I measured R297 and it was spot on 39K.
Replaced it with a 100K resistor because the pot was at maximum resistance.
This put the Vertical Hold close to the middle.
But, still my Vertical is slowly moving.
Sorta like the Vertical Sync pulse is not syncing the Vertical Oscillator.

I'm not entirely sure where the Sync pulse gets to the Vertical Oscillator.

Carl

Look at the grid of the vertical oscillator. Just ahead of that there is a series string of 3 resistors with 3 capacitors to ground. That is the circuit that filters out the horizontal sync pulses and passes on the vertical sync pulse. That circuit is connected into the vertical oscillator through a capacitor connected between the last resistor and the grid of the vertical oscillator. Look for any mis-wiring or wrong value parts in that area.

Hi Carl,

The sync pulses get into the vertical oscillator via the "vertical integrator" network, which in this set is R293, R308, R309, C306, C307, and C308. Check all of those components and make sure all the capacitors are replaced, even the micas in this particular network, since one could strongly suspect a problem in this part of the circuit. Also double check to make sure there are no wiring errors from any previous components replaced in this part of the circuit.

(Hi Tom S. - Looks like we posted simultaneously. Good to see our answers agree! )

Thanks Tom and Tom.
I appreciate your insights with this.
I replaced all the capacitors and checked/replaced resistors.
Could it be a "leaky tube"?

This morning I'll go back and double check all these capacitors, resistors and wiring. I'll also put my scope on the control grid and plate of vertical oscillator V10A. Looks like the Sync Pulse goes to the plate of the vertical oscillator (V10A) and then to the grid of V10B - am I seeing this correct?
Then one lead of the Vertical Output Transformer routes around to the primary of the Flyback. Could that 19BG6 HO tube have a leak with the Filament?

BTW, my vertical height was such that I had to set the vertical height control to max. When I replaced the 6SL7 (Phase Inv & Clipper), during search for my vertical hold problem, upon replacement of this tube I got plenty of control of the vertical height.

Carl

All the Vertical Sync pulses on the grids/plates/cathodes on both Triodes of V10 match Riders in both voltage level, and waveshape. Also, the waveforms look like 60hz on my Scope.

I just noted on Riders Trouble Shooting Chart "#8 Picture Jumpy" that this could be caused by "Gassy or noisy 19BG6" or "Noisy sweep or sync circuit tubes". I did note a blue color inside the 19BG6. I've ordered one off Ebay so hopefully this will fix this issue.


The 10BP4 tested weak for Cutoff in my Sencore CR70
I removed my test CRT and mounted the 10BP4.
It has marginal focus - the Sencore manual predicted weak Cutoff indicates poor contrast.


Carl

Not quite. The feedback loop that makes the circuit oscillate is from the plate of V10A to the grid of V10B and then from the plate of V10B back to the grid of V10A through C296 and R295. The sync is from the cathode of V11B through the vertical integrator circuit to the grid of V10A, where it mixes with the feedback from the plate of V10B. The sync signal causes the vertical oscillator to cycle just a little bit sooner than it would by itself. So in normal operation the vertical hold is adjusted so that the oscillator would naturally run slightly slow so that it is almost ready to cycle when the sync comes along. Then the sync comes along and says "do it now".

That "W" version of the circuit is a little more obscure than the early version.
I think your explanation jiggled my memory. Is V10A and V10B essentially an "astable multivibrator"?

I'm going to try another resistor for R297. R297 measured exactly 39K and I put in a 100K. I think I'll try something inbetween - say 68K.

I got in a 19BG6 replacement tube but there was no improvement.

Still looking. I wonder if the problem is something to chassis ground - say the secondary speaker transformer or a leaky Vacuum Tube.

Carl

Carl,

Yes, it's a multivibrator.

If you want to check the sync pulses without seeing the much larger self-oscillation pulse from the vertical oscillator, simply pull out the vertical oscillator tube. If you then probe the sync pulses at the socket with an oscilloscope, you'll be able to see whether they are making it to the tube.

When you pull the vertical oscillator on this set, you will unfortunately upset the balance of currents being supplied by the power supply to various parts of the circuit. Most likely you'll be OK, but keep your eyes, ears, and nose alert for trouble. Also, it's a good idea to turn down the brightness, since this will put a very bright horizontal line on the screen that could possibly burn the screen if you leave it there a long time.

Just a few more circuit comments -- you mentioned earlier that the vertical oscillator is connect to the flyback/horizontal output stage. This is actually what is called the "B Boost" power supply. When the horizontal output stage and flyback transformer are in operation, they function as a source of B+ that is a little higher voltage than the main B+ supply of the set. The vertical output stage needs a bit more voltage to function properly; that is why it is done this way.

Regarding the picture tube and focus: If you swap the picture tube, the focus is likely to need readjustment. On this set, there are several things involved: 1) setting of front panel focus control (which is really just a fine focus adjustment); 2) position of back panel coarse focus adjustment switch; and 3) position of focus magnet on neck of CRT (which also will have some interplay with the exact position of the ion trap). You'll likely need to fiddle with all of these when using a different CRT. Although your CRT has a funny setting on the bias on the CRT tester, in practice I find that many CRTs which show this actually function quite well in the set. So your CRT may well be just fine.

