Aurora problem

[line sync]

I,ve had a problem with my aurora from new that there is a snaking effect going up or down the screen or like a hum bar when the smoother cap is on it`s way out.
I used to run my aurora from a 12v switch mode power supply and then moved on to a 9v switch mode.
I`ve also tried a 9v stabilised supply using the well known LM317 regulator but still get this snaking effect.
I`ve also tried going threw an isolation transformer.
I cant believe the aurora is faulty so what am I doing wrong ?
Any help would be much appreciated.

Robin

[line sync]

Here is a picture to show the effect ,

[Panrock]

Hi Robin.

My instinct is some sort of modulation hum effect.

Is this seen on just one set or all sets?

Do you have another Aurora to try?

Worth trying using the Aurora with a stand alone battery too.

Steve

[Restoration73]

Are you using an attenuator - the RF output is quite high. Most of my sets will display
an acceptable picture with a 40dB attenuator in the aerial lead.

[Lloyd 1985]

You know, I'm sure I had this back in my old Daventry workshop! It was very odd, and I just used to ignore it, but one minute it would be there snaking away merrily, and not just on one set, and then the picture would bounce as if the mains supply had been momentarily interrupted, and the snaking would stop. It would come and go as it pleased, it did worry me once when I'd just replaced the smoothers in a set and I saw the picture start doing its thing! I never put it down to being the aurora though, I guessed it was something nasty getting into the mains supply.

Regards,
Lloyd

[mark pirate]

I have had similar problems with some sets, I purchased some low loss double screened coax that lessened the effect.
It is worth getting a variable attenuator as well, this makes a big difference with some of my sets. The output from the Aurora is quite strong and can cause some sets to suffer with signal overload.

Mark

[line sync]

Thank for your help guys.
I have got attenuators and have to use them from time to time but not using one on the tv in the picture.
I have had this effect on quite a few sets but I don't think its always been there.
I will add an attenuator to the above set and see what happens.

[line sync]

This evening I tried several attenuators and they had no effect on this problem.
Just for peace of mind I added an extra smoothing cap to the receiver displaying the problem but of course it made no difference.
I`m running this set at work and the building uses 3 phase mains , that's not going to cause a problem is it ?

Robin

[peter_scott]

Hi Robin,

Looking at this photo:
https://www.vintage-radio.net/forum/...d.php?t=117036 posting #10
It doesn't look as if the line sync (you have an appropriate name) trigger position is simply being shifted at the start of each line. It looks to me as if the linearity of the lines is varying i.e. timing is changing throughout the line.

If this is so then I think it's more likely to be an interference problem affecting the line output stage.

Peter

[The teleman]

I have had the same problem,
I have 2 aurora units on different channels run from independent power units & variable attenuators but still can't find the problem .
I was chasing a heater cathode fault or a smoothing fault only to find nothing wrong
Some sets do seem worse than others
I have no problem onmy Bush TV22 but on my PYE 36 I do

Chris

[D Cassidy]

Hello.
TV is not my forte so I am only passing on what was said in conversation with a good friend of mine that stays close by.
My friend has around 20 TV sets from the 405 line era and has Aurora converters for a signal.
A couple of his sets depict this problem, what he has said is there is a hum problem with the sets and not with the converter, if the converter was at fault all the sets would show the same problem.
He has replaced smoothing, heater decouplers and on at least one set all of the valves. He now thinks the problem is a leaky valve base, the problem never occurs with a cold set, it only appears once the set is fully warmed up.
I cannot comment on this as such but I have seen this problem at my friends and it reminds me of sets in the 60's with a faulty smoothing capacitor, exactly the same symptoms.
I hope this is of use to you.

[line sync]

Thanks for your comments teleman and D Cassidy.
I`m pleased I`m not alone with this problem.
Peter , what you say sounds very interesting but you lost me almost from the beginning.
All the sets I`ve had with this problem on have been fully restored with new caps , all valves tested and any re used smothers / electrolytics have been reformed.
I also have a dinosaur standards converter and was going to see if the same problem happened but annoyingly could not find all the leads to connect it up so will try again on Monday.

Robin

[peter_scott]

Originally Posted by line sync

Peter , what you say sounds very interesting but you lost me almost from the beginning.

