Granadacolour C20TA5 colour fault

[GadgetM]

Hi, any help would be appreciated here, I have a Granadacolour (most probably a 1979 GEC starline), which has a strange intermittent colour fault. When I switch it on, only the red and green guns come to life, until it's been on a few minutes then suddenly the blue wakes up and then looks perfect. I swapped the tuner/colour drive board with a working spare, so it's not that, I even swapped the red, green and blue wires around so was sending green in to the blue input on the tube board, still no blue, just red and green so I've come to the conclusion that it may be something to do with the main power board, (which I don't have a decent spare for) or worse still... the tube!.

The trouble is, some days it works fine, which makes it so hard to trace.

Any suggestions welcome.

Thanks

[evingar]

If applying a known active (green) drive to the blue gun results in no blue picture content this fingers the tube or tube base as being suspect.

[Nuvistor]

Did GEC and Hitachi have a connection of some form?

If it is a Hitachi chassis with "Quick warm up directly heated CRT" check the chokes on the tube base that feed the heaters. A fault was dry joints on these chokes although the joints looked ok.

[Maarten]

Dry joints or loose or oxidized contacts on the tube base, or a faulty tube seem most likely.

[GadgetM]

thanks guys, I'll try some re-soldering on the tube base (board)

Originally Posted by Nuvistor

If it is a Hitachi chassis with "Quick warm up directly heated CRT" check the chokes on the tube base that feed the heaters. A fault was dry joints on these chokes although the joints looked ok.

Not sure if it's a Hitachi chassis but it is a Hitachi tube. I'll be disappointed if it is the tube, it's not shown any previous signs of aging, still pin-sharp, plenty of brightness etc.

[Welsh Anorak]

Hi
If it is a Hitachi 560EGB22 CRT (or similar)I have occasionally had this fault - sadly it was always the tube. A light tap on the neck may well reveal all. The best solution is to switch on five minutes early!
Glyn

[GadgetM]

Thanks, you're close, its a 510RCB22, still could be the tube I guess, still waiting to have the time to further investigation.

[Clydeuk]

I saw a lot of the Hitachi sets in the 90's with similar problems. From a cold start have a look at the tube heaters, you may see only 2 lit and a tap on the neck may light the third coinciding with the blue content returning. I think the fault is that the heater becomes detached internally, sadly no cure I think the Hitachi tubes were to blame, I scrapped a lot off in those days.

[Welsh Anorak]

Hi
Seconded - I'm almost certain it will be the tube.
Glyn

[GadgetM]

well... the fault has mysteriously gone away, probably not for long, it's done this before. So fault-finding is on hold until it does it again. As soon as I get time to investigate the fault, I'll post my findings. Thanks everyone for the advice!

[Clydeuk]

Well you've narrowed it down to the tube base or tube itself, the visual of the heaters when the fault does show should tell if it is the tube or not since the 3 heaters are in parallel. If it is the tube i guess it's one you can live with if it rights itself. I have a lot of recollection with the Hitachi sets as I obviously couldn't sell them and the picture was usually excellent after a tap on the neck

[GadgetM]

Well, the fault has re-occurred, and it's not going away now. Permanently yellow picture. Tried everything suggested here, not dry joints, tapping the tube neck doesn't work either.

Please forgive my lack of knowledge, but if it was a tube heater issue surely all colours would be affected wouldn't they?

I've tested all 3 colours to the pins on the tube base board, all reasonably similar, even swapped the red, green and blue wires round to check it's not a blue-drive transistor issue, and it's not

Any other ideas, or is a tube transplant is the only way to rule out the tube?

[Nuvistor]

Can see all three heaters lit up? There are three heaters one each for red, blue and green.

[GadgetM]

Not sure, there's only a small area of clear glass, hard to see. Looking at it stood behind the set I can see one strip glowing on the left side, there may be one other underneath (or maybe a reflection of the first) but there's nothing glowing at all on the right hand side of the neck, and yep you guessed it the blue pin is on the right. Does that suggest failed heater in tube? If I know which pins are heaters I could test voltages but they're not labelled.

