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Old 16th Sep 2019, 10:39 am   #41
peter_scott
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Default Re: Yet Another Bush TV22

Hi David,

I already had a degaussing coil from my poor edge focus experiments on the HMV901. I just placed the scan coils on the carpet with the degausser surrounding them, then applied power and slowly lifted the coil upwards and away.

Peter
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Old 16th Sep 2019, 10:50 am   #42
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Default Re: Yet Another Bush TV22

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Originally Posted by beery View Post
Now I know from its circuit position, C63 should not effect the frame timebase, it is worth checking anyway as I usually find it to be low in value, which is a surprise as the dual canned C61 and C62 are usually fine.
In my set the C61/62 capacitor was a little low in value and leaky. So I removed the base, while largely preserving the aluminium canister, discarded that and the old contents. Not a pretty sight in there in these old capacitors, I wouldn't trust a vintage electro to be reliable here. The more of these I open up, the more horrified I become. It is worth rebuilding to avoid trouble.

I machined a new thicker base made of 1/4" thick insulating material and created 3 lug connections using nickel plated brass 3mm screws, and have solder lugs on those both inside & outside the canister.

To identify the terminals I drilled superficially into the surface of the insulator near the screws/nuts and applied three dots of enamel paint, red, yellow and black for the common(two of these are just visible in the photo). I fitted the new base into the canister with a small amount of non-acid cure silicone rubber. So with enough force the base can still be extracted one day, to replace the electrolytics. One day it will have to be done again in a decade or few...these are electrolytics, it is inevitable.

If I had been able to fit a polyester or polypropylene in there of a higher voltage rating and same uF value I would have, to avoid future failure, but in this case due to the combination of uF value and voltage, I could not do that and was forced into using the electrolytics. I used the best quality ones I could find.
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Old 16th Sep 2019, 11:32 am   #43
peter_scott
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Default Re: Yet Another Bush TV22

I would like to do something similar to that Hugo but I confess that currently I just have my modern electrolytics just hanging on their wires.

The frame timebase does appear to have quite a few high impedance nodes so I suppose I shouldn't be surprised that 50 Hz mains can get in where it's not wanted. Just touching my 1M scope probe on any of the oscillator transformer connections gives a substantial increase in scan amplitude.

With the hum bucking C60 in place the HT ripple is 1 volts p-p. With it disconnected the ripple is 3 volts p-p but with or without C60 the apparent amplitude of the frame ripple doesn't appear to change!

Peter

Last edited by peter_scott; 16th Sep 2019 at 11:49 am.
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Old 16th Sep 2019, 12:13 pm   #44
FERNSEH
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Default Re: Yet Another Bush TV22

Peter_Scott wrote: "I already had a degaussing coil from my poor edge focus experiments on the HMV901. I just placed the scan coils on the carpet with the degausser surrounding them, then applied power and slowly lifted the coil upwards and away."

Hi Peter,
that's a much more gentlemanly approach to doing the job. Mine certainly wasn't

DFWB.
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Old 16th Sep 2019, 12:20 pm   #45
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Default Re: Yet Another Bush TV22

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With the hum bucking C60 in place the HT ripple is 1 volts p-p. With it disconnected the ripple is 3 volts p-p but with or without C60 the apparent amplitude of the frame ripple doesn't appear to change!

Peter
That does suggest the hum is not getting to the frame circuitry via the HT rail. So most likely then, heater-cathode leakage, which any amount of is much more of a dilemma in series heater chain designs, as you move along the heater chain away from the chassis end.
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Old 16th Sep 2019, 12:26 pm   #46
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Default Re: Yet Another Bush TV22

It doesn't appear to be a valve fault because half a dozen different ECL80s all display the same frame ripple and the cathodes are at ground potential. I did push the heater wires about this morning and did achieve a quieter sound intrinsic but have yet to see any frame improvement.

Peter
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Old 16th Sep 2019, 12:45 pm   #47
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Default Re: Yet Another Bush TV22

Just a thought, could this just be some sort of external interference, either on the mains or otherwise? I had a problem a while ago where a set I was working on displayed all the symptoms of a dying smoother, but it was intermittent, it would have the picture snaking around then just suddenly stop and be rock solid! It was quite annoying, but then I decided the TV itself wasn’t to blame when I had several sets running together and they all displayed the same picture snaking, and the real give away was when it stopped suddenly on all the sets at the same time! The only sets that didn’t show it were the more modern sets from the 70’s onwards, and I never did get to the bottom of it, just had to live with it!

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Old 16th Sep 2019, 12:53 pm   #48
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Default Re: Yet Another Bush TV22

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It doesn't appear to be a valve fault because half a dozen different ECL80s all display the same frame ripple and the cathodes are at ground potential. I did push the heater wires about this morning and did achieve a quieter sound intrinsic but have yet to see any frame improvement.

Peter
Its been a while since I looked at the schematic and yes not likely heater-cathode leakage in this case.

Of course the frame amplifier has a good response at mains frequencies and the resistances are high, so the wiring leading to the Hold,Height and LIN controls could easily pick up signals from other nearby wiring, like the heater wiring.
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Old 16th Sep 2019, 1:16 pm   #49
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Default Re: Yet Another Bush TV22

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Just a thought, could this just be some sort of external interference.
Regards
Lloyd
That's an interesting thought. The set is being run from an isolating transformer but that is 5' away but I am also feeding the transformer from a variac just beside the set so with anticipation I removed and disconnected the variac from the mains switched off my scope and soldering iron but alas no improvement and there's nothing else that could be generating a stray field.

