RCA 621ts Restoration

[old_coot88]

Originally Posted by vts1134

The white bars roll right along as I adjust the vertical hold out of lock, and back in place when I adjust the vertical into lock.
I'm not sure how much ripple would be needed to cause a symptom like that but G2 has in the neighborhood of 3VAC present on it without any signal injection.

Well that rules out G2 and leaves only the cathode of the CRT. Try this for the heck of it- hook that 10mf electrolytic from ground to the cathode (observing polarity of course) and see if the bar remains.

One other thought- After doing the cathode shunt, try shunting G2 with the 10mf cap. Hook its neg. end to top of C116B (which carries smoothest B+) and the positive end to G2. This will effectively kill all ripple on G2, just in case the 3VAC is sufficient to cause the bar.

Maybe it was the butler in the library with a pipe wrench?

Maybe he was in the library with a wench.

[vts1134]

Originally Posted by old_coot88

Well that rules out G2 and leaves only the cathode of the CRT. Try this for the heck of it- hook that 10mf electrolytic from ground to the cathode (observing polarity of course) and see if the bar remains.

One other thought- After doing the cathode shunt, try shunting G2 with the 10mf cap. Hook its neg. end to top of C116B (which carries smoothest B+) and the positive end to G2. This will effectively kill all ripple on G2, just in case the 3VAC is sufficient to cause the bar.

Negative on both counts .
I also did the grounded screwdriver trick to spots on the dag with the set on to check grounding of the crt and it was ok.
Could it be the tube itself?

[Electronic M]

I'd try running the filament of the CRT on it's own transformer to rule out hum leakage from a heater-cathode short.

[vts1134]

Interesting suggestion. What kind of amperidge would that need? The schematic calls for 8A on the heaters for everything else, but no rating on the CRT filament.

[Electronic M]

I don't know the exact specs, but probably around 800mA should be enough. As long as the filament is not running more than 1 volt high or low it should be safe for a quick test.

[old_coot88]

The CRT heater already has its own dedicated 'floating' winding in the power xfmr, designated 'Y and YZ', going to 'KIN' (for kinescope, the archaic term for CRT).

Try this- unplug the CRT from the socket and check for heater to cathode short with the ohmeter on highest range. It should read infinity (although a short might occur when the heater warms up). Also check DC resistance form the floating winding to ground. It should also read infinity, but double check the schematic to verify this, and that it's not connected to B+.

With the set on (and the CRT reconnected), measure the DC voltage between heater and ground, and see if it reads the same as the cathode (or not). Ideally, it should not if it's truly 'floating'. Then try shunting the heater to ground with the 10mf cap, first from one side of the heater and then the other. And see if the bar remains.

[vts1134]

Originally Posted by old_coot88

The CRT heater already has its own dedicated 'floating' winding in the power xfmr, designated 'Y and YZ', going to 'KIN' (for kinescope, the archaic term for CRT).

Try this- unplug the CRT from the socket and check for heater to cathode short with the ohmeter on highest range. It should read infinity (although a short might occur when the heater warms up).

It reads infinity on the Megohm scale.

Originally Posted by old_coot88

Also check DC resistance form the floating winding to ground. It should also read infinity, but double check the schematic to verify this, and that it's not connected to B+.

It has a path to ground, but it's connected to B+

Originally Posted by old_coot88

With the set on (and the CRT reconnected), measure the DC voltage between heater and ground, and see if it reads the same as the cathode (or not). Ideally, it should not if it's truly 'floating'.

It reads a different voltage than the cathode. Heater reads +225V and cathode reads +195V, which I see is a little low so I took a measurement where it should read +425V and it only got +350V. It's right on the 20% mark but it looks like I'll be going resistor hunting at some point to address that.

Originally Posted by old_coot88

Then try shunting the heater to ground with the 10mf cap, first from one side of the heater and then the other. And see if the bar remains.

The bar wins this round.

[old_coot88]

Originally Posted by vts1134

...(CRT) cathode reads +195V, which I see is a little low so I took a measurement where it should read +425V and it only got +350V. It's right on the 20% mark but it looks like I'll be going resistor hunting at some point to address that.

Actually the exactitude of these voltages is not all that important as long as you have a bright, in-focus pic and the brightness control has proper range. Having the proper bias relationship between K and G1 is what's important, not so much the voltages themselves relative to ground.

[Reece]

Why is the heater connected to HV? Is that to reduce the potential and the arcing possibility between it and the cathode?

[old_coot88]

Originally Posted by Reece

Why is the heater connected to HV? Is that to reduce the potential and the arcing possibility between it and the cathode?

Exactly.

[old_coot88]

By golly now that we got more of the schematic to eyeball, there's one more CRT element, the focus electrode or "G3" that hasn't been shunted with the .1 (or .25) cap.
Try clamping it, with the cap going from B+ to "G3" (pin 6). If the bar still remains, Mr. Earlyfilm has an idea i hadn't thought of yet:

Originally Posted by earlyfilm

VTS1134,

I see the vertical section attempting to run at 120 cps and it is badly speed modulating the sweep resulting in dual white bands. In other words, the normal 60 cps sawtooth is being speed modulated by a two backwards steps at a frequency of 120 cps.

Hah. "Speed modulation" of the v sweep waveform itself. That's an idea worth exploring.
IIRC, VTS1134 has a variac. While troubleshooting a vert problem in his vintage Majestic set, the idea was floated of driving the vert. yoke winding directly with the variac. Even though it's a pure sine wave, if it were tried on this set, it would at least reveal whether the bar is sweep derived (ie., 'speed modulated' sweep) vs. a rogue pulse on one of the CRT elements.

[tubesrule]

Originally Posted by old_coot88

By golly now that we got more of the schematic to eyeball, there's one more CRT element, the focus electrode or "G3" that hasn't been shunted with the .1 (or .25) cap.
Try clamping it, with the cap going from B+ to "G3" (pin 6).

The focus anode is sitting at around 1500V so even bypassing to B+ is still way over 1000V. Better have a cap rated for this.

[old_coot88]

I wuz just goin' by the schematic which calls for approx. 495V (varies with focus control setting).

[old_coot88]

The 'ghosting' doesn't look like the smearing/ringing of fine detail you typically see with IF misalignment.
What happens if you inject video at the CRT grid, working back point by point? Have to reduce the B&K's output as you move back (to keep the pic from flagging) and reverse the phase a time or two. See at what point the ghosting appears.

[old_coot88]

You've probably already checked 'em, but there's two more peaking coils, L103 and L104 that you might want to doublecheck for continuity.
If those are good, what happens if you inject video from the B&K at the CRT grid, working back point by point towards the 6H6 detector diode? Need to reduce the output as you move back (to keep the pic from tearing/flagging) and reverse the phase a couple of times (since a tube's plate is always opposite phase from the grid). Also watch for the point at which the 'trailing ghosties' appear (that's assuming they arise after the detector in the video chain).