Rank Arena/Voxson colour set

[Jimmyhaflinger]

hi,

I have this Voxson Cromorama set that belonged to my grandparents, and i'm trying to revive it...

I know it's a Rank Arena set rebadged for the Italian market as I saw an ad for the British version somewhere.

The problem is, it worked until a few years ago then the EHT rectifier blew, now I have fitted a replacement rectifier but when I tried to turn it on I heard a brief burst of line whistle and static from the speaker then the mains fuse blew.

What should I check first? is there a service manual available online? (I don't know the original Rank Arena model to search for it)

[Peter.N.]

Sounds as though its suffering from damp, I would give it a thorough drying out before you do anything else.

Peter

[dazzlevision]

From the look of it, I'd say it probably has the Rank T20 or T22 chassis inside. The chassis type fitted is usually printed on the label stuck onto the back cover. Failing that, take a picture of the chassis and post it here.

[MALC SCOTT]

Looks like a Z718 chassis, Malc.

[Welsh Anorak]

I'm pretty sure this is a Z718 which has the odd single-stick rectifier on top of the LOPT. I'd guess the original has taken out the line output transistor. It's an unusual arrangement with an unregulated simple HT supply, the regulation taking place 'below' the line output transistor. As the LOPT has an EHT overwind things need to be very dry here or else arcing can occur.
I may have a manual if you have no luck elsewhere.
Glyn

[FERNSEH]

Is that the moulded cabinet they used for the Bush BC6100? An 18" CRT model that employed the Z718 chassis.

[Jimmyhaflinger]

Originally Posted by Welsh Anorak

I'd guess the original has taken out the line output transistor.

that looks like the one i have...

I briefly tested the output transistors with a DMM and they don't seem to be shorted, the set is quite dry as it was stored in a heated room.

I also have a parts donor chassis I took from a destroyed set (I took the EHT diode and focus module as one piece from this chassis) but I can't try to swap the whole deflection board as the print on the spare board is cracked and there are several broken coils etc.

[neil29]

Yes that is a Z718 chassis set as I have one here that differs mainly in the badging but is otherwise identical.

Cheers
Neil.

[hans]

Do you have a diagram for the set?

This set doesn't have separate power supply like most other sets. The mains is regulated in the line output stage.

[Jimmyhaflinger]

i was able to get the set to power up again this evening!

as it turned out the big smoothing capacitor tested good with an ESR meter but shorted when the full HT voltage was applied to it
luckily the smoothing capacitor from the donor chassis was still useable

the set worked for about 15 minutes with a reasonable picture, then it suddenly lost green drive... now i read about 145v on the green RGB amp output and i get a bright green screen if i short the green and blue outputs together, so hopefully the CRT is still OK

is this a set where the RGB difference signal is fed to the grids and the luminance signal is fed to the cathodes?

[Jimmyhaflinger]

replaced the TCA800 and the green drive is now working as supposed!

i'm wondering why it failed suddenly after 40 years...

[Welsh Anorak]

It won't be the only thing that fails after 40 years!
Well done for finding the capacitor - it's the sort of fault that has you chasing round in circles as it tests OK when cold.
They used the 'new' PIL tubes and always seemed to have a good picture and rarely failed - I think they used Toshiba tubes which would make sense given their relationship with that firm.

[Jimmyhaflinger]

The tube is a Toshiba indeed, this is a high-hour set but the picture is still reasonably bright and focused.

i still have a couple of faults: the dynamic convergence panel is dead, the controls are all inoperative, being an inline tube, the convergence errors are limited but are clearly visible when watching from a close distance...

also the set is displaying alternating red and green lines on saturated colours, especially blue, maybe it's a simple PAL set? otherwise i think there's something wrong in the demodulator

[slidertogrid]

The Z718s are "proper" PAL, but both the A823 and the and to a lesser degree the Z718 decoders suffered from this problem if not set up correctly. I remember spending some time trying to cure this type of problem on an 823 years back. You could try a slight tweak if you make a note of original positions of any pots or cores first. They can then be easily returned to their original setting if no improvement results.
Nice set, I haven't seen one in decades!

Rich.

[Jimmyhaflinger]

These were quite popular here in Italy as they were relatively inexpensive sets and were marketed right when official colour broadcasting started in 1977

[Welsh Anorak]

Hi
With the decoder fault I'd remove, clean and replace the ICs on the board if they're in holders as many were on this model. If no improvement then alignment is called for which isn't too bad on this set, though make sure the LT voltage is accurate first.
Not sure about the convergence though - I'd start looking for a disconnection to the board. I don't remember them doing much, though I would expect some effect.
Glyn

[Jimmyhaflinger]

the TCA800 Ic had already failed while i was testing the repaired set and i replaced it with one taken from the parts donor chassis, maybe this has something to do with it?