Repair service help for a ferguson 991T

[peter scott]

If you don't have an isolating transformer you could always ensure that your chassis is connected to neutral and disconnect the mains earth connection of your scope and let the scope float on the TV chassis potential.

Peter

[`FRANK.C]

If you get a cheep free view box that can accept a USB stick. I think most can.
You can load any image you want onto the USB stick, play it back through the box and connect the box to your Hedghog.
If I needed the black and white bars I would draw them in paint and load it onto the stick.
That's what I use when I want a particular test pattern.

Trevor (Murphyv310) had a thread about the boxes but I just cant find it at the moment.

Frank

[Murphyv310]

Hi.
Indeed the Antiference boxes have a USB input and can show any pattern you want. Its a DVBV01 model see here: https://cpc.farnell.com/antiference/dvbv...hlookahead

Re the issue it is ringing. Usually caused by poor alignment but can be caused by any damping resistors across IF coils and transformers going high value and the stage "ringing". Some sets dont have these damping resistors. It also can happen in the video amp, which may have HF correction to improve definition, a cap that has changed value in the video amp can give rise to this, look around the cathode circuitry for small values 200 to 1000pf and chokes or chokes missing or shorted out by a previous repairer.

[AdrianPH]

Looks like i missed the odd email notification, not a problem.

I should have the pattern gen sometime next week, just hope it works, the freeview box I use an old Goodmans DB5 does not have USB input. OK on lifting the earth on my scope it is something I may have to do but not something I like, my old HP182 framed 4 channel ,100MHz scope could do with replacing as it is rather large.

I have a problem on the TV today, looks like a problem with the ballast resistor either a joint or a wire break, the part number was Z8829 and is 20, 20, 60, 60, Ohms. The sheet does not give a wattage so if anyone can recommend what size fixed resistors I need to get, looks like I may need to replace the last section of it, it is in a general bad way as there are already many resistors hanging from it.

There is another resistor which is 350 Ohm at 5 Watt wire wound which is described as a Brimistor shunt, I assume that is still a standard resistor for the Brimistor or Varite X1.

Time to pull the chassis out of the case again and try and sort this.

Adrian

[AdrianPH]

OK fixed the ballast resistor for the time being a broken solder joint probably caused by movement of the wires with the mains connector.  On the last 20 Ohm stage of the ballast is still there the others have what look like 5 and 10 Watt wire-wounds.


At least with the set out of the case an a test card on it I managed to take a few pics of the screen
           

Adrian

[Freya]

Don't think thats ringing, looks like some form of timing overshoot as its an even amount after every vertical line. Bet it can be seen using the Hedghog test card and a good analogue oscilloscope.

This is line ringing
[attachment=20791]

[ppppenguin]

There may be a problem with terminology here. Freya's image is showing line scan ringing, a problem in the line timebase. The OP has a problem of video overshoot and/or ringing. This can be caused by problems in the RF, IF or video circuitry as described by Trevor. As Freya says, it should be easily seen with an analogue scope connected to the CRT cathode.

Lifting the 'scope earth as suggested by Peter Scott is potentially(!) hazardous. Many of us have done it without incident but you need to be very aware of what you're doing. Obviously the TV's chassis must be connected to neutral, which is often not quite at earth potential. Make sure there's an RCD in the supply to your bench.

[Murphyv310]

Hi.
The picture Freya is showing is Striations, it's a line timbase issue, often the linearity or width coils. Usually these have a resistor in parallel with them again to damp out the coil ringing. It also can be LOPT or scan coils. Adrian's issue is IF or Video related, I'd definitely plump for Alignment.

You'd see the issue extremely well on a Pulse and Bar test signal. (Vertical Interval Test Signal, VITS). With the scope on the video detector and then the CRT cathode which will tell you if it's IF or Video amp related.

[Murphyv310]

Hi.
Regarding alignment I've actually found that doing the "spot" alignment works reasonably well. The essence is to make sure you follow the instructions to the letter, no short cuts. it's also important to use a signal generator that is accurate and if it's something like an Advance E2 etc these are now bound to be inaccurate so let them warm up and check the output on a frequency counter. Remember that often loading up the generator it can also drift slightly so always double check the injected frequency. Follow the procedure to the letter then see what the result is like.
If you still have ringing or what we call overshoot then try and down load a simple VIT signal It can tell you a lot. You can put it on a stick onto one of those boxes I have linked to and then look at the detected waveform, On sharp changes from Black level to peak white the waveform should be reasonably square with no signs of ringing afterwards, the same should be on the opposite going from peak white to black level. On the pulse there should be no small sine waves after the pulse.

I used to have a 405 line pulse and bar stored but this is on a few computers ago.

You may find that some small adjustments are needed to give the best overall definition without ringing, note where each core is before you have a go and see what the core does on screen, keep the sound up so you can hear if it is effecting the sound channel.

The picture is a 625 line image on a French set, no easy task to get it as good as this!!

This is the 625 line VIT signal.

[AdrianPH]

OK bit of a delay in coming back to the thread, I seem to have lost what I was going to post earlier, so just decided to spend some time trying something out. 

My freeview box as I mentioned has no USB stick input and I will be receiving a Labgear CM7091 pattern generator probably next week although working condition and even if it gives composite video out I do not know?  If anyone has a manual for the unit in pdf I would be grateful for the assistance.

When I tried to do the alignment I used a IFR COM120B radio test it is fully synthesized so very stable I can not remember now if the last attempt was as per the service manual or  as a spectrum analyser to set the IF response to what I could see, it was some time ago, but I am sure I went through both methods, perhaps I will try again with the static. I could not remember getting a good indication on the AVO, perhaps I did something wrong?

I spent a bit of time reading a book called 'Correcting Television picture faults'.  This is a book that was recommended as it explains some of the terms used to describe faults on TV, so gave me a bit more insight to what people were meaning.

Lastly while I await things to arrive I have made a video which is just  Black/White/Black screen with a 1 KHz tone, this I can put through hacktv and my hackrf-one to generate a test signal. 

   

I used a package called Kdenlive in Linux to generate a 30 minute video and have it playing through my SONY 9-90 UB at the moment.  Looks like I could generate various test signals with Kdenlive but it takes me some time to do.
I will have another go at static tuning the vision IF's, I need to make up a small 1K resistor to miniature clips if I can, it would save a lot of soldering.  Oh such fun

Adrian