[GadgetM]

There are 2 pins on the tube base marked with "h", I presume those are heaters, both measure around 25v give or take a volt or two. Surely there should be third one?

[jayceebee]

The three heaters are connected in parallel internally to the two external pins.

[Clydeuk]

As stated the 3 heaters are connected in parallel internally so all connect to the 2 pins marked "h". There is no way to power one (or test one in isolation). The tube, being an in-line type will have the 3 guns side by side, not always easy to see all 3 heaters lit, you have to sort of look edge on looking into the cylinder of the gun, you may be able to see the 2 wires from each heater and the orange glow. It sounds like you've spotted the blue one out though, you can definitely see the 2 heaters on the outer edges, the middle one (which is probably green) is the most difficult to see.

Probably not a good idea to use any more force on the CRT neck to see if you can persuade it, I expect thermal expansion causes it to make and break, maybe it's just shifted further away from its contact now.

I did see a lot of these, they must have had a defect in the machine that welded the contacts to the pins.

[Clydeuk]

By the way the heater supply is usually AC from a winding on the Line Output Transformer, so the 25v reading on each pin I assume that you've metered to chassis ground? The supply must be OK as you'd have no heaters if it was absent, and no raster.

[Maclee62]

I vaguely recall that Hitachi supplied certain replacement CRTs FOC after the guarantee had expired. I think it applied to sets marked 'instaview', and the the new CRTs were 'modified'.

I may have this wrong as I did not stay in the retail side of the trade for very long after leaving college before I went to work for a manufacturer's service dept, (not Hitachi or GEC).

I certainly recall seeing a Hitachi set being fitted with a replacement CRT in the workshop, and I know it was supplied FOC because there had been discussions before the new CRT arrived about how the old one was going to be returned. When it arrived there was an instruction/modification leaflet which required the removal of a choke from the CRT base board, (replaced by a jumper wire I think). Hitachi asked for the choke to be returned as proof that the old CRT had been replaced, the CRT itself went to the local tip!

The 'modified' CRT was no quicker to warm up than any other, which turned the word 'instaview' on the front of the set into a bit of a fib!

Apologies if I have any details wrong here, it was a long time ago and this is the best of my recollection.

[Welsh Anorak]

Hi
You're right - the CTP-220 and CBP-210 (22" and 20" respectively) used the infamous 'instavision' CRT. The cathodes were directly heated which meant a picture from cold in under a second - quite something. In fact I have one here that still works well. Unfortunately most failed after a couple of years resulting in a greenish mess. Hitachi supplied new CRTs for at least five years - more if you talked nicely to them. As you say, you removed and returned the odd little transformer to them, fitted a small green coil and dumped the old CRT. No-one complained of the ten-second wait for the picture to appear on modified sets. Must have cost Hitachi a small fortune! They used the word Instaview on lots of subsequent sets.
Reminds me of a customer we had - a grumpy retired bank manager. Came in complaing of a green picture and what were we going to do about it? I visited the house, and sure enough, a duff CRT. Of course he was furious - Hitachi's name and ours were mud. Eventually we calmed him down, and agreed to collect the set the following Monday for a new CRT amid much complaining that he'd have to pay our (reduced) labour costs.
Come Monday he visited the shop almost smiling. Turned out he'd been burgled over the weekend, and the only thing they'd taken was the TV! The insurance paid for a nice new Mitsubishi.
Of course this doesn't help the original problem - these conventional CRTs were good but did suffer from this problem. I agree it's difficult to see the heaters, but when the blue returns you'll see the difference in the neck. In order to get a meaningful voltage on the CRT heater pins you need a true RMS meter. In your case the voltage is probably right. The three heaters are wired in parallel and fed from a winding on the LOPT via a choke so only two connections are needed.
Glyn