Kuba PAL PortaColor on E-Bay Germany

[old_tv_nut]

Originally Posted by yagosaga

http://fernsehmuseum.net/kuba/img/Po..._colorbars.jpg

Meanwhile I have found one fault of the bad colour reproduction. The 7.8 KHz coil has a break, so there is no switch pulse input for the colour demodulator.

- Eckhard

Yes, my first thought was NTSC demodulator on PAL signal - the R-Y cancels out due to alternating phase of the signal without correcting phase switch in the R-Y demodulator.

[yagosaga]

Originally Posted by old_tv_nut

Yes, my first thought was NTSC demodulator on PAL signal - the R-Y cancels out due to alternating phase of the signal without correcting phase switch in the R-Y demodulator.

It is Simple PAL. I.e. an NTSC demodulator with alternating R-Y signal. Here are the schematics:

http://fernsehmuseum.net/kuba/img/CK211Pschematics.jpg

Kind regards,
Eckhard

[Robert Grant]

Thanks for posting this schematic. I had always wondered how the R-Y was "switched" (on this set, I guess the phase of the 7.8 KHz osc forces the "wrong" diodes to cutoff the undesired output of the R-Y demod).

It must be in there, but I don't see how the set "knows" which lines are R-Y, and which are Y-R.

[zenith2134]

Another one saved. Thanks for the pics; very cool.

[Mikey405]

Well done Eckhard for rescuing that Kuba set. I kinda-like those sets. They always feel like they'll drop to bits at any minute when you pick them up and the picture always seems fuzzy on those low-definition tubes, but they do have a kind of charm about them.

Originally Posted by Robert Grant

It must be in there, but I don't see how the set "knows" which lines are R-Y, and which are Y-R.

Hi Robert. With 625 line PAL, each alternate line has a burst signal which "swings" +/- 45 degrees relative to the previous line. This "swinging burst" is then rectified to generate a 7.8KHz (half line frequency) square wave which then operates the PAL switch so that the R-Y synchronous demodulator recieves a reference signal in the "correct" phase relative to the signal.

Hope my dodgy explanation helps. Probably does more harm than good.

Kind regards.

From Mike.

[yagosaga]

Hello Jerome,

recently I have acquired another Kuba Porta-color on the British ebay. It was sold in non-working condition, "suitable for spares or repair", so I could win it for a low price. I wanted to take the 7.8 KHz coil from this set for my first set. But fortunately, there was only a small soldering problem at the anode connector of the PL504. After a few minutes this set works fine.

The tint control of Simple PAL is a little bit tricky. When I change the input source (test pattern, DVD or aired broadcasts), I have to readjust the tint control. With fine tuning of the channel, the white tone also changes. You see, I have to go through the circuits.

But now, I have the chance to measure the 7.8 KHz coil for getting the values to design a replacemend for the other set.

P.S.: The emission of the 11SP22 in this British Porta-color is 0.4 mA on Blue, 0.4 mA on Green, and 0.4 mA on Red, similar to what I have measured on the other picture tube.


Kind regards,
Eckhard