I start a new thread, because the old one (http://www.antiqueradios.com/forums/viewtopic.php?f=3&t=185892) was for a different problem with a different Philco Predicta Princess.



I'm back with Predicta Princess #2. Summary:
I am at my wit's end. After recapping the before working TV I now only get sound with (movie sound) and without (white noise) VCR connected at antenna - but there is no hint of any grey or white on the screen, there is not even a white spot disappearing, when the TV is switched off. All cables are connected, all voltages at the CRT (8-pin 17DRP4) seem to be ok (2.7V filament, 40V at cathode, 400V at G2, ~0V at G1 and G3). I get an arc from the anode of the CRT, when switched off, the 4 windings of the flyback have the correct cold resistances. I also verified all the dynamic pictures shown in Sam's with a scope.
Today I held a mini neon bulb near different places and it lit up near the anodes of 6DQ6, 1G3, 6DA4, and cables X and 3 of the plug to the deflection coils. I then held the neon bulb near the red anode connecting cable to the CRT outside the cage and away from the 1G3, and near the anode hole in the CRT itself: it only flickered much less convincingly. I thought I had found that red cable to be bad, but repeated all these exercises with the neon bulb using the other two Predictas that now work, with the same result (why does the bulb not show a steady glow when near the CRT anode?).
So, my question is: what could be wrong, is it the picture tube itself? I have two more Holidays, can I use their CRT's for testing the Princess?

Did you plug the Yellow? Video Output wire on to the correct pin on the chassis?
I don't know if this is true for the Princess but the Holiday has that setup and it's common to plug it onto the wrong pin when reassembling.

That's a good point. I've done that exact thing.

since he has the 40v on the crt cathode, I am pretty sure he has the video pin hooked up to the right place.

assuming you are measuring the actual pins of the CRT? does the brightness pot effect the voltage of the Pin 7 of the CRT?

On mine the 220k had drifted resulting in only a viewable pic an the very end of the range. It sounds like the HV is working but at this point a HV prob at the CRT anode would be advisable.

If that is good then I would get a scope and look at the CRT just to confirm not only voltages but waveforms.

The voltage at the anode is DC and it takes an AC voltage to excite the neon bulb. The AC voltage is capacitively coupled to the bulb (any two conductors form a capacitor) and capacitors only couple AC.

Can you verify that you can see that the filament is lit?

Yes, I did


I did not measure at the pins, because they are covered, but I checked all 6 wires for continuity.
When varying brightness, pin 7 of the picture tube varies between 5...113V.
I will try to get a HV probe and/or a CRT tester.
I not only checked voltages but also waveforms to find them reasonable


Thank you Tom, I should have known this. I wasn't sure if the (DC) electric field gradient near these hot spots was high enough to ionize neon atoms.
And - yes - the CRT's filaments light up, the voltage is around 2.7V and the cold resistance is around 2.4 Ohm.

You might be able to back off the CRT socket just slightly and get a thin probe to touch the pins of the CRT. It is unlikely, but you could have one of the contacts in the socket that is so loose that it does not make electrical connection the the CRT pin.

With the voltages that you measured, and if you have the correct high voltage (I think that you do), you should have a raster. Try running the set in a completely dark room with the brightness advanced and then see if you do get some hint of a picture.

yea, I would back off the socket and get at the actual pins, its the only way to know for sure.

They did make adapters which plug in between the socket and the CRT that allowed readings to be taken. Those aren't very common any more, but nearly every shop used to have them.

You seem to indicate in your first post that the set worked before recapping? I wouldn't think the CRT went bad in between unless something bad happened to it.

When this happens to me (and it always happens to me ) it's nearly always something I did wrong, a wire in the wrong place, a Cap stuck through the wrong hole on the PC board or similar.

I know there's no Ion trap on a Predicta so that's out.
Are you sure the HV lead is connected inside the tube shell or is the CRT out in the open where you can see it?

If you don't have a thin probe or adapter, you can wind a thin wire around one pin and leave a little pigtail hanging out to one side, and then reinsert the socket and measure voltage from that pigtail. Do this one pin at a time to avoid Bzzt.

I would second Eric's advice to double-check your work. When recapping a working TV, I try it out after every couple of replacements. If something mysteriously quits working, it's much easier to find the cause.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I made a pigtail wire with an eyelet loop and connected it one by one to each of the 4 pins 7, 3, 6, and 4 (the heater does work, so no test necessary), put the socket back and measured again the correct voltages. I bent the pins a little bit, and sprayed contact cleaner on both the pins and the socket. I jiggled the socket when the TV was running. I am sure the socket has good contact at all pins.


I did, no hint of any light, even no shrinking picture when switching off


In the beginning I thought I would find such an error in no time, as usual. I went twice through all steps I did when replacing the 14 caps, I tried to see if I lost some solder drops, no success. I then remeasured all the voltages and scope pictures and am clueless.
The HV lead is visible through the opening in the back. I jiggled on it too when the TV was switched off. When approached with my little neon bulb it flickers, especially when I move the bulb around. Here is a picture:

Do you still have that other Princess?
You could pull the tube assembly off it without too much difficulty and see if it works on this chassis, or vice versa.

Your CRT seems to have a rebuilders tag with a date of 1972 on it?

The two other now working Princesses have a 7-pin socket and Si rectifiers, whereas this one has a 8-pin socket and a 5U4 tube rectifier. I could swap the whole swivel screen including wires, which means taking the nicely working thing apart again. But I have two more not tested Holidays, where I could try to swap the picture tube?


Interesting, it says indeed "MAR 72" and the tag is hand-written. I wouldn't be so clueless, if the set wouldn't have worked before recapping. I will get a HV tester tomorrow, and see if the anode voltage is ok. Thanks for co-thinking.

Do you mean it has 8 pin positions but one is blocked out or do you mean there are really only 7 positions on the socket ? Pin 2 and 6 are both connected internally to G2 in the 17DRP4.

do you have a frequency counter? where I am going is if the horz osc is way out the HV will be very weak. Of course your HV tester will tell that for sure. can you hear the HV? if you have young ears you may be able to pick up the 15khz sound.

As the picture above shows, the socket has 8 holes, with two pins (2 and 5) not contacted, the picture tube has one pin cut (5) and one (2) internally connected to pin 6. The 7-pin picture tubes used in the other two Predictas have 7 pins and 7-pin sockets.


Yes, I have a Fluke frequency meter, I'll do the tests with it and the HV probe tonight. I don't expect much, since I turned all knobs over their ranges, when trying to find screen lighting.

Odd. I wonder what picture tube they are using ? Could someone have rebuilt a 17DRP4 with a 7 pin gun assembly and modified the Predicta socket ?

Hi Chris-was great yaking with you on the phone last nite-you have any luck with the HV probe i lent you?
what was your HV Reading?when you checked the scope waveforms on the crt-did you have the scope in dc mode?-i'm wondering if the dc that the waveform "rides on" was present?

also-i thought about it and i am willing to clear one of my messy benchs and have you drop over with that set if problems persist.we could try a skype webcam service call 1st if you wish?
those knobs i gave you work out?
Have a Good one,
RonL

Thanks Ron for lending me your HV probe. I got a sound 14.5 kV reading right at the hole, where the red cable is attached to the CRT. I measured the cathode and grid voltages both with a multimeter and with the scope, set both on AC and on DC. DC voltages are ok, cathode varies with Brightness control between 5 ... 113V, waveforms look reasonable too. So, I think next I have to replace the whole main board with one from the two other working sets. If I still don't get a picture, I am afraid to have to declare the CRT having died on the operation table.