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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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12th Apr 2018, 12:46 pm | #41 |
Rest in Peace
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Dont forget to ensure that ion trap (mentioned in post #1) is in the original position, if you have moved/removed it during cleaning, when you come to doing your first picture test. If it is out of position, you will not get anything on the screen, as the electron beam will not be directed towards the screen.
If you have left it untouched, it should be Ok. Tony. |
12th Apr 2018, 2:59 pm | #42 |
Dekatron
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Some Pitrie re-gunned CRTs were supplied with a straight gun assembly which did require an ion trap magnet. However, judging by the pictures of your CRT it appears the gun is not a Mazda component and has the look of a Mullard or Philips "bent gun" assembly. If this is the case then the ion trap magnet should be positioned in line with pin three.
DFWB. |
12th Apr 2018, 4:07 pm | #43 |
Dekatron
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
On the subject of test signals, I find that with a screwdriver for an aerial I can hear and see digital stuff (paging?) on my Cossor TV which is fixed on Ch2.
When I got "first light" from the set it was clear from these signals that the RF & IF stages were working well, which gave me a lot of confidence, but it was short lived, and the signals faded out after maybe half an hour. I only got them back after replacing all the Hunts moldseals. It was interesting how they perform their "swansong" before they fail. Is this a well known effect?
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12th Apr 2018, 4:43 pm | #44 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
The ion trap on my tube is pretty much solid and isn't secured by a screw like some others I've seen. It's so tight on there that I'm afraid it will fracture the tube neck if I tried to move it, no idea how they managed to get it on there in the first place. I haven't moved it but if somebody before me has, there's no chance of moving it into the perfect position.
So what's the deal with the EHT valve that won't light? Is it AC or DC current flowing through the booster capacitor? Peter |
12th Apr 2018, 6:15 pm | #45 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Hi Peter,
The boost cap C98 (not C90 as I said before) has a fairly high DC rating. 1000V would be ideal but anything over 600V should be fine, at least for testing. I doubt if the one you've fitted has failed already unless it's a very low voltage rating. One side of the cap is connected to the HT rail, the other to the transformer. It's the transformer side which will develop the 'boost' volts. In this case 410V. It will only do this if the line stage is working correctly. First thing to check is the main HT rail. This should be about 195V or so. The metal rectifier, MR2 could be suspect if its low. You can measure this on fuse F3 which feeds the line O/P stage. Check it's present on both sides of the fuse! C97 (60pf) and C94 (150pf) need to be high voltage types 4KV or so. If you have changed them, are they suitable? Unfortunately, there is only one combination of events which will allow the whole line O/P stage to function correctly:- there are any number of reasons why it won't operate! You just have to work through things systematically to find where the fault or faults are. All the best Nick |
12th Apr 2018, 7:13 pm | #46 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Ah ha! you may have possibly pointed out a few of the causes there. First off I replaced C98 which I read on the cap as 0.5uf 350V with a 0.47uf 400V cap.
Next, I have not replaced C97 or C94. And finally I forgot to mention that while kneeling down trying to squeeze the chassis beck into the cabinet, the carbon rod on the HT line which I believe is called a metrosil, right? slowly worked it's way out of the protective plastic tube and right under my knee. Long story short it snapped in 2 but I managed to seamlessly repair it with superglue. However by the looks of it this is not the first time it has happened because further up the rod there is some messily applied epoxy and a metal clip. Peter |
12th Apr 2018, 7:21 pm | #47 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Dont worry about the metrosil. Just leave it out.
No glue will work properly.
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12th Apr 2018, 7:35 pm | #48 | ||
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Quote:
Quote:
No harm leaving the set on to 'cook' (not literally)! I wouldn't leave it unattended though.
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12th Apr 2018, 8:29 pm | #49 | |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Quote:
Not sure why either I've just heard from a few people that it's the case haha |
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12th Apr 2018, 8:37 pm | #50 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Getting about 220VDC both sides of the fuse
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12th Apr 2018, 8:44 pm | #51 | |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Quote:
Seriously though, you will need to find a way to get the chassis into a stable upright position whilst still connected to the tube. You need to get to the underside to make measurements etc. and most of those will need to be done with the thing powered up You don't want the chassis to fall over when it's powered! I seem to remember that due to the cabinet design, that wasn't that easy! You might have to make some wooden supports. The U26 heater is as bright as any other valve so its very obvious if its alight or not. The glow is reflected off the shiny metalwork inside the valve which makes it easy to see. Don't be tempted to leave it running for too long until you are sure that the line stage is working correctly. Things can get way too hot in a short time if there is a fault. Cheers Nick |
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12th Apr 2018, 9:14 pm | #52 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Good. Assuming that the mains dropper is set to the correct voltage tapping, that implies that the line stage may not be taking much current as the HT is high.
