Portacolor got the wiggles

[AlanInSitges]

As long as my scope is in AC mode I should be able to see the same waveform on the plate of the oscillator, no?

[old_tv_nut]

So, let me understand - you put your scope probe on the grid of the horizontal OUTPUT, and the horizontal OSCILLATOR quits?

[AlanInSitges]

Yes. It's a recent vintage CRT analog Tektronix.

[old_tv_nut]

Originally Posted by AlanInSitges

As long as my scope is in AC mode I should be able to see the same waveform on the plate of the oscillator, no?

I think C265 is large enough to make that correct.

[AlanInSitges]

I'll give it a try and see where that leads, thanks.

[old_tv_nut]

Does the oscillator also die when you probe the plate?

[old_tv_nut]

The -4 volts on the oscillator grid could be suspicious. It corrresponds to the high plate voltage. It says that the phase detector output voltage is low but the oscillator/hold coil is tuned to offset it.

Since this is closed loop operation, it is difficult to say if there's a foult or where it is.
Start by measuring the oscillator grid voltage while turning the hold control from unlock on one end to unlock on the other, and see if -2 volts grid occurs somewhere within the locked range. If the grid voltage is always low throughout the locked range, then I would check the phase detector circuit. Maybe the first thing is to replace the tube, then look for bad components.

[old_tv_nut]

Wild thought: is the 270V supply clean? Possible that vertical is causing a disturbance in the supply to the H oscillator?

[AlanInSitges]

Well, I turned the set up on its side again to take some measurements and noticed that it was back to the Horiz-Vert bouncing again. I turned it back over to try to get video, and...it was only moving vertically. Horiz was solid but vert was bouncing like crazy at the top of the screen but hardly at all at the bottom. This HAS to be some kind of intermittent bad connection, I thought, and spent the entire afternoon poking, prodding, twisting, wiggling tubes and components, tapping all over the circuit board, moving wires all over the place to see if wire dress could be the root of the problem, and...nothing. It sat there with only the vertical problem for two hours. I turned it over a dozen times. I ran it upside down. Nothing!

I got an idea that maybe this was related to convergence or magnetism or who knows what else, and grounded the grid of the VO tube to take that out of the equation. I got a straight line, no large movement, but it's still jumping a tiny bit. Feeding in a crosshatch, I was able to clearly see that the pattern of horizontal movement is not present. In the attached video you can see the line moving slightly, which I suppose is a clue. https://photos.app.goo.gl/WhGtJnhDhqmjUFdw9


So here's where I am:

I don't know why the problem has manifested in two different axes at different times. I went back this afternoon and messed with it for another half hour and it continues being only vertical. I am going to try to solve the vertical problem right now and worry about the other one if I see it again.

The fact that the vertical line exhibits a bit of movement at a similar 2-5Hz frequency, even though the vertical oscillator is disabled makes me think that...I'm not sure. That line pretty much can't move unless there is current flowing through the primary of the VO transformer.

Schematic https://i.imgur.com/MVZOy8J.png

The only things that could cause that line to move without the vertical oscillator running are:

1. Maybe the convergence coils but looking at the schematic they are in series with the yoke so, I guess not.
2. Some stray magnetic field but I'm confident there is none.
3. Maybe the vertical output tube is still conducting current even though its grid is grounded. (Is this possible? I need to measure the voltage on the cathode). IF it is still conducting a bit and we still see our problem on the screen, then we can assume that the problem lies in the circuit between the 270V B+, which I believe is clean, the VO transformer, output tube, and that bypass capacitor. It can't be much else. Please point out any holes in my logic, I'm trying to learn.

My plan of attack for tomorrow is:

1. Watch the B+ line with an analog meter and/or a scope to see how clean it really is.
2. Check the voltage on the K of the VO tube; it should be 0 if not conducting and have some voltage if it is (lin control is set to middle of range). This would be a good place to check with scope as well.
3. Determine the defective component based on the above tests. The earlier problem in the H axis makes me suspect that 270V supply but I watched it for a little while today with a DMM and it only bounced around 20-30mV.

Barring that, well, I guess ghosts.

[zeno]

At this point I would look for a H-K short in one of the
tubes.
Without a checker you can pull most tubes one at a time
& the raster will stay a few seconds to see if it goes away.
With a checker you may find it or you may not. You just cant
trust a checker.

73 Zeno
LFOD !

[damen]

I know on the US sets GE sometimes used the mounting lug of the terminal strips for ground connections to the chassis, but they were only screwed onto the chassis, not soldered. Loose screws or oxidized metal would cause strange symptoms.

[AlanInSitges]

Well, back to this...with some resolution, I guess. Today I decided to hook up my DVB tuner to my HLLY low-power transmitter and try to remove the pattern generator from the equation after another several hours of beating my head against this wall and blowing 30€ on sweep tubes. The HLLY is set for NTSC UHF channel 25, with standard 4.5MHz audio.

The DVB box has a unique feature in that you can switch its baseband output between PAL and NTSC, regardless of what the input format is. It plays MP4s from USB as well. So I set the box for NTSC, tuned in the PortaColor to UHF channel 25 and...exactly the same thing, jiggling picture. What a letdown. So it's not a problem with my signal source, this TV really is haunted.


OR IS IT?


I wanted to try changing some settings on the DVB box and the PortaColor was jiggling so much I couldn't even see the menu screen so I hauled out an old GEE (that is not a mistake) B&W CCIR-B set that has a good picture on it and tuned the UHF tuner to the frequency of my transmitter. Jiggling like a MF. What? I could at least see enough to go through the menus and switch the output to PAL and the picture stabilized instantly. I didn't even have to adjust the holds.

So I hooked up my pattern generator (A Philips PM-5515TX) to the GEE set and jiggle city. I set the Philips back to PAL B, rebooted, and nice stable picture on the GEE. AARGH.

So, it is a problem with my signal source. Both of them in fact. Both of them are European products operating in a PAL world that let you set them to NTSC for one reason or another, and both of them exhibit exactly the same weird artifacts when used that way.

I'm at a loss for where to go from here. This is incredibly frustrating. Much of the frustration is of my own doing, I realize, wanting to working on these American sets instead of being content with the tons of Philips (and GEE!) that are here and were designed to work on the current and signals I have easy access to. But the heart wants what the heart wants.

I'm going to take a couple of days off and then see if I can get the PortaColor to produce a stable picture when fed a PAL signal. Color is another issue of course, but one thing at a time. I've also got a mint Predicta Holiday I restored last summer sitting on a shelf because I thought I wired the power supply wrong and how much you wanna bet it's the same problem?

[old_tv_nut]

Does the Portacolor HE use an integrated circuit in the sync section? If so, this could be a problem with it not liking an NTSC signal that doesn't perfectly match all the details of FCC standard sync. This was a problem with some US sets (particularly Zenith) when video games with non-standard sync first came out.

[AlanInSitges]

Oh, no...it's all tube. Even the horiz AFC.

[AlanInSitges]

Who's got two thumbs, is in way over his head, and has a nice stable picture on his PortaColor?

��THIS GUY.��

Switched the pattern generator to PAL B and instantly got a nice stable picture on the GE. No color of course, and the V and H hold are both near the end of their range, but there you go.