The PHILCO Phorum
Predicta Raster Issue - Printable Version

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Predicta Raster Issue - Haydenp121 - 06-09-2023

Hi -

I picked up a Philco Predicta Decorator several months ago. Since then I have been working on it spontaneously. It has been completely worked through: paper caps replaced, resistors replaced as needed, re-coated flyback, etc. I've been gradually working through the plethora of issues commonly associated with these sets, but I am stumped on one in particular.

The set suddenly lost its raster. The horizontal output tube briefly red-plated. Noticing the red-plating, I turned the set-off and let it sit for around a month before returning to it. Upon returning to it, I carefully turned the set on. The horizontal output tube didn't red-plate, but the raster was still absent. I used an oscilloscope to check out the signals from the grid of the horizontal output tube, grids of the horizontal mult, and both sides of the AFC diodes. Everything seems to be normal. In addition to this, the flyback tests good, and I can hear the high voltage. Immediately after pressing the power button to turn the set-off, the raster briefly reappears and collapses as normal.

This problem appeared in the past but seems to be intermittent. When the raster was present, the horizontal wouldn't lock. I feel it may be a problem in the damper section, but I don't really trust my judgment at this point.

Any ideas would be greatly appreciated!

Cheers!

- Hayden

RE: Predicta Raster Issue - morzh - 06-09-2023

You need Bob Andersen.
I do not know how often he frequents this place, but he is extremely active on Facebook Philco Predicta Club.

RE: Predicta Raster Issue - MrFixr55 - 06-09-2023

These and other sets of this vintage are notorious for cold solder joints for tube sockets and between the bard and the tabs that mount the board to the chassis. These tabs serve as ground connections and complete the ground plane for the board. Any poor joint between the board and one of the tabs will wreak havoc such as stopping the oscillator, which will redplate the Hor Opt tube, stopping the sync separator, etc. I think that the Hor Opt and Damper tube sockets are mounted on the PCB. Consider strengthening the foil traces for cathode and plate circuits and ground planes with bus wire.

462ron - 462ron - 06-10-2023

After checking the socket and foil connections and redoing the grounds as MrFixr suggested, I would take voltage measurements on the CRT. It sounds like the biasing of the grid and cathode could be off and momentarily comes into range as the set powers down thus briefly producing a raster!

Ron

RE: Predicta Raster Issue - Haydenp121 - 06-11-2023

Thanks for the advice! I re-flowed solder on the grounds, and added wiring to strengthen any possible broken traces. Naturally, I managed to mix up some wires on the main board. This resulted in smoke pluming out from R76. I don't document my work well (a bad habit) - does anyone have any photos of a 10L43 chassis main board with wiring?

Thanks.

RE: Predicta Raster Issue - Bob Andersen - 07-30-2023

Sorry I didn't see this sooner. Yes, I have some photos and many, many videos.
Do you have the service info? All the connections are clearly labeled. Every stake on the man PCB is assigned a code and the schematic and assembly diagrams show what they go to.

Not sure if these are going to help but here you go
https://flic.kr/s/aHsjbdc3vW
https://flic.kr/s/aHskwTtvPz
https://flic.kr/s/aHsmebYXWJ


Here are many videos on my Predicta restoration projects:
https://youtube.com/playlist?list=PL4aHiwoXvLGDyk8_QzFGLYdMcR5seR4b4

Here are tips on restoring Predictas:
https://youtube.com/playlist?list=PL4aHiwoXvLGDPeRjl9d98cyIZi6F71YBw

RE: Predicta Raster Issue - radiorich - 10-08-2023

Hello Hayden,
Any progress on the tv yet ?

Sincerely Richard