Mighty Monarch of The Air

[VintagePC]

Looks to me as though something is clamping the vertical sweep wave... i.e. it's rounded off on the bottom instead of a nice sawtooth.I'd be tempted to say it's a passive component (resistor, capacitor) that's the culprit, but if that's the case, you'd see it at the top of the sweep too.

Does anything happen if you adjust the vertical centering control, and if so, can you bring the top edge of the raster in to view?

[vts1134]

I don't know where the vertical centering control is on my set. I don't see mention of it in the schematics.

[old_coot88]

Originally Posted by vts1134

....I also adjusted the vertical controls to see if I could get an aligned picture but the picture above is as good as I could get it. I'm not sure if you can tell by the picture but the bottom of the picture is brighter than the top... Any ideas on where to head next?

Try jumping a known-good electrolytic across C1 (the 100mf one going to the cathode [pin 8] of the 6V6). That's exactly the effect you'd see if that cap were open. oc

[jeyurkon]

The bottom is brighter than the top because the vertical linearity is way off. It could be an adjustment, or a symptom of another problem.

[old_coot88]

Originally Posted by jeyurkon

The bottom is brighter than the top because the vertical linearity is way off.

That's correct.

It could be an adjustment, or a symptom of another problem.

An open (or absent) electrolytic (C1) on the cathode of the output stage will cause severe non-linearity with insufficient sweep at the bottom. I'm wondering too if the problem isn't related to T2 (the coupling xfmr.) being different from the original.. and also if this difference is gonna cause the vert. frequency to be off. oc

[vts1134]

I don't have another 100uf cap to replace C1B, nor do I have a capacitor tester. What I did do was fire the set up and take a visual check, then remove the cap that is in place and fire it up again. There was no change at all in the picture. I'll get another 100uf cap and try swapping it in.

[VintagePC]

Originally Posted by vts1134

There was no change at all in the picture. I'll get another 100uf cap and try swapping it in.

Seems to confirm what everyone says... Fingers crossed once you get that replacement!

[vts1134]

New cap same problem . Might R3 be the problem? I've tested it for impedance but could it fail in another way? I'm going to try again to get the real replacement for T2 to eliminate that from the equation also.

[old_coot88]

Originally Posted by vts1134

New cap same problem .

Well doggone. Did you connect the + end of the cap directly to pin 8, and the other end to ground? (Some foreign-sourced electrolytics have an arrow pointing to the [-] end of the unit, which can trick you as to which polarity it's signifying.)

Might R3 be the problem?

Not likely if it measures (approx.) 5K and shows no dead spots or drop-outs throughout its rotation.

I'm going to try again to get the real replacement for T2 to eliminate that from the equation also.

[vts1134]

R3 reads 5k on the high side and just a couple of ohms on the low side. There are no dropouts or dead spots in the rotation. C1B used to connect to pin 8 with a wire. I removed the wire since I was no longer using a multi stage can and now have the electrolytic directly on pin 8 and the negative right to ground. Here's hoping a new T2 will be the answer.

[VintagePC]

If you have the proper resistors to match the new T2's resistance to the original, you can try that too. I doubt it would work, but if it does, it might save a few bucks on trying to locate a matching part elsewhere.

[vts1134]

New transformer same problem . I will return to the schematic for component by component tracing soon.

[VintagePC]

Sounds like it's time to break out the scope

Tracing waveforms can get you a good idea of where the problem lies. Do you have a reference of what they should look like? (Usually in a Sam's)

Also, if you have substitute tubes, it may be worth trying those too. Some sets drive them to their design limits, and the result is a set that works perfectly with one tube, but not another that is slightly out of spec. Both tubes will still test good, of course, so the easiest way to find this problem is what's called the "tube roll" (swapping tubes in the problem areas with another one).

[Phil Nelson]

Originally Posted by VintagePC

the result is a set that works perfectly with one tube, but not another that is slightly out of spec. Both tubes will still test good

I have found that to be the case with oscillator tubes, especially. Sometimes I have had to swap in several horizontal oscillator tubes before finding one that the TV "liked."

Speaking of oscillators, are the voltages on V13 still as far off as before?

Looking at waveforms with a scope seems sensible. This schematic doesn't give models, but you could start by looking at the grids of V13 (oscillator) and V14 (output) and posting photos of what the scope traces look like there.

Phil Nelson

[old_coot88]

Originally Posted by vts1134

New transformer same problem . I will return to the schematic for component by component tracing soon.

Well tarnation. Just out of curiosity, what voltage are you getting at the low/wiper end of the vert. size control? oc