interaction between the control rather like convergence. If you increase the width slightly then you should be able to get the picture edges correct.

My first encounter with the to T20 was due to 5R8 going o/c feeding drive to the base of the line output transistor. it was a pain to find due to the startup sequence I seem to remember. Didn’t see a lot of these but I always found the PSU was quite noisy, the tones varied with beam current.

Posted by: @jayceebee

Didn’t see a lot of these but I always found the PSU was quite noisy, the tones varied with beam current

Ah, now that has answered something that as been puzzling me since last night. With the back off and the set running, I could hear this distinct sound emanating from somewhere within the chassis. My paranoia was kicking in thinking it was the LOPT as allegedly these were a weak point of this chassis.

Thankfully, I have a brand-new replacement in stock should the original fail, as I really like this TV. It looks a much improved version than the RBM one fitted, it looks almost like the Weyrad type but is a Konig.

I've got 5 new ones too. one of which is the same as your one and 2 of them are RBM parts. and there are some scrap boards with lopts on them one of which i used to fix my basic T22. luckily i haven't had to use the new ones yet 😯.

Cheers

Neil.