Thanks for the thought though.

Peter
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Old 16th Sep 2019, 1:33 pm   #50
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Default Re: Yet Another Bush TV22

Hi Peter,

Just to be clear, do you still see this frame ripple on an unmodulated raster, with no aerial connection? And with a different signal source connected, say a Sig Gen playing tone?

Steve
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Old 16th Sep 2019, 1:34 pm   #51
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Default Re: Yet Another Bush TV22

There could be some interesting possibilities.

Looking at the video of it, it suggests the ripple is amplitude modulating the drive voltage coming out of the vertical oscillator. Probably you have already checked C59 (on trader sheet 1091/T38) that bypasses the blocking osc transformer primary from the supply with R56 a 220k. Also probably worth checking the grid resistor on G1 of the pentode part of the ECL80, even if this was nearly open circuit, the stage would still appear to work. And that C57 is not leaky.

Does your set have the original blocking osc transformer and is it mounted with the same orientation as the original ?

(Steve...as the ripple rolls through it looks like it affects both the vertical scan linearity and height, so it must be in the raster)

Last edited by Argus25; 16th Sep 2019 at 1:41 pm.
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Old 16th Sep 2019, 1:59 pm   #52
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Default Re: Yet Another Bush TV22

A couple of thoughts. Could the heater isolation transformer be causing a stray field?

Add a rectifier and smoother to the heater chain to run it from smooth DC. You would have to add extra resistance to the heater chain to allow for the cap charging up to peak voltage.

Al
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Old 16th Sep 2019, 2:11 pm   #53
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Default Re: Yet Another Bush TV22

I do take your point Hugo. Though surprising effects can sometimes happen... worth ruling them out. Are we sure the Isolation Transformer is not leaky? Nor the mains wallwart (?) feeding the Aurora if used (?) Is the chassis currently 'earthed'? How? Does the ripple remain with the set connected directly to the mains and with no aerial connection? (I agree that it should).

Steve
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Old 16th Sep 2019, 2:30 pm   #54
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Default Re: Yet Another Bush TV22

Peter,

My TV22E (or F?) is a bit different from the TV22, being 625 lines, but I had a similar hum modulation problem.
Probing seems to point at the grid (pin 9) of V3 (ECL80), around where the unwanted hum appeared to get in.
Just hold a screwdriver to that pin and verify the hum gets worse - then you have the same problem.
As a (not-to-elegant) solution I disconnected R12-C12-R23-C19-R24 on top of the chassis, and replicated this circuit below deck.
This reduced the hum substantially.

Hope this helps a bit.

Jac
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Old 16th Sep 2019, 2:52 pm   #55
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Default Re: Yet Another Bush TV22

Stop the frame oscillator working and note if there any deflection of the thin white line.

DFWB.
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Old 16th Sep 2019, 2:59 pm   #56
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Default Re: Yet Another Bush TV22

Very many thanks for all your thoughts. I haven't pursued them all yet but I think I have eliminated faulty or wrong value components around the frame oscillator.

Looking at waveforms wrt ground I can't see any movement in the frame output drive or anode but if I look on the secondary of the output transformer then (wrt ground) the wiggles are clear to see. The osc. transformer is original and I don't think it has ever been removed since manufacture.

I did try removing the C34 2uF electrolytic mounted on the scan coils but this made no difference to the wiggles. It appears to simply straighten the top lines of the scan when in circuit.

Disconnecting the signal the timebase free runs and appears to still be interacting with the interfering mains.

I did wonder if the HKS transformer could be affecting the frame ECL80 that it is mounted next to so I put an aluminium sheet between the two but couldn't see any change.

I don't think the HKS could be leaky because primary and secondary are side by side in separate partitions of the plastic former.

Yes Jac, holding my finger on the grid of the output valve does give an accentuated version of the fault.

Shorting the triode grid to ground I can't really see any wiggles.

Thanks to all,

Peter

Last edited by peter_scott; 16th Sep 2019 at 3:07 pm.
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Old 16th Sep 2019, 4:28 pm   #57
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Default Re: Yet Another Bush TV22

Oh dear! I think I may have got you all searching for a solution for nothing. Sorry.

I just decided to look at the thing with the RF deck screwed in. It's not perfect but miles better than it was.

I did have a crock clip lead coupling the RF to the main but possibly not good enough.

See: https://youtu.be/xXBL6R4ILLA

Peter

p.s. I don't believe it! It's failing again. Perhaps the mains was just in synch.

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Old 16th Sep 2019, 5:19 pm   #58
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Default Re: Yet Another Bush TV22

Failed again..
https://youtu.be/Jrc5_1hpPQY
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Old 16th Sep 2019, 5:28 pm   #59
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Default Re: Yet Another Bush TV22

The video is actually very soothing to watch!

That is, if one is not involved, of course. Though I have had a similar sort of day, befuddled by something (completely different) that's not behaving as I want.

Check the goodness of all connections, particularly grounds, I'd say. Waggle the valves.

Steve
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Old 16th Sep 2019, 5:37 pm   #60
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Default Re: Yet Another Bush TV22

Thanks Steve, I'll let it rest for bit too and then go back for a valve waggling session.

Peter
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