Hi Robin,

What I was trying to say was that looking at the screen image it appears to me that the overall width of the lines is not constant as the scan progresses from top to bottom. If the fault lay solely in the Aurora then I would have thought that the waveyness on the left hand edge would be repeated exactly down the right hand edge but it's not.

Another thing that suggests this is that the black and white blocks along the top of the test card do not have their vertical sides all sloping in the same direction.

I think the problem is in your line output rather than in the Aurora.

Peter

[line sync]

Ok I`ve done quite a lot of checks and this is what I`ve come up with.
After finding all the leads I tried my dinosaur standards converter with matching modulator and used a dvd player playing a test card.
Result was exactly the same as the aurora.
Then thinking of mains supply problems I tried another mains outlet , still the same.
I then added a good quality mains filter , still the same.
I then powered the aurora from a 9v battery , still the same.
I then started trying other 405 line sets I`d restored.
The ekco TS46 had the same problem but not half as bad , a Philips 385U refused to work due to a faulty on/off switch , the bush tv22 worked perfect with no sign of the problem as did the sony tv9 90.
Obviously the aurora is not to blame and I think some of my sets may need more attention.
The derwent receiver which is the set used in this thread has had a fussy restoration and despite adding more smoothing , adding screening around the line o/p stage the problem still persists .
I don't know what to do next as others on the forum have had the same problems and I don't want to be chasing a fault that is not there.
Peter thought I may have a line o/p fault but apart from the screening I`m at a loss what to do next.

Robin

[ukcol]

In the days of 405 black and white TV transmissions the timebase sync pulses were locked to the mains frequency. I assume this is not the case with the Aurora.

When the pulses were synced to the mains any hum on the picture, caused by imperfect smoothing in the receiver, was stationary and therefore less noticeable.

Could this explain what is going on here?

[julie_m]

That might be a good idea for something to include in a future standards converter design: the option to synchronise the output field rate to the power supply frequency, or some other external reference. The ability additionally to synchronise the output line and frame rates to another video signal, even without doing any conversion, would also generate some interesting possibilities for video effects in the analogue domain.

I expect there would have been all sorts of nightmares with brightness variations, if the frame rate differed even slightly from the frequency supplied to the studio lighting .....

[Jac]

Robin,

It might be a far fetch, but I recently had a similar effect with my Pye B16T, which I was restoring.
See attached picture.
In reality the S-shaped slow movement was much more serious than visible in the picture.
The movement was also, albeit less, visible in the vertical deflection.

In the end it turned out to be caused by the choke in the power supply.
This measured the correct self-inductance at 100 Hz, but more detailed measurements showed serious anomalies.
Rewinding the mains choke gave a rock-steady picture.

If there is a mains choke in your set, it might be worth replacing it temporarily by another one, to see it this is the cause in your set as well.
With the faulty choke, the ripple on the +310V line was only 1.2VAC - I did not expect that to have this serious effect on picture stability.
First I looked elsewhere in the set, because doubling the smoothing capacitor (after the choke) didn't seem to do much.

Hope this helps.
Regards,
Jac

[line sync]

Thanks colin , Julie and jac for your comments.
The thought had crossed my mind about the 405 line transmissions being synchronised by the mains .
Some interesting thoughts there.
Jac your post has got me thinking because when I got this set the mains choke was missing so the one I used came off an old radio chassis.
I have got a few others that I could try.
I`ll sort them out and try them next week.

Robin

[Jac]

Robin,

A choke off a radio might be too small.
The current through the choke in a television could easily be in excess of 200 mA, in a radio it is more likely to be a third of that.

In the case of the Pye 16T receivers, a capacitor is connected in parallel with the choke in order to have maximum suppression at 100 Hz.
The resonance frequency of the LC-combination thus is 100 Hz, so you can calculate the L-value. Is that also the case in your set?

Hope this helps.
Jac

[Heatercathodeshort]

This is the effect seen on my both of my Pye D16T's and the two at the museum at Dulwich. The odd thing is when used with a Band 3 converter the effect is very slight. It is certainly not a problem and is not seen on a 'transmission' from the AURORA.
The 'S' shaped picture was a big problem with early Ferguson model 991T flywheel sync fringe receivers.
Many complaints were received by Ferguson but the problem was actually caused by slight incorrect phasing of the line sync particularly on outside broadcasts. I will attempt to find my notes on this and post.
Ferguson worked with the BBC to clean up the problem. Regards, John.