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Old 19th Jan 2022, 9:58 pm   #61
Panrock
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Default Re: Another TV22

Have you a valve tester?

Steve
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Old 19th Jan 2022, 10:13 pm   #62
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Default Re: Another TV22

I do have access to an AVO VCM, I did test all of the EF80s and most were good, three I replaced with some from my spares which are also tested and good. The only ones I haven't tested are the EB91s but I should have some spares to try.
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Old 19th Jan 2022, 10:18 pm   #63
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Default Re: Another TV22

Hi.
The fact its snowy makes me think the gain is OK and it's down to a bad connection or an issue "before" the RF amp and not necessarily valve related. I know if the F connector going into the standards converter has the cable partially removed from the plug when turning up the contrast on the set, the picture gets snowy. If the set has genuinely low gain it cant get snowy.
Check the coils before the RF amp, caps and connections, also check the screen on the coax is actually earthed and there is no outer braid shorting to the inner, one fine wire is enough, If you are using a modern distribution box for an aerial system remember they are not designed for band 1 and can attenuate the signal.
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Old 19th Jan 2022, 10:25 pm   #64
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Default Re: Another TV22

You could also try running the set in its cabinet upside down and then tapping the upturned base. This might reveal a broken core. Just a thought.

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Old 19th Jan 2022, 10:28 pm   #65
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Default Re: Another TV22

Hi.
If you have an isolating transformer then try this, if you don't then I advise you not to try this.
Disconnect the aerial input from the TV, Ground the braid of the Coax to the RF chassis metalwork, connect a 22 or 47pf cap to the center of coax and on the other end of the cap connect it to Pin 2 of the RF amp EF80 and see what it does. It may look off tune but see if the level of signal goes up, high contrast on these sets directly fed from the aurora or hedghog should invert the picture.
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Old 20th Jan 2022, 2:16 pm   #66
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Default Re: Another TV22

Thanks Steve and Trevor for your help and suggestions. I will try Steve's suggestion of tapping with the set upside down and seeing if anything changes, as there were one broken core and others messed with it wouldn't surprise me if more damage exists hidden away.

Trevor, I have tried your suggestion and found a 30pF cap in my tins of odd bits, connected to pin 2 of the RF amplifier and then connected the co-ax with shielding to RF chassis. Attached are the results, signal is a bit off tune but it doesn't seem to do make any difference to the contrast at all, the control still needs to be fully clockwise and the level looks about the same as when the signal is going through the aerial input.
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Old 20th Jan 2022, 3:51 pm   #67
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Default Re: Another TV22

Forgive me if you've already done this, but can I assume you've already run a meter along all the relevant anodes and screen grids on the deck, to check for volts where there should be and open-circuits?

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Last edited by Panrock; 20th Jan 2022 at 3:55 pm. Reason: clarity
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Old 20th Jan 2022, 5:14 pm   #68
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Hi Steve,
I have just re-checked this as I did some measuring prior to Christmas. I have noticed that V2 (Oscillator and Mixer) EF80 isn't quite right with the service info, the Anode voltage is 151v and Screen is 181v the service data suggests it should have 150v on the Anode and 60v on the Screen. The resistors didn't seem awfully out of spec but I suppose with them being on the HT line they may have more of an effect, I'll focus my attention around here first and see how things improve.
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Old 20th Jan 2022, 6:38 pm   #69
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Default Re: Another TV22

The V2 screen grid acts here as the oscillator 'anode'. Measuring its 'DC voltage' as seen on a meter could be something of a black art. One might now do well to take a look at the oscillator waveform and check it for a clean, pure waveform and correct frequency... A loop on the end of a (VHF-capable) scope probe is indicated to have a look. And examine closely the state of L4 and L5 and C6 (service sheet 1091). How good really is that new core I believe you attached, I wonder?

