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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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20th Nov 2021, 6:08 pm | #21 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Just providing an evening update here, I've carefully followed all of the circuit of the timebase section and compared with the schematic, all is okay, values of resistors and capacitors seem to be good, no shorts either. The frame linearity and height controls are also good aswell as the frame hold control.
I've made a short video showing the frame collapse, as can bee seen in the video it looks as though it is attempting to scan down but something is killing it off. I'd have thought such a fault would be capacitor related but all have been replaced in this area and the circuit is all as of should be. https://youtu.be/Xzv_zRMpfNA |
20th Nov 2021, 6:19 pm | #22 |
Heptode
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
Posts: 988
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Re: Another TV22
Hi EF80TVVALVE ,
Have you checked the resistance of the frame blocking oscillator transformer? It is located on one of the side tag boards and they often fail with an O/C winding. Cheers Andy
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20th Nov 2021, 6:38 pm | #23 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
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Re: Another TV22
Hi Andy,
Yes, the transformer measures fine DC resistance wise very close to the Bush service data. I've checked all of the circuitry around the ECL80 and I'm absolutely stumped as it checks out fine! Cheers Bren |
20th Nov 2021, 7:07 pm | #24 |
Heptode
Join Date: Jun 2006
Location: Ware, Hertfordshire, UK.
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Re: Another TV22
Hi Bren,
As you have replaced the burnt tag board then you must have had the blocking oscillator transformer transformer out. Are the leads connected in the correct order? If on of the windings is the wrong way round then that would stop it oscillating. Cheers Andy
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20th Nov 2021, 7:12 pm | #25 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Hi Andy,
Yes that's right, it was swapped over when the board was replaced. It is connected correctly, the primary and secondary are on the correct sides of the valve and connected as they should be. In fact, I have checked all the wiring from the replaced board and its components and I can safely say 100% that everything is fine in that area. The circuit matches up spot on with the schematic which is why ai've begin to hit a brick wall. Cheers Bren |
20th Nov 2021, 10:24 pm | #26 | |
Hexode
Join Date: Sep 2019
Location: Crystal Palace, Bromley, London, UK.
Posts: 417
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Re: Another TV22
Quote:
You mentioned that you cleaned the valve contacts. I have had similar issues (frame collapse) which were solved by some valve wiggling (ECL80). I imagine you've done this already, though. Helder |
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20th Nov 2021, 10:56 pm | #27 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Hi Helder,
Yes, at the start of my desperacy I checked the valve holders for continuity and gave them a clean too, I'm now confident that they are okay. I can confirm that the flashing with the frame collapse is indeed a frame scan, I briefly turned up the brightness and in focusing the beam I can see the line structure and some flyback lines within the flash, so it seems every second or so something is happening that is causing the frame to collapse. |
20th Nov 2021, 11:24 pm | #28 |
Dekatron
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
Posts: 5,420
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Re: Another TV22
Have you looked at the blocking oscillator waveforms (if any) on the scope?
You need to ascertain if it's an oscillator issue or output. One thing that comes to mind is a partial short to ground on one of the frame controls (hold, height or linearity) or shorting rubber wiring.
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20th Nov 2021, 11:34 pm | #29 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Not yet Trevor, my scope is currently at the back of a cupboard but I'll attempt to dig it out tomorrow and scope it at various points and see what's going on. Hopefully that will narrow things down a bit, it's turning into a real head scratcher.
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21st Nov 2021, 5:21 pm | #30 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Today I've scoped both sides of the blocking transformer, I've photographed the outputs although it's very difficult as my scope doesn't have a very long persistace phosphor, so my camera was set to 1s shutter speed. The sheer drop in amplitude is when the flicker of frame scan appears. I'd have expected it to be running much faster than it was, the images were taken at 0.1 & 0.2 secs on my scope. I'm going to carry on searching but should I now focus my attention to V7 ECL80, the output of which goes to the westector? With that also said what symptoms would a faulty westector give?
