RCA 21-D-7177 Horz Drive Issues

[Kevin Kuehn]

Originally Posted by Penthode

I would be curious to see how the video fits properly within the video signal lines up on the raster eg. video starting 10us after horizontal sync. This would indicate if the retrace is timed correctly, that is the beam arriving at the left with a slight margin prior to scanning the active picture.

Terry,

You sort of lost me here. I'm not exactly sure what you're asking, or how to go about checking for it.

Thanks again for all the help, I'm learning stuff.

Kevin

[Penthode]

Originally Posted by Kevin Kuehn

Terry,

You sort of lost me here. I'm not exactly sure what you're asking, or how to go about checking for it.

Thanks again for all the help, I'm learning stuff.

Kevin

Hi Kevin,

From your earlier photos, it appeared as if the horizontal retrace time was too long. That would mean that as the beam is swinging back to the left and if the active video in the signal begins to modulate the CRT beam before the beam reaches the left, then stretched ghost like images (including the white line) will appear in the picture. That is why when you adjust the horizontal hold, the white vertical line moves to the left when the picture moves to the right.

Note that about 10us is allowed to for retrace in the signal. The set has to to be able to retrace within the 10us.

A good test for retrace time is to see if you can see the edge of the active video on the left. When you shrink the scan or shift the raster so you can see the left of the image, up the brightness a bit and you should see a narrow black vertcal band prior to the vertical edge of the active picture. If you do not or if you see the image folded over, then something is wrong.

I only mention this because I had the impression something was wrong with the retrace time from your photgraphs. The same fault also may affect linearity.

Can you hift the raster to the right and photograph the left of the picture?

Thanks,

Terry

[Kevin Kuehn]

Hard to see in these pictures, but I don't see the black vertical bar on the left side. You can just make it out on the right side.

I've also noticed that the picture is off centered to the left while using a 8XP4 self focusing test crt. Even with the width turned all the way down(narrow), I can't ever see the left edge of the picture. So it does seem this set has a slow horiz retrace problem.

[Penthode]

Hi Kevin,

That is interesting. One extra thing: your set uses the synchroguide horizontal oscillator control. The optimum sync position is with the horizontal hold turned to the right just before it loses sync. If the range of your horizontal hold is not sufficient, then you can turn the hold control fully right and slightly adjust the horizontal frequency slightly so that it just loses sync and back up so it is in sync.

If you have to adjust the coil, make sure you adjust slightly the frequency coil end and not the horizontal waveform adjustment on the other end.

Can you still not see the black stripe on the left? If not then we will have to investigate the retrace time.

Terry

[Kevin Kuehn]

Originally Posted by Penthode

Hi Kevin,

That is interesting. One extra thing: your set uses the synchroguide horizontal oscillator control. The optimum sync position is with the horizontal hold turned to the right just before it loses sync. If the range of your horizontal hold is not sufficient, then you can turn the hold control fully right and slightly adjust the horizontal frequency slightly so that it just loses sync and back up so it is in sync.

If you have to adjust the coil, make sure you adjust slightly the frequency coil end and not the horizontal waveform adjustment on the other end.

Can you still not see the black stripe on the left? If not then we will have to investigate the retrace time.

Terry

Terry,

I'm not so sure this TV uses that exact horiz oscillator circuit. Take a look at the schematic below. I don't see the separate horiz frequency control you speak of. All I have are the horiz hold, and the horiz waveform controls. The horiz hold on this set is a coil (L40 on the schematic). RCA called this a deluxe model TV, but it sure seems to be missing a few key circuit adjusting controls.

[Penthode]

Hi Kevin,

Thanks for the diagram. It is a synchroguide circuit. Only the horizontal hold control isn't a portentiometer in your set: the control is the coil itself. If I recall correctly, your set may have a limter to prevent adjusting it too far. Try adjusting the horizontal hold so that the image moves to the right at the point just before it loses sync. That is the optimum point in a synchroguide circuit and that should provide a good reference to examine the left hand of the picture.

Is it possible to post the damper circuit?

Thanks,

terry

[Kevin Kuehn]

Here's the damper section. Hope it's enough.

[Kevin Kuehn]

Ok... with the horiz hold adjusted so that the picture is farthest to the right(before loss of horiz hold), there is still no dark bar present on the left side of the picture.

I can see both sides of the picture as the set warms up and the picture slowly expands across the screen. There is clearly a bar on the right side.

I did recieve in the mail this week a set of Merit replacement yoke and flyback transformers. I've yet to try those. I'm not looking forward to replacing the flyback. I'll try the yoke after I wire up a new octal plug for it. I may also need to order a new balancing cap for half the horiz winding.

[Kevin Kuehn]

This is interesting: With the line voltage turned down to around 85-90 volts, we do seem to have a black bar on both sides. But I'm also seeing some waving of the scan lines over on the left. You can also clearly see the horizontal linearity is off.

BTW, this is now using the little 8XP4 crt.

[Penthode]

Reducing the line voltage provides a clue. The reduced line voltage will lead to reduced horizontal drive. There might very well be a problem with the flyback transformer. But, I wonder if it is simply a matter of too much horizontal drive?

Have you tried reducing the drive and increase the width?

Terry

[Kevin Kuehn]

Terry,

I've wondered about the horiz drive being too strong. I normally have the drive cap turned all the way closed (min drive), but that could possibly still be too much. Any suggestions on how to further reduce the drive? Could I lower the value of the HOT grid resistor, or add more capacitance across the variable cap?

[Kevin Kuehn]

FWIW, I do have the correct voltages around the HOT.

[Kevin Kuehn]

Another thing: I have not replaced C105 (560mmf mica) because the horiz drive waveform looks fine. Plus I don't have a 560 @ 1kv.

In fact I have not replaced any mica's in this chassis, only the paper and electrolytics.

[Penthode]

Kevin,

You seemed to have already done everything I can think of.

Not too long ago I had a similar problem on another RCA chassis. All the voltages were about correct and the horizontal drive was turned right down but the right hand side was compressed. I swapped the horizontal output tube which tested good otherwise. Same problem. I figured it had to be the tube.

I then bought a couple of NOS tubes from Ebay, swapped the tube again and "voila" the raster filled out on the right.

I know you said earlier you had swapped the tube. Was it a NOS tube and what is its condition?

Terry

[Kevin Kuehn]

Terry,

I have at least a half dozen nos 6DQ6's. Honestly I've probably only tried 2 or 3 besides the one original to the set. Never got anywhere, so I gave up on that direction, it's still a possibility.

But, if the right side "were" compressed, would that also be causing the left side picture to be cut off (no horizontal space bar?) I didn't think it would do that.

It sure would be interesting to have the actual RCA service literature for this chassis. Possibly there are notes about scan issues.

Does anyone know what was used for pincushion correction (if any) on this TV? Watching this 8" test CRT, the pincusion effect is really bad.