Repair service help for a ferguson 991T

[Geordie McBoyne]

Attachment shows the line output stage of the Ferguson 991T. Ringing (velocity modulation effect) can be caused by failure of the components associated with the linearity coil L26. C31 and damping resistor R43.

Geordie McBoyne.

[AdrianPH]

The TV is in pieces at present, going through alignment I have found a broken core on L13, so the can is out whilst I find some quick set araldite.

Adrian

[Murphyv310]

Attachment shows the line output stage of the Ferguson 991T. Ringing (velocity modulation effect) can be caused by failure of the components associated with the linearity coil L26. C31 and damping resistor R43.

Geordie McBoyne.

Indeed David.
Have you looked at the OPs photo off screen, not Striations (velocity modulation) I would say.

[AdrianPH]

Well after a bit of time I got the core back together and moving free in the core, but it has made no difference. I went through the static tuning the best I could, L13 is not peaking but gives a better response to 17.75 MHz when fully in, looking at the circuit I am not sure what it is meant to resonate with as I see no cap associated with L13. It was previously fully in the core and I think it had locked in place over time for it to break when I tried to wind the core back out .

On the Striations I will admit to believing it is not that, the book I mentioned before has the same picture as shown by Freya, different page layout and it suggests that it would be worse on the left hand side and disappearing as the dot moved to the right, to be started again by flyback etc. As I see mine as being even across the screen I have basically thought to myself the line timebase is OK?

The next step for me would be to lift the earth on my scope and connect up, But I will admit that is something I am loathe to do, but guess I will have to.

I may just try something with the Hedghog first, as in power it from a battery just to make sure the PSU I am using is not putting any noise on the output. I am finding the tones quite noisy from the Hedghog and it all goes quiet when I turn the test card off. So think I need to eliminate that and then bring the TV into my room with the PC and try with the Hacktv signal.

Adrian

test card not tones.

[ppppenguin]

This may be a silly question but are you using an attenuator between the HH and the set? If not, you're likely to be overlaoding the set. 10dB to 20dB is about right.

[AdrianPH]

Not a silly question but no, not using an attenuator, not considered it I do not have any that fit the F connector output. I had assumed the output level to be similar to a normal TV modulator it goes OK into the Sony 9-90UB with out issue?

Adrian

[Murphyv310]

Hi Adrian.
Jeffrey is right. You may see on some of the alignment instructions to reduce the signal, some areas require a lower level. Surely though your signal source has a level adjustment? That would be OK so long as the signal was low enough. You might find the adjustment that doesn't peak up it may with a lower signal, if so all well and good but if not it might be a good idea to investigate why it doesn't.

[Freya]

I have seen some strange visual effects caused by placing the Hedghog on top of some sets or just too close, the flyback gets radiated back into the signal, same also goes if very thin (cheaper) coax is used. I doubt the power supply is the cause.
All Hedghogs are tested using 18dB attenuators, however some users dont use attenuation if their sets are not as sensitive.

[AdrianPH]

I am not getting any notifications of messages so if I take some time to comeback sorry.

The 991T has two sockets on the back one is attenuated and the other not, in the attenuated socket the Hedghog is noisy, in the standard one it is not, I have tried it on a stabilised power supply and still the same.  I have also just been trying it on the Hackrf-one with hacktv and I get a similar line problem so I can say it is not a problem with the Hedghog.

Here is two pictures of the while bar looking at the left hand side and the right hand side, would a problem with interlacing cause this?

       

I also loaded up a PM5544 testcard into it and these are pictures of that with the same effect as before.
   
Left hand side and right hand side.
       

Am I expecting to much from a 1954 TV.  When going through the alignment it did seem to need a fair signal, I am just not sure what to expect in all reality.

Adrian

[peter scott]

If you want wide bandwidth you certainly have to forgo quite a lot of gain. Although they are not quoting the bandwidths, here is the range of sensitivities quoted for early EMI sets in their alignment instructions. You have to assume that even with 10-15uV sensitivity that an acceptable picture was given.

   

Peter