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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 1st Oct 2019, 12:41 pm   #21
Welsh Anorak
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Default Re: RRI T24E Chassis

Hmm. Those heaters do look far too bright, but I've never had a problem with the tubes on this chassis. What's the make of tube?
Let's try a few things. Do the brightness and contrast controls work at all? You clearly have no red in the display. Mark the position of the A1 control, then reduce it gradually and note the effect. See if you get any red. Voltages on the CRT base will be helpful - you should have around 120v on the cathodes and 300 - 500v on the A1s.
Report back and we'll see what comes next.
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Old 1st Oct 2019, 3:24 pm   #22
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Default Re: RRI T24E Chassis

I've just taken the back off again and had a look round. The tube is a Mullard A51 570X.
Brightness and contrast work well, and the tube still seems very bright. Probably the brightest I've seen on a tube. I couldn't find anything labelled A1, but I turned down the blue and green guns and got a nice pure red raster. I ended up turning the red gun up so instead of bluey/greeny I got a grey raster.

There has been a resistor added somewhere but im not 100% sure where. Could this have been used to short them as Harry W suggested?

I'm not sure on how to get the voltages from the CRT base.

Sorry if I've missed out something really obvious

Thank you for your help. Greatly appreciated!
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Old 2nd Oct 2019, 5:10 pm   #23
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Default Re: RRI T24E Chassis

Ah. The Mullard A51-570x was not a good tube, fitted to KT3 sets in the main, and went low emission very quickly. Odd, as the T24s I've come across have all had Toshiba tubes fitted. It's very likely the tube is low emission and a resistor has been bridged to boost the heaters. Trace back the heater connections and I'll bet you fing a "repair" has been done. I hate to say this, but if that's the case it really isn't worth carrying on with the repair. Sets of this vintage aren't that hard to find.
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Old 2nd Oct 2019, 7:37 pm   #24
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Default Re: RRI T24E Chassis

Hi,

I think it’s a replacement tube as i found a little service engineer sticker saying a resistor had been added to suit the CRT type.

The tube still seems decent in terms of brightness, and now i’ve done some adjustments to the gun controls the colour is much better.

I’d still be interested in repairing it, mainly because it’s been getting on my nerves that I couldn’t find what the issue is.

Thanks
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Old 3rd Oct 2019, 10:51 am   #25
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Default Re: RRI T24E Chassis

The heaters still look too bright to me, and the fact you've had to adjust the drives suggest that it's not a happy tube. I would be tempted to increase the value of the feed resistor until they 'look' right. Voltage measurements with an ordinary meter are inconclusive, of course.
Anyway, you need to find where the RGB signals are. They're fed directly from the decoder IC as far as I remember, and it's likely that the fault is here. A 'scope would be very handy to see what's going on, but if you haven't got one then voltage checks around the chip may reveal the area of the fault.
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Old 3rd Oct 2019, 2:59 pm   #26
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Default Re: RRI T24E Chassis

I still think they look too bright, too. The Blue and Green guns were turned up way past Red.

Could any damage be done to the heaters if they're left that bright? I can of course change the resistor but I have been turning the set on every so often whilst working on it and making adjustments.

I'll get to prodding about now, unfortunately I don't have a 'scope and have absolutely no idea in how to use one.

Thanks
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Old 3rd Oct 2019, 6:05 pm   #27
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Default Re: RRI T24E Chassis

Short answer is yes. Over-running the heaters is never a good idea and should only be done if the CRT is already on its last legs in order to squeeze a few more miles out of it. trouble is, if the heaters have been over-run, then restoring the correct voltage often results in a dim picture as the cathodes have been stripped by the excessive heat.
Very odd that the set needed a replacement CRT at all (unless broken) and that the engineer fitting it didn't notice the excessive heater voltage, especially as you say he'd changed the feed resistor.
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Old 3rd Oct 2019, 8:51 pm   #28
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Default Re: RRI T24E Chassis

Perhaps it is on it's last legs, and the engineer decided to put as low value he could to squeeze every last bit out of it.

I have no idea how long it's been used like that for, so perhaps it's best to leave it as is?

I wont be using the set much, if at all. I just wanted to fix it on, and perhaps run it for an hour or so, every so often so it isn't left sitting.