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21st Nov 2021, 8:20 pm | #31 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Hi all,
So more investigation has lead to a 'tick' that I can hear in time with the flash on the screen. I've located it to be in the vicinity of the timebase board on the side and possibly the transformer itself although I'm going to investigate a little more first. I did note that the DC resistances were fine but it may be possible that there is some insulation break down when working at operating voltages. I will have to see if I can find some sort of replacement transformer to fit and test this theory, but I'm not too sure I have anything suitable. |
21st Nov 2021, 8:39 pm | #32 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,171
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Re: Another TV22
Hi Bren, most blocking osc transformers should do, the Bush one has a ratio of 3:2
Ed |
21st Nov 2021, 9:10 pm | #33 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Thanks Ed, I'll see what I can find. As long as it proves the current one is faulty then that's all I need, I can then get it rewound.
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21st Nov 2021, 10:13 pm | #34 |
Dekatron
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Location: Kilmarnock, Ayrshire, UK.
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Re: Another TV22
What was the time base set to and the amplitude. Was the waveform in the first photo consistent. Did you look at the anode of the pentode section of the ECL80 Frame output?
A few questions but a methodical approach is very important. A scope is far more informative than a DVM, One piece of test equipment that will give the most info and leads when fault finding. Surprisingly many rarely use their scopes.
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21st Nov 2021, 10:48 pm | #35 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
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Re: Another TV22
Hi Trevor,
Thanks for your help, I've attached some photos for you. I must admit I mostly use scopes on audio amplifiers and my waveform knowledge of televisions isn't great, something I should really learn more. I'm currently looking at some other service info to see what sort of waveforms I should be expecting at various points. Photo 1: 5v/cm TB: 0.1sec Anode ECL80 at frame blocking tx Photo 2: 2v/cm TB: 20ms As above, this is modulating the photo 1 waveform Photo 3: 20v/cm TB: 10ms Blocking TX output to height control Photo 4: 0.5v/cm TB: 10ms As above, this is modulating photo 3 waveform |
21st Nov 2021, 10:56 pm | #36 | |
Dekatron
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
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Re: Another TV22
Quote:
As Ed correctly states virtually any frame blocking oscillator transformer will work irrespective of the different DC ohms values. The only problem you have is if its an unknown one you may not get it wired correctly and there are a few combinations before getting a result. Just make sure the resistors R4, 5, 6 & 8 are OK and there are no leaks in the pots I've already mentioned, I had a short to chassis in a vertical hold pot about 18 years ago on a TV24.
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21st Nov 2021, 11:06 pm | #37 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
Posts: 1,431
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Re: Another TV22
Thanks Trevor,
I do know R4, the 680k is high, measuring 900k, the others are a little off but not as bad as that. I will swap these tomorrow but I have a 680k on order as I don't have any replacements here. We'll see if swapping these makes any improvement. The pots are definitely in good order with no shorts, they were scratchy so I've cleaned them and can confirm that they are in very good order. |
22nd Nov 2021, 6:17 pm | #38 |
Dekatron
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Location: Kilmarnock, Ayrshire, UK.
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Re: Another TV22
Thanks for the waveforms Bren.
Could you look at the anode of the ECL80 pentode frame output. Remember to reduce the sensitivity of the scope as the level there will be much higher....or should be!
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22nd Nov 2021, 9:14 pm | #39 |
Octode
Join Date: Feb 2010
Location: Leicester, UK.
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Re: Another TV22
Hi Trevor,
Well after some searching I've actually found the fault, a simple thing but we all do it on occasion. I was checking the dissapation of the 680k as I had a 2w to spare that I was going to rig in for the time being. It's then I realised that there was no voltage across it and although the red wire went to the HT tag of the scan coil tx the wire had snapped, hanging on only by the insulation. Presumably using a DMM wasn't helping as I did note the HT was varying on the ECL80, should I have used my AVO 7 I'd have probably realised this earlier. So, I now have a nice full raster with good focus and linearity. The next problem is getting signal through the RF deck. I mentioned earlier that the iron dust cores of one coil had snapped and mostly dissapeard, I think this will need replacing so I'm going to post a wanted thread in hopes that somebody has one spare. It does have a band III converter fitted and ideally I'd like to remove it, it's no longer of any use and the condition is very poor. I usually like to keep things like this in situ as part of the sets history but I'd rather this be removed as it hasn't survived well over the years. |
22nd Nov 2021, 9:55 pm | #40 |
Dekatron
Join Date: Sep 2006
Location: Kilmarnock, Ayrshire, UK.
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Re: Another TV22
Good stuff.
Often the simplest of issues cause so much head scratching. Well done
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