My next suggestion would be to measure the boost voltage. This will confirm several things. At switch on it should be zero as the boost diode (V15) will be cold. As this warms up, the boost volts will rise to the HT volts. If the line stage works, then the boost will increase to 400 odd volts as the line O/P valve warms up. If the line stage is not working, the boost will stay at the HT voltage. If the voltage starts at zero and then rises to the HT voltage as V15 warms up, it implies that V15 is OK. If the boost rises instantly at switch on to HT voltage, it implies a shorted boost cap. A 400V cap is a bit marginal but will probably be OK for testing. You then need to measure the screen and grid volts on the 30P4 LOP valve. Don't try to measure the top cap of either valve:- your meter won't like it The grid should be negative by 40 volts or so. The screen should be 105V Interestingly, it has a 22R resistor in the cathode. Check that's OK. The cathode voltage is shown as 2.2V All the best Nick |
12th Apr 2018, 9:29 pm | #53 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
I guess the easiest way to have the chassis working outside the cabinet is to remove the chassis, turn the cabinet on its side and have the chassis on its side as well perhaps the wires coming to and from the tube can reach far enough. I'm busy all day tomorrow so it can be a 'pleasant' saturday morning affair
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16th Apr 2018, 7:34 pm | #54 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
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16th Apr 2018, 9:24 pm | #55 |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Hi Peter,
First you need to locate the boost cap. It's shown as C98 on my circuit, but may be different on yours. It's shown as being clipped to the chassis just under the hole under the LOPT. One side of it is connected to the HT rail. The other side is connected to the LOPT, the width control, C97 and the scan coil plug. It's this side which is the 'boost' line and the voltage on it should behave as I indicated above. Cheers Nick |
17th Apr 2018, 5:34 pm | #56 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Ni Nick
I measured the boost voltage although I'm unsure whether I should be measuring AC or DC. From cold, the DC reading immediately goes up to around 320VDC and stays there. When I measured AC from cold, the voltage immediately shot up to around 720V and remained there for about 10-15 seconds until it began to fall and stabilise at around 520VAC. https://youtu.be/asKAcMnC3EA Also have you noticed the time it takes from switching on to hearing the flyback transformer, Is it normally this long? |
17th Apr 2018, 8:42 pm | #57 | |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Quote:
I like your YouTube video- very good idea! You should be measuring with the meter set to DC. As you get 300 odd volts at switch on, I would suggest you are measuring the wrong side of the boost cap! I think you are measuring the side that goes to the HT rail. Try the other side of the cap. The 'boost' side of the cap, connected to the LOPT, gets it's voltage via the efficiency diode V15. At switch on you should get no voltage until V15 has warmed up. If you get voltage at switch on on both sides of the cap, there is a problem somewhere! Warm up time is usually a good minute or more until you hear the line whistle. If the line stage is working properly, it should be loud and irritating! Your's sounds too feeble to me. Cheers Nick |
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17th Apr 2018, 9:55 pm | #58 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Hi Nick, yes I was measuring the wrong end of the cap, I double checked it visually before measuring and could have sworn I had it on the correct end haha!
The LOPT whistle is a lot more prevalent in person than the camera makes it out to be. See below the readings I got for the 30P4 valve, I have no idea why it has rotated the pictures like that Peter |
17th Apr 2018, 10:15 pm | #59 | |
Octode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Quote:
The screen volts on the 30P4 are too high and coupled with the slightly low cathode voltage, would indicate that the valve is not drawing enough current. This could be due to a low emission valve or incorrect drive amongst other things. What are the anode & cathode voltages on the line oscillator valve V18A? Have you tried another 30P4? Cheers Nick |
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17th Apr 2018, 11:07 pm | #60 |
Hexode
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Re: First TV Project - Ekco TCG316 - Any Advice Appreciated
Oh sorry, boost voltage rises from 0 to 280V when the valves warm up as it should.
V18A Cathode = 0.35V V18A Anode = 155V I don't have a spare 30P4 currently but I can get one ordered Thanks |