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Old 3rd Oct 2019, 9:05 pm   #29
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Default Re: RRI T24E Chassis

If the tube fitted has a 6.3v heater fed from the LOPT, a reading of 4.2v across the heater pins on an AVO 8 set to the AC range will confirm if the heater is being fed correctly and not being over run. J.
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Old 3rd Oct 2019, 9:56 pm   #30
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Default Re: RRI T24E Chassis

Hi

I don't have an Avo 8, I have a DMM instead, should this be able to find the voltage?

Thanks
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Old 4th Oct 2019, 11:00 am   #31
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Default Re: RRI T24E Chassis

Not very likely, unless the DMM will read true RMS values. That's usually reserved for quite expensive instruments.
If you're intending to use it yourself as you say, then I'd just leave it alone and maybe do some fault finding to gain experience.
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Old 4th Oct 2019, 4:04 pm   #32
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Default Re: RRI T24E Chassis

Then I doubt it'd work. It's only a cheap n cheerful one I got online.
I was originally planning to sell it on, but if it's got a poor tube then I doubt it's worth it.

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Old 8th Oct 2019, 1:15 pm   #33
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Default Re: RRI T24E Chassis

As it's been established that the tube heaters are very likely over run the best way is turn the colour down then adjust each control so there is a true black and white screen with no hint of a colour tint on each one. You can then increase the colour so that flesh tones are natural and adjust the contrast and brightness so that is to your liking. You can always find another set
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Old 8th Oct 2019, 8:52 pm   #34
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Default Re: RRI T24E Chassis

I'll remember to do that, when I get a picture on screen.

I did just have a thought although, could it be the tuner, as I get static on screen, but not a picture from a video input?

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Old 9th Oct 2019, 10:53 am   #35
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Default Re: RRI T24E Chassis

Well, it could, but you'd first need to check the 33v feed to the tuning switchbank, and, if it's there, whether the tuner is getting 0-30v on its tuning pin as you adjust the button. Also make sure there is actually an RF signal for it to tune to!
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Old 9th Oct 2019, 1:03 pm   #36
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Default Re: RRI T24E Chassis

Thank you. I'll get round to doing that later. Say there isn't a 33v or 0-30v does that mean the tuner is dead, or could it be repaired?

Thanks for your help
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Old 9th Oct 2019, 4:59 pm   #37
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Default Re: RRI T24E Chassis

Quote:
Originally Posted by Welsh Anorak View Post
Also make sure there is actually an RF signal for it to tune to!
I wondered exactly the same.Check on another receiver that your game/modulator is actually producing one. John.
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Old 9th Oct 2019, 8:51 pm   #38
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Default Re: RRI T24E Chassis

Quote:
Originally Posted by 19Seventy7 View Post
Thank you. I'll get round to doing that later. Say there isn't a 33v or 0-30v does that mean the tuner is dead, or could it be repaired?

Thanks for your help
The 33v is the voltage that is given to the tuner swtchbank from a voltage stabiliser, if thins voltage is missing you cant tune the the set. To select a channel this 33v supply is set to 0-30v by a potmeter or some electronics in the "switchbank". (The preset buttons)
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Old 9th Oct 2019, 8:57 pm   #39
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Default Re: RRI T24E Chassis

Hi,

I have just tested to make sure it's getting a full signal, and it is. It's been on along side a working set, which is displaying a full colour image and sound.

This may sound slightly odd, but when the T24E isn't fully in tune, I get flashes of colour, mainly vivid orange, blue and yellow. Also I see the staticky lines forming a very crude picture which matches on the working sets' screen.

It's a bit of progress, I guess.

Thanks
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Old 10th Oct 2019, 3:30 pm   #40
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Default Re: RRI T24E Chassis

Check the voltage at the VT (tuning pin) varies between 0 and 33v, give or take a volt or two. If so, and the display changes, then it's quite possible you have a faulty tuner. Besides the cabinet and front control panel, that's the bit that wasn't made by Toshiba and, apart from the resistor, is the bit that gave most trouble.
It's a Rank special, I'm afraid, but there are all sorts of options, including making a mechanical tuner work in the place of the original.
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