Pilot tv brightness problem

[old_coot88]

Hey Tim, just to cut to the chase, what are the voltages (measuring from ground) to the CRT cathode (pin 3) and G1 (pin 2)?

Since the brt. control varys the cathode voltage, what is the voltage swing lock-to lock?

Hope you're running the set on an isolation xfmr since it's a hot chassis.

[timmy]

Originally Posted by old_coot88

Hey Tim, just to cut to the chase, what are the voltages (measuring from ground) to the CRT cathode (pin 3) and G1 (pin 2)?

Since the brt. control varys the cathode voltage, what is the voltage swing lock-to lock?

Hope you're running the set on an isolation xfmr since it's a hot chassis.

Should I swing the brightness control up and down while checking these voltages or just check the voltages. And no don’t have an isolation xfmr. Lock to lock ?

[old_coot88]

Yeah, with the meter connected, just turn the control lock to lock and jot down the reading at both ends. The range can then be compared to the G1 (control grid) voltage. What you're in effect doing is varying G1 with respect to cathode, and this varys beam current (brightness) in the CRT

BTW, your meter is a digital 10 meg impedance (not an old analog VOM), right?

[timmy]

No old analog meter I’ll check those voltages.

[timmy]

Using 3kp1 crt pin 3 -50v brightness up and 67v brightness down and pin 2 -120v brightness up and no change in voltage brightness down. No antenna used.

[old_coot88]

Hm.. lessee. G1 fixed at 120V. Cathode (pin 3) has negative 50V, positive 67V. That's a total voltage swing of 117V. That seems like a gawdawfully large swing. Are you sure the neg50V is correct?

[timmy]

Originally Posted by old_coot88

Hm.. lessee. G1 fixed at 120V. Cathode (pin 3) has negative 50V, positive 67V. That's a total voltage swing of 117V. That seems like a gawdawfully large swing. Are you sure the neg50V is correct?

Yes the voltages are correct. What should the -50v be ?

[timmy]

Is -39v better or more normal?

[old_coot88]

Well, I'm gonna hafta bail on this one and leave it to the experts. With 106V positive on the grid relative to cathode, and still be showing an in-focus (albeit dim) raster is beyond credulity. Maybe a quirk of electrostatic jugs? I may learn sumpthln new here.

[old_tv_nut]

Can you check some more to see if one of the connections is maybe open? I'm thinking possibly an electrode floating freely to an unusual voltage.

[old_coot88]

The voltage chart in the Sams gives this:

Measure from pin 5 of V19 (35W4) which is raw negative 135V to:

CRT pin 2 (grid)..13V
pin 3 (cathode)...185V

Timmy's pin 2 from ground... 120V
Pin 3 from ground varies from negative 50V to +67V w/brt. control setting

So... calling all xperts

[old_tv_nut]

The DC restorer is not a restorer per se, but it is supposed to develop a varying DC on the grid based on sync tip to average ratio that tracks the same ratio that occurs naturally in the AC coupled cathode drive.

As such, it's possible that it will not work normally if you don't have a signal with picture coming in.

Can you retake the voltage readings with a normal signal please?

[old_tv_nut]

Originally Posted by old_coot88

Well, I'm gonna hafta bail on this one and leave it to the experts. With 106V positive on the grid relative to cathode, and still be showing an in-focus (albeit dim) raster is beyond credulity. Maybe a quirk of electrostatic jugs? I may learn sumpthln new here.

You missed the minus sign

Pin 2, G1 is -120, pin 3, K is -50 to +67

So G1 to K is -70 to -187, Sams says -172, so that's within range of the SAMS.

[old_tv_nut]

I think the next thing I would do is check the resistance chart readings all around the CRT and V9. Also check C41, C42, C5 for leakage.

[old_coot88]

Originally Posted by old_tv_nut

You missed the minus sign

Thanks. Geriatric brain fart.