Help with Philco 50-T1403 code 125

[jsandlin]

I have a Philco 50-T1403 code 125 with low HV about 5K. when I got the set someone had tried to recap it. I found several caps that were the wrong value and a few wiring errors. The horizonal oscillator was running at 32khz with almost no HV. After correcting all the problems I have found so far the oscillator is now running at 15750 hz with 5k HV. turning up the brightness the HV starts dropping as soon as it starts drawing any beam current. I have about 46 volts peak to peak at 15750 hz with a - 8 volts DC on the grid of the horizonal
output.

I have 2 schematics showing that the frequency should be 7875hz. Which I have never heard of but I haven't work on a set of the vintage before. What should the frequency be at that point?

Have tried new horizonal output, oscillator, HV rectifier and damper,
swapped the flyback with a known good one with no change with any of them.

[dtvmcdonald]

the 7875 Hz is the frequency of the scope sweep ... that's why it shows two
cycles of the waveform. Pictures of the vertical sweep traditionally correspondingly showed 30 Hz.

[bandersen]

Check the 680K resistor in-line with the HV anode lead.

[jsandlin]

Thanks for the information on the horizonal frequency. I have never seen it displayed like that I have always seen it as time base but it good to know for future reference.

I have bypassed the anode lead to do away with the 680k resistor temporarily.

I am completely stumped by this I have the correct drive 15750Hz 46 V peak to peak -8 to -9 volts DC on the grid 276 volts on the screen ( see picture) and 86ma cathode current on the horizonal output. with only 5 to 6 k HV.

I also have about 365 V of boost.

Any suggestions would be appreciated.

[Kevin Kuehn]

Does high voltage come up if you disconnect the anode lead from the CRT, as in no load?

[old_coot88]

Wonder if there's sufficient voltage across the 1B3 filament to sustain emission. The filament should be glowing a dull orange if you darken the room and can see up inside the tube.

[Kevin Kuehn]

Originally Posted by old_coot88

Wonder if there's sufficient voltage across the 1B3 filament to sustain emission. The filament should be glowing a dull orange if you darken the room and can see up inside the tube.

Great point. And if the 4.7 ohm filament resistor has drifted high it could have exactly that effect. It's usually soldered directly under the 1B3 socket and a pain to get to.

[jsandlin]

After the bad weather and some overtime at the job I finely got back to the Philco. Here is what I have done since last post.


The 4.7 ohm 1B3 filament resistor was 5.4 ohms and the 680K anode resistor was just over 700K. changed both with no change in problem. The horizonal grid drive is and exact match to the schematic the grid and screen DC voltage are right on and the boost voltage is almost perfect at 355 V and the pulse across the yoke winding is a perfect match to the schematic just a little low in amplitude 1350 V peak to peak the DC resistance of the yoke is correct also at just about 15 ohms. The most HV I can get is about 6K with no beam current and everything else peaked for maximum voltage. When the brightness is turned up just as it starts to light up the HV starts to drop. also checked the video and DC voltage on the CRT and they seem to be ok.

So now I am grasping for straws the 1B3 socket is kind of crusty along with the stand offs so I am going to change the socket and stand offs incase they are a little leaky very little hope that this will do anything. I have also swapped out the door knob capacitor with no change.

Any suggestions would be welcome.

[Electronic M]

I'd check how long an arc I could draw off the CRT HV cup, then unhook the HV rect top cap and see how long an arc I could get off that.

[old_coot88]

I'd also try to verify that the filament is glowing dull orange. If it's not, try jumpering the 4.7 ohm resistor and see.

[nasadowsk]

That horizontal test jack has me a bit confused. Is there a plug that should be in it during normal operation?