Coming back to your B+ voltage problem -- We appear to have found that the problem is not due to excess current in the 25L6 audio output stage. The other big current hog in the set is the horizontal output. Have you checked the drive level to the horizontal output yet? If the drive level is low for some reason, it can cause excess current flow there. The voltage chart in Rider shows you should see a DC voltage of -40 VDC with respect to B1-. Are you near that voltage, or something lower (which could indicate insufficient drive)?

For now, I think your low B+ problem and the vertical sync problem are unrelated. They might have a common cause that we'll find later, but for now it looks like two separate problems.

I forgot this is a series-strung filament set, so you won't be able to run it with a tube pulled. You can watch the scope for a few seconds after you pull the tube, but that's all. This particular approach really only works well in sets with a transformer feeding the filaments in parallel. Sorry about that!

Well technically one could pull the tube and plug a power resistor (who's resistance and power rating can be calculated from ohm's law based on the tube heater rating) in to the heater pins of the socket and run the set without the tube for a prolonged period.

My .02$.

Tom C.

Well, if you have some clip leads you could pull the tube and reconnect the filament with clip leads.

Is the horizontal sync solid or is it somewhat touchy? If the horizontal sync is solid then there must be a good signal at the cathode of V11B. In that case the problem has to be in the circuit consisting of R301, R291, R292, C300, C291, C292 & C293. Have you replaced C293?

If the horizontal sync is touchy (the lock is weak), then you probably have a weak signal at the cathode of V11B. In that case you will need to troubleshoot the circuits of V11A and V11B.

Thanks Tom. My circuit is the "W" version and it has a different circuit for the Vertical Sync.

Here is the "W" schematic:
http://cerant.com/TV%20GE%20805%20-%201 ... /SD/SD.pdf

I highlighted in Yellow the capacitors and resistors I replaced. Note that the V Sync goes into the Vertical Oscillator differently than the Early Version.

Hoping to go back at this issue tomorrow. That the audio amplitude jitters the video might be a clue. When I turn the volume all the way down, it does not jitter the video. But, in both instances the Vertical Hold does not sync.

Carl

That is unusual to apply the sync into the middle of the vertical circuit like that. I see that the sync comes from pin 2 of V20 and goes to both the horizontal and the vertical circuits. If the horizontal sync is solid and stays locked over a reasonable portion of the rotation of the horizontal hold control, then you can assume that the sync coming out of pin 2 of V20 is good. In that case, with the parts you replaced, the vertical should sync. Several things to check. See if you might have replaced a resistor with one that is 10 times the correct value. Do a similar check on the capacitors. Also remember that new parts are sometimes bad. If you could run the set with the vertical tube pulled and do something about the missing filament, you could scope the sync from V20 through the integrator circuit.

A question. Looking at the schematic in my prior post, the Focus Control is in the Audio Output circuit. How does the Focus Control function?

Carl

That certainly seems odd to me, too.

This is actually quite common in these early sets. The focus coil needs a certain amount of current flow to work properly. The designers simply look at the total circuit of the set and figure out where there is appropriate current flow that can be "borrowed" without upsetting the function of another circuit. In this set, the cathode current of the audio output tube is used for that purpose. By various bias adjustments on the audio output tube, the current flow through the focus coil is adjusted. Meanwhile, the audio output stage still functions normally, although in some cases there is a slight effect on sound volume as the focus setting is changed.

As I mentioned a number of posts above, in one of my Locomotives, there was a problem with grid emission in the audio output stage. This had the effect of causing the focus to drift and the volume to change.

Here is the Scope photos:


The top waveform is the Vertical Oscillator - V10, pin5.

The bottom waveform is the Sync Pulse - left side of C308

Apparently the Oscillator just will not sync.

Carl

I can see a very small amount of the signal on pin 5 being back fed to the left side of C308 and a very very small amount of the signal on the left side of C308 showing up on pin 5. I would expect to see much more of that signal showing up on pin 5. I think that C308 is either bad or not the value you think it is (such as being 47 pf instead of 470 pf

The strange thing is that I just replaced C308 with a yet another 470pf disc capacitor. Then I installed two .001uf orange dips in series, and then a .005uf. Still the Vertical Hold sill not sync. But the waveforms look like this with the .005uf:


The picture will not lock in vertically. I've swapped out V10, V20, V22, and V21 but no joy. Could 60hz be getting in there somewhere? This has been a really strange problem.

Carl

Yes, that can happen. The vertical rate is almost but not quite 60HZ. If you were locking onto 60HZ, there would be a setting of the vertical hold control where the vertical would stop rolling fast and instead stably roll slowly. It would take something like 5 seconds to make one full roll. If you are getting contributions from both 60HZ and the sync, the vertical would mostly roll slowly but jump a little once per roll.

There are two ways to get 60HZ into a circuit. One is heater to cathode leakage in a tube. The other is excess ripple on a power supply voltage.