Help me identify this Zenith?

[AlanInSitges]

Ladies and gentlemen, BEHOLD

The (slightly blurry) schematic for a PAL Zenith. It has some important differences from the Sams I've been using as a reference. I'll do a clearer scan later today.

Crossing my fingers I'll be able to get this going.

[old_tv_nut]

That's a unique slice of time, with tubes, transistors, and analog bipolar ICs.
Very nice!

[AlanInSitges]

Here's a cleaned up and more legible schematic. The entire sweep and HV section is different than what I've seen in the Sams, including the damper and HV Regulator tubes, which had the numbers illegible in the set. B+ is lower than the Sams version, and it's exactly what I have measured, so hopefully things will make more sense now . I'm going to start again using Tom's suggestions and the new schematic and values and see where that leads.

Zenith B4519WKT - 1 (PS, Sweep, IF)

Zenith B4519WKT - 2 (Video, Chroma, Sound)

[AlanInSitges]

OK, I could use a little more help here...

B+ is low across the board. Main B+ is supposed to be 390V, I have 350V even with the HO tube removed. I only have 355V before the choke. Adding the HO tube makes it drop by a couple of volts. So there is either something wrong with the B+ supply or there is something dragging it down. The filter cans don't get warm even after 15 minutes, R399 that big dropper resistor is hot but not more than I would expect for a 15W resistor. And even though the B+ is low, if everything else were working, I should still have HV, right?

Moving on to the horiz/HV section: the HO output tube is hot, but according to two different meters I put in series with that cathode fuse it's not drawing any current. Well, one says 0 and the other says 1mA. Fuse is good. There is drive on the grid, measured -48V and about 300V drive from the 6U10 that looks like the Sams picture. However! The screen is quite high, at 160V. Now here is where I could use some help. Please disabuse me of my misconceptions and half-understood leaps of logic:

1. If the B+ is low, and the screen, which is fed from the 390V B+ through a couple of resistors, is high, that would indicate that the tube isn't conducting, right?

2. If the cathode current measures 0, that would also indicate that the tube isn't conducting, right again?

3. Where does the HO tube get its plate voltage? The only path I can find is the 390V on the secondary of the vertical output transformer, that goes through the vertical centering control and makes its way to the plate of the damper. It would follow that the damper is conducting from plate to cathode, over to the flyback, and then to the plate of the 6LB6. Am I right? That seems...convoluted. It must be for a good reason.

4. I am starting to suspect there might not be plate voltage on the horizontal output tube. Except! When the damper is in the set, I can hear the vertical output transformer thumping away. When the damper is removed, no more vertical. Since the vertical output tube gets its plate voltage from the selfsame 390V that's on the plate of damper, that means the VO tube isn't directly dependent upon Boost being present. However! The vert osc gets its plate voltage from Boost and nowhere else, so this must mean that there is Boost present, which must mean that the HO tube is indeed conducting, or there wouldn't be boost present. Which means my plate voltage theory is wrong. But I want to verify before I just stick a probe on there and vaporize a perfectly good $15 DMM.

OR, is there enough of that 390V dribbling through the damper circuit to run the vert oscillator? In which case it would be safe to measure the plate on the HO tube and get a clue where to go next.

I cannot figure out for the life of me where the 870V Boost is coming from. I have re-read both Grob and Gulati on this subject but I'm getting lost.

Thanks everyone for your guidance.

[AlanInSitges]

Question: who's got two thumbs, enough knowledge to be dangerous, and a Zenith with high voltage?

Answer: 👍 this guy 👍



'Twas the HV regulator socket, had come unsoldered from the chassis and ungrounded several things. Tomorrow I'll clean the tuner, send it a real signal, and see if it makes any color. Very exciting. thanks again for the help everyone.

[Electronic M]

Great news there.