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Old 20th Jan 2022, 9:09 pm   #70
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Thanks for the suggestions Steve, I may have some difficulty scoping the osc. waveform as it may be a little beyond the reach of my scope and probes. I have considered myself whether the new core is up to the job. The originals seem to be somewhat more dense and weighty than the new type I have fitted, but that is all that I could find and so I was left with little choice. I could try swapping the cores over on L2/L3 (this has the original fitted) and L4 (this has the replacement core fitted) and see if that makes any difference.
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Old 20th Jan 2022, 10:54 pm   #71
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Default Re: Another TV22

Going back a bit. Did you reinstate the wiring when you removed the Band 3 tuner? J.
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Old 20th Jan 2022, 11:25 pm   #72
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Default Re: Another TV22

Hi John, yes I'm sure I did it all correctly. I recall it being a wire from the contrast control to a 220 Ohm resistor on V3 if memory serves me right.

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Old 21st Jan 2022, 10:45 am   #73
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Default Re: Another TV22

Hi.
Thanks for injecting the signal into the RF Amp, via pin 2. This has proven the RF coils are OK. As has previously been stated measuring the DC voltage on the oscillator screen is basically a no no with a meter, the meter leads and cables will damp the oscillator and change the DC conditions. I think the oscillator is miles off, perhaps its the 100pf feedback cap on V2 it's fairly common fault which I've had, they often read OK but break down in circuit
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Old 21st Jan 2022, 1:05 pm   #74
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Hi Trevor, I'll see if I have a suitable replacement for the 100pF, funnily enough I don't know if you mentioned it earlier or if I read in another thread about this cap being problematic. Let's hope it offers some improvement.
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Old 21st Jan 2022, 2:07 pm   #75
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Well a quick rummage through some spares and I found an old 100pF mica capacitor, fitting to the set offers virtually no improvement and still the same problems. Now, I also noticed when no signal is applied and the brightness turned up there looks to be a black modulation travelling upwards on the screen, I'll try and make a video and link it in to the thread. Whether this is related to the problem I'm having I'm yet unsure.

I will order a new 100pF capacitor just to eliminate any possibility of these old ones having any problems.
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Old 21st Jan 2022, 9:58 pm   #76
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Default Re: Another TV22

If another cap gives exactly the same result I think you can discount it. If you have a 40mhz scope you should be able to trace the signal all the way from the aerial input.
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Old 21st Jan 2022, 10:19 pm   #77
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Hi.
Things to check and do are these: check R1, R2 & R9. Does the contrast control work? Check C3, C4. Also check there is a low resistance between connection 1 & 2 on L4 and do the same on L5 between 2 & 6. Check for a low resistance between G1, pin 2 of V1 to chassis.
If all this passes then I'd say the RF section is OK up to the mixer V2. A simple check is also the coax to the Aurora and TV aerial input, no shorts or open circuits, the center of the coax to protrude 5mm above the F connector so its inserted prior to the body of the plug getting screwed in.
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Last edited by murphyv310; 21st Jan 2022 at 10:25 pm.
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Old 22nd Jan 2022, 12:23 am   #78
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Default Re: Another TV22

Hi Trevor,

Thanks for the above suggestions, I can confirm R1, 2 and 9 are all okay. C3 & 4 also meter okay when testing for any shorts but I may just change these to help eliminate them, the contrast control is also okay. All coils have been checked before and are okay. I did finally just replace the valve base of V4 as I was still having connection issues, the replacement valve base now gives perfect contact so that's one issue out of the way.
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Old 22nd Jan 2022, 10:38 am   #79
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Default Re: Another TV22

From your pictures [turn the flash off!] it appears to be pre oscillator, in the RF stage.
The excellent self contained band 3 tuner is a complete Band 3 unit. If you reconnect this and reset your standards converter for a channel in Band 3, you can eliminate the Band 1 front end completely.
Check your aerial connection lead for continuity. You should be able to overload the front end with the contrast backed off. A very serious lack of gain here that will turn out to be a simple answer. J.
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Old 22nd Jan 2022, 10:51 am   #80
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Default Re: Another TV22

PS
I took this picture a few moments ago on one of the TV22s in my collection. Signal from Aurora with 18db attenuator, contrast 3/4 advanced. The Hedgehog gives similar excellent results. This should give you some idea what is to be expected gain wise. This example has not been turned on for a considerable period hence the slight readjustment required but it's too cold to fiddle with it! John
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