Peto Scott TV169 Restoration.

[ppppenguin]

Well done on an unusual and rather bodged up set.

One of the points of a testcard is to show up sync problems by the use of castellations. It's a stringent test.

[Jac Janssen]

A good result on an extended job Trevor. Projection sets certainly have their specific additional problems.

It was lot of work, but with a good outcome.

Jac

[Murphyv310]

Hi
Thanks guys for the encouragement.
The sync looks fine on the scope with no encroachment of video. Like I say it's perfect on test card C on the Aurora. One other thing that can cause the effect is poor EHT smoothing or the total lack of it. Not an issue here though.

[`FRANK.C]

Well done Trevor great result.
A lot of work but well worth it.

Frank

[`FRANK.C]

I haven't compared but I suspect the rise and fall times from black level to peak white may be quicker on the test card in Hedghog compared to Test card C thereby giving a harsher test.

Frank

[Murphyv310]

Good point Frank.
With the Hedghog displaying test card C it was fine.

[ppppenguin]

I haven't compared but I suspect the rise and fall times from black level to peak white may be quicker on the test card in Hedghog compared to Test card C thereby giving a harsher test.

Frank

That seems likely. Aurora's testcard is a full frame image derived from the analogue input. Hence its risetimes etc should always be system legal. Frank's Hedghog testcard is produced by an algorithm. I don't think it has controlled rise times though I'm sure Frank will correct me if I'm wrong.

[`FRANK.C]

That's right Jeffrey. I had thought about it but it wouldn't be very easy to do.
The only place that I have slowed the rise and fall times is at the start and end of the white castellations as that was relatively easy.
The start/end of the white castellations takes 2 pixels or approximately 0.23 uS to rise/fall.

Frank

[ppppenguin]

One limitation of the Aurora is that the only way of getting a testcard is via the analogue video input. Hence it's at the mercy of the accuracy of the analogue signal and any minor imperfections of the decoder. There was no simple way of putting a digital testcard file into the Aurora's flash memory. It could have been done, but not in a way that was easily accessible to the user.

Frank, in your programmable converter it might be worth having a USB or other port so that a full frame testcard can be programmed into flash memory. Or possibly having an SD card slot so that it can read a testcard file directly. I think Karen Orton showed it was possible to read an SD card directly at uncompressed video speed.

[Geordie McBoyne]

The attachment shows the CRT protection circuit employed in the Ferranti 24K5 projection TV receiver.  One half of an EB91 and an ECL80 is used.  My interpretation of circuit operation is as follows. In that normal use the triode-pentode is non-conducting by the application to the control grid of the triode section the rectified negative going flyback pulse present a the anode of the frame output valve. The flyback pulse from the line output transformer is supplied to the pentode control grid.  Failure of either timebase will result in the ECL80 becoming conductive and reducing the brightness control voltage to a low level thus causing the CRT to be cut-off.

Geordie McBoyne.