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.

[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?