Cause of 'flickering' on Philco Predicta

[john116]

Hi - have finally got my Predicta in mostly working condition, with a reasonably good picture. However, it has a flickering/shimmering effect that I'm struggling to work out what is causing it.

I should say, I'm using the set in Australia, 240 volts 50hz converted to 110 volts, 50 hz instead of 60hz. Am feeding it a 525 line signal from a DVD player, and using an American RF channel 3 modulator. I have other American sets that work on 50hz with no problem, so assume that's not the issue on the Predicta.

I have a short video here, showing the problem: http://60.240.221.94/stk/predicta1.mp4

The effect is not caused by filming the screen, that's also what it looks like in real life.

Any suggestions would be much appreciated.


John

[Electronic M]

Do you know if the DVD is running 50Hz or 60Hz frame rate? If it is 50Hz that may be the source of your flickering.

If the DVD is running at 60Hz then it is probably a power supply issue (in bygone 50Hz and 25Hz regions of the US and Canada the sets made for those regions had bigger power transformers and filter caps to deal with it). Add an extra 60-300uF to the first filter caps after the rectifier and see if that helps. Could also be a 50Hz VS 60Hz issue. If the deflection is firing more often than the PS rectifires are charging the B+, then the sweep may be depleting that B+ faster than it can smoothly recover...Which may be helped by 50Hz video.

[john116]

DVD is 60hz frame rate. NTSC disc played on an NTSC player. I do have a 60hz power supply I could try it on, haven't done that yet.

[john116]

So it also does it on a 60hz 110 volt sine wave power supply. It looks like rapidly changing brightness, and also does it with no rf signal applied.

[dtvmcdonald]

Use oscilloscope on the power supply, horizontal, vertical,
video circuits.

[Electronic M]

Check tubes for heater-cathode , or heater-anything shorts...That could add a good bit of hum to things.