A Cogging Pye V110

[Mikey405]

Hi Frank and David.

we both seem to be thinking along the same line.

Ha ha. I think we're ALL thinking along the same lines.

I've already replaced the 3 x 16uF caps in the block underneath (the can was heating alarmingly and they wouldn't reform). I can see no sign of video or anything nasty on any of the HT rails. I've also replaced the 500uF cap in the cathode of the video amp as well as all the resistors in the cathode too.

I will check the output of the detector diode and see what we get.

Thanks both.

Kind regards.

From Mike.

[FERNSEH]

I will check the output of the detector diode and see what we get.

Thanks both.

Hi Mike, I was going to suggest that. See what the video waveform looks like at the grid of V6A the video amplifier.

DFWB.

[Mikey405]

Hi David.

The video waveform looks (deep and) crisp and even at the g1 of the PCL84 on the min and max settings of the contrast control. The only difference I can think of is that the sync pulse at the g1 of the sync separator is much smaller at lower contrast so any "slope" or any phase difference between the lines is going to be much smaller too.

[peter_sol]

I suppose it couldn't be sound on vision could it?

[Mikey405]

Hmm. The sync does wobble a tiny bit line-to-line straight from the detector diode. Probably only a difference of, say, 5-10mV at most. The wobble does seem roughly to correspond to the black / white castellations but it's difficult really to detect. Is the sync-sep going to be that sensitive?

[Mikey405]

Hi Peter.

I suppose it couldn't be sound on vision could it?

Thank you for the suggestion but alas no. The cogging corresponds with the castellations on the sides of the picture on the test card and it doesn't appear to be affected by the sound.

Thanks for the suggestion anyway Peter.

Kind regards.

From Mike.

[FERNSEH]

Good suggestion. In the Aurora isn't audio test tone locked to the syncs?

DFWB.

[FERNSEH]

Hmm. The sync does wobble a tiny bit line-to-line straight from the detector diode. Probably only a difference of, say, 5-10mV at most. The wobble does seem roughly to correspond to the black / white castellations but it's difficult really to detect. Is the sync-sep going to be that sensitive?
_________________ A few millivolts shouldn't matter much. In a direct line sync TV the horizontal displacement would be clearly defined, the flywheel sync softens things up a bit. That's what it's meant to do.

DFWB.

[Mikey405]

Hi David. The Aurora sound is turned off and there is no music playing through it either.

[Mikey405]

Hmm. I wonder if there is video on the AGC causing different amplitude line by line...

[Mikey405]

Hmmm. No.

[Mikey405]

Sync straight from the cathode of the detector...

[Nuvistor]

The disturbance appears after the frame sync pulse then settles down , well it appears to me like that, if you unlock the frame osc does the disturbance ripple through, just wondering about the frame osc/output getting into the signal path.

[Lloyd 1985]

Hi Mike,

finally got to the set! It's playing up after being in storage... But I did manage to get the measurement from pin 2 of the PCF80, if you still need it. I took 3,

contrast set at MAX = -45V

contrast set at MIN = -5.4V

Contrast set to where picture is just about to become unstable = -15V

Hope that is of some use. I know I said I'd scan the manual for you earlier, I'm having some trouble locating it currently

Regards,
Lloyd.

[Mikey405]

Thanks Lloyd. That's brilliant. Those are almost exactly the readings I get too. I think the voltage reading on the ERT sheet is wrong.

However... the problem is now solved - and blow me if it wasn't just cross-talk between the video lead and the PCF80 line oscillator valve. I discovered that when I had my hand near the line oscillator valve the symptoms were reduced. Borrowing a screening can from one of the EF80s and putting it round the PCF80 line oscillator caused the problem to disappear entirely. Also dressing the video-to-sync-separator lead away from the line oscillator also entirely cured the problem.

Anyway, there's one for the fault-report-books. Thank you to everyone concerned for your kind help and ideas. I'll post a picture of the set working shortly.

Thanks all.

Kind regards.

From Mike.

[Lloyd 1985]

How strange!

My set was acting up when I took those measurements, when tuned into the Aurora the line scan would collapse, and pulse on and off. After I took out the PCF80 to see which pin was pin 2 and put it back, the problem had gone away...

Pleased you found it in the end!

Regards,
Lloyd.

[Mikey405]

Originally Posted by Mikey405

Hi Peter.

Thank you for the suggestion but alas no. The cogging corresponds with the castellations on the sides of the picture on the test card and it doesn't appear to be affected by the sound.

Hi Peter again.

My apologies for sounding quite so dismissive of your suggestion - I just re-read the post and it did seem rather rude. It was not intended at all. Thank you for the kind idea though Peter.

Kind regards.

From Mike.

[FERNSEH]

Just been swotting up on the video circuits of the V110. The lead lengths between the signals board and the timebase are rather long so likely there will be some radiations from those leads getting into parts of the circuit where we don't want such things to do so. The brightness control varies the cathode volts of the CRT rather than the usual control grid. The triode section of V6 functions as a white spot inverter which feeds the anti phase peak white video to the CRT grid so there's another source of video signals causing interference to other circuits.

DFWB.

[Nuvistor]

Excellent and a good picture as well.

[peter_sol]

Hi Mike I did not take it as rude at all I have seen some rude comments here from time to time but we all mean well and take an interest.
I am pleased you sorted it out.