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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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2nd Sep 2007, 2:17 pm | #1 |
Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
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TV24 - no picture
After a marathon recapping session yesterday I finally plugged in at about 4.30am.
All seems well except there is no picture, I do have: - all valves including EY51 glowing - line whistle - a 50ish hertz buzz from the field coils - life from the CRT heater - set left on for 5 minutes and no smoke or glowing plate - a telling off girlfriend I've tried touching a grounded screwdriver to the EHT CRT cap and no spark after set is switched off - do I have a duff LOPT? How do I test / where should I look first? Cheers Dom |
2nd Sep 2007, 2:28 pm | #2 |
Dekatron
Join Date: Sep 2003
Location: Bolton, Greater Manchester, UK.
Posts: 6,644
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Re: TV24 - no picture
What's your Girlfriend telling you off for? You've done nothing wrong!
Anyway, The EY51 could be faulty or dry jointed. The lead to the EHT cap on the tube could be faulty. The connection to the EY51 Anode could not be there. Is the Brightness Control OK. The Ion Trap could be out of place. (Magnet on tube neck. See if it's loose!) The A1 could be absent. Metrosil and C31. Also, if you've been up that late, in the cold light of day check everything again!! Cheers, Steve P
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If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...? |
2nd Sep 2007, 4:08 pm | #3 | |
Octode
Join Date: Oct 2003
Location: Newbury, Berkshire, UK.
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Re: TV24 - no picture
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Chris |
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2nd Sep 2007, 4:44 pm | #4 |
Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
Posts: 1,885
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Re: TV24 - no picture
What are my options for testing the EHT?
When checking by trying to get a spark is it safe to do this with the set on, or does this run the risk of burning out the lopt? Is the fact I'm not getting a spark due to the fact that I've switched off and its discharged? Wiring round the EY51 should be ok - I had to resolder it after a leg dropped off but I'll check again I have AVO8 or reasonable digital multimeter - neither go as high as 8kv - is it safe to make a chain of 1M resistors as a potential divider? Cheers Dom |
2nd Sep 2007, 4:53 pm | #5 |
Octode
Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,323
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Re: TV24 - no picture
If the EY51 is glowing and you have line whistle, there is a good chance you have EHT. Have you checked the 2uF cap (C32 on Trader sheet 1-91/T38) in the middle of the tag board under the main chassis? I’d change all the electrolytic caps too anyway with the possible exception of the large main smoothing cap, unless it is faulty.
Have you cleaned with meths or similar all around the tube EHT connection? If this is VERY grubby, it's possible some of the EHT is leaking across to earth. Have you moved the tube and/or focusing magnets? If the gun in the tube looks a bit angled, there should be a small magnet on a clamp between the tube neck and focusing magnets. Have you inadvertently moved this? On my TV22, there’s between 0 and 100 volts on the centre of the brightness control depending on setting, about 300 volts on the tube side of the metrosil and about 500 on the other side of the metrosil. If you are brave, (I wouldn’t recommend it!) experienced hands would draw a spark from the EHT tube connection using the screwdriver blade of a very thick, well insulted handled screwdriver. Spark should be almost invisible, but about 1cm long if all is more-or-less ok. Ian Reading Last edited by Ian - G4JQT; 2nd Sep 2007 at 4:59 pm. |
2nd Sep 2007, 5:06 pm | #6 | |
Octode
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Location: Newbury, Berkshire, UK.
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Re: TV24 - no picture
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Chris |
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2nd Sep 2007, 5:53 pm | #7 |
Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
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Re: TV24 - no picture
Mmm no spark when on either, got a very dirty curved triangle wave at the grid of v8 (line driver) - is this normal no signal behaviour?
G1 ~ 100V G2 ~ 220V K ~ 120V Will test v8 and ey51 on a characteristic meter and report back later. Dom |
2nd Sep 2007, 11:46 pm | #8 |
Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
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Re: TV24 - no picture
I've checked the PL81 (involved repairing my flood damaged AVO Char. meter!), its just shy of 100%.
I happened to have an EY51 in a box of lucky dip valves I got years ago! Well worth the ten quid! I've now go a big fat spark at the EY51 anode (to the side of the shielding tin until a bit of resoldering) and a 1/2 inch spark at the EHT cap. Still no picture I've tried fiddling with the ion trap - no joy Measured the following voltages at the tube at max brightness: k: 128V g1: 111V g2: 260V At min. brightness k: 120V g1: 0V g2: 267V These look a bit suss to me. I would have expected cathode to rise as more current is drawn but I'm pretty ignorant when it comes to CRTs Also the magnet in the ion trap is a bit feeble, it attracts a screwdriver tip fairly weakly, is that likely to be a problem. The magnet appears to be a sort of torroid affair around a bolt. Is there a particular orientation of this magnet? What do i do with the ion trap, I've tried sliding it back and forth and round and round to no avail. Slightly frustrated, but enjoying it really! I really hope I can get it going for next week - I'd love to watch the Grand Prix on it though I'm not sure the girlfriend will approve of the line whistle! Cheers Dom |
2nd Sep 2007, 11:54 pm | #9 | ||||
Octode
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Location: Hebden Bridge, West Yorkshire, UK.
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Re: TV24 - no picture
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Cheers Dom |
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3rd Sep 2007, 7:56 am | #10 | |
Dekatron
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
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Re: TV24 - no picture
Dom
Quote:
OK to earth the cap on the CRT, though, with or without disconnecting the lead.
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3rd Sep 2007, 9:06 am | #11 |
Octode
Join Date: Nov 2004
Location: Hebden Bridge, West Yorkshire, UK.
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Re: TV24 - no picture
Cheers Mike,
It wasn't deliberate I've got an aversion to sparks in general! It was just arcing over by itself because there was a (very small) solder spike. I'm a bit dubious of the design of the shielding tin in that area though - it seems a bit close to the lopt for comfort! Any ideas about the ion trap / no picture problem? Cheers Dom |