CTV 1975 22" Granada C22NV2; Tandberg CTV2-2

Its not atcually a delta cap, it only contains one capacitor and the two outside legs are internally connected together, however a lot of these contenental sets were fitted with a yellow capacitor that was only rated for 220vac and they use to go up in smoke, the reccomend replacement was a gray type rated for 250vac,I would guess its drawn that way as this is how it appears on top of the cap itself. 

A bit of help with C978 please.

I am presuming that the 6.8ohm resistor , 10uh choke and C978 are there to remove any switching noise from the output of the bridge rectifier,. It uses BY127 diodes which are slow and produce noise that could affect the timing circuits for the SMPS.

C978 is made in a way that the connecting wires are as short a possible to give the best decoupling at the “hash” frequencies being produced by the bridge.

The bridge does have individual capacitors across the diodes but perhaps that wasn’t enough.

Does this sound reasonable, or is there another explanation for C978 design.

thanks.

Posted by: @michael-dranfield

Its not atcually a delta cap

The very first time I came across this type of “three-legged” looking capacitor was four years ago. I was working on a 1977 Thorn 3734, 9600 chassis, I asked what on earth it was and how to test it. I was informed to look up 'delta' filter capacitors, then all would be revealed.

https://www.radios-tv.co.uk/community/colour-television/1977-ferguson-3734-colourstar-thorn-9600-chassis/paged/2/#post-16144

Thanks for setting the record straight. All my stock (white, grey & yellow) are 250V, even the Yellow ones I have are 250V.

@nuvistor  This is what I think, and this is only my personal opinion , I could be wrong ,  as this is only a 1uf capacitor with both outer legs connected together , the mains goes in one leg and out the other so removal of this part would make the set dead, I have known many engineers who see a faulty mains filter cap and just snip it out , never to be replaced ,so removing this 3 leg capacitor would necessitate replacing in in order to get the set going again .

Hi Chris.

In our service dept here in Kilmarnock during my 18 years with Clydesdale we did a considerable number of outlying farms and small communities. These often had power cuts, brown outs and many other power issues. There were many well do do customers that bought Grundig, Saba and Tandberg. The sad fact was the Grundig 5011 and 6011, Saba and CTV2 Tandberg didn't cope well with the mains maladies. Tandberg were aware of the issue and their technical rep admitted that the PSU didn't like sudden fluctuations in mains volts or spikes. Tandberg came up with a repair kit that was also a modification and this was indeed a cure, whether the later models had the mods I'm not too sure, it's too long ago. Both the Grundig and Saba thyristor line stage sets would blow high wattage resistors but were considerably worse where the mains was inconsistent or had spikes like on farms that milking machines produced a lot of spikes etc. These problems were less of an issue with hybrid CTV, the ITT KB CVC5 and 8 being the preferred set in these locations. 

Hi Trevor,

thanks for the insights, it's always great to get first-hand anecdotes from those that had to deal with these in the field.

I also have the Grundig 5011 in my collection, hoping to get that up on the bench when time permits. I've read horror stories of that particular model, if not serviced properly, burning a bloody great hole in the PCB! I've two spare 5011 chassis, and one has indeed suffered just that, a great source of spares though.

These Thyristor line stages are fairly new to me, but I enjoy the lessons all these TVs give me, both UK and continental. Thankfully, I have the luxury of enjoying the various TV developments at my leisure, unlike you guys who had to deal with all the challenges in real-time, in the field.

The new filter cap arrived for the Tandberg CTV2-2, I couldn't get a 400uF so 470uF the next best equivalent, and in case anyone is concerned, I did ensure it was the high ripple type. I can now get the PSU up on the bench and give it a thorough servicing. Fingers crossed the Thyristor is OK, as I don't have any BRY55's in stock, and thus far I've not found an equivalent, but maybe any 300V 800mA thyristor will do, perhaps a BT100.

Edit: Just found a few possible thyristor candidates, should the BRY55 be cooked, so ordered a few of the various types.