1966 GE PortaColor Restoration

[old_coot88]

According to Sams there should be solid continuity (zero ohms) from pin 3 of the flyback to the Height control. Since there's only 250V at the Ht control, find out where the open is. That .1 cap is not a problem if you already replaced it.

Also see if there's Boost at the screen controls. As jr_tech mentioned, if it's low it will knock the brightness down.

[jr_tech]

WAG.... the wire/run between the HV cage and circuit board that carries the 670v boost voltage to the screen and height pots is broken or cold soldered... the 250 volts measured on the height pot is actually from the 270 volt supply back feeding through the screen pots.

jr

[old_coot88]

So... if indeed there's no Boost at the scr. controls, turn all 3 down to minimum before the Boost is restored to them. Otherwise, the CRT will be overdriven and may bloom out, an unfamiliar situation for a noob.

[Dubis7]

Okay, precautions were taken as suggested. Screen controls were minimized before I started poking around again.

Sure enough, no boost voltage at any of them. In fact, the entire boost line on the PCB was dead.

So I checked the wire. Wire was good, but there was no continuity to the board.

It turns out that the same solder joint for the wire linking to pin 3 on T4 is also used for the connection to the .1uf boost capacitor, which I replaced. Apparently when I did that, the solder didn't flow properly around the boost supply wire and left it essentially hanging in midair. It was hard to spot, but when I was actually looking for problems at that joint, it was obvious that the solder had pooled around it and wasn't actually connecting.

Moreover, I've identified the source of that HV sparking, and it wasn't the flyback. As soon as I pulled the board out, I saw sparks shooting from that solder joint. Apparently they were jumping between the gap and periodically supplying boost voltage, which explains why the picture kept filling out.

So anyway, I resoldered that joint. And sure enough, I have full deflection again!

Now I can focus on a few other issues. The color sounds like it won't be hard to tackle, and I'll plan to focus on that next since I have the board loosened and accessible.

I'm also still concerned about the brightness. It seems like the picture goes completely dark for a significant portion of the control. Not as much now that boost has been restored, but still more than I'd like. Maybe that's the nature of these sets? Or does that sound like a tired CRT? I don't have a tester with me, but should I start keeping an eye out for a replacement?

Now that boost is restored, an old issue has come back. I'm noticing those flashes of bright light again, and they aren't impacted by the brightness.

I've taken a video of the progress at this point. I'd like to fix the color next, but I also made sure to capture the flashes so you can see what I'm talking about. Any thoughts on what that might could be?

Here's the video: https://youtu.be/LEAJsa0N-FU

[damen]

That type of flashing was usually caused by a defective video output tube. Will not show up in a checker, only way to tell for sure will be to sub the tube.

[old_coot88]

Tap the tubes gingerly with something like a screwdriver handle. It'll usually show up any intermittencies. Tap around on the board too. The 'tap test' was an integral part of troubleshooting back in the day.

Temporarily disconnect anything from the ant. input just to be sure that flashing isn't 'hitchhiking' in from outside the set.

[Electronic M]

That 'flak' looks a lot like the RF noise from a motor running picked up by the TVs RF system.

[Dubis7]

Okay, brief update. I'm pretty sure the video output tube is causing it.

I was able to get the lines to start and stop by tapping the 11BT11. I've gone ahead and ordered a NOS one, so I'll see if that fixes it. I've also been noticing that the sound and video keep dipping and then coming back, almost like the signal is being muffled. Tapping that tube seemed to correct that as well.

As far as motor interference being picked up, this happens regardless of the location in the house, and there aren't any nearby motors. So I think it's internal to the set.

[old_coot88]

Since another section of the 11BT11 also contains the sound/sync amp, that could also be affecting the sound as you mentioned.

Incidently, see if the contrast control varies the intensity of those flashes (it's located on the furthest-to-the-right end of the back apron).

[jr_tech]

“I'm also still concerned about the brightness. It seems like the picture goes completely dark for a significant portion of the control. Not as much now that boost has been restored, but still more than I'd like”

Where are the screen controls set?

jr

[old_coot88]

There doesn't appear to be any kine bias or brightness range adjustment. If it turns out more brt range is needed, there's a little bit of "engineering fudgery" that may improve it. Just jump a resistor from brt. control wiper to ground. I'd start with 2 meg to be conservative. Then work downward in R value till desired range is reached.

What it does is make the CRT cathodes more negative, hence the G1s more positive with respect to the cathodes.

Again a decade box would be handy

[Dubis7]

Originally Posted by old_coot88

Pin 9 of the 8BU11 is fed thru a resistor (blurry print looks like it's 100 ohms, can't read the R designation). There should be 130V on the supply end of this resistor. Is there? If there is, the resistor must be open, giving you the 0V you're getting on pin 9. Does the resistor look cooked?

There's a .01 cap from pin 9 to ground (can't read the C designation). It might be shorted. Or possibly a short in the tube.

So jumping all the way back to this. I went ahead and tested the resistor in question. It's hitting around 140V on each side. I'm not seeing any significant drop in between. I'm gonna recheck that. It's buried very deeply in and difficult to reach with the probe. But assuming that's correct, does that sound correct to you all, or does that seem unusual that there's no significant voltage drop across the resistor, even if there is continuity?

As for the .01 cap, how would I go about measuring that?

I suppose I could also sub a tube to be safe as well. I reverified that there's no voltage on pin 9, so somewhere between that resistor and pin 9, I'm losing voltage. Maybe a cold solder joint? I haven't done any soldering there as of yet, but I've heard solder joint issues are a common problem in portacolors.

[old_coot88]

On the foil side of the board, look for a crystalized joint where that resistor's lead comes thru the foil, or where pin 9 comes thru the foil. If there is, re-flow the joints or tack a wire between the two joints.

[Dubis7]

I'm still waiting on that video output tube to come in, but I wanted to check in about something I'm noticing.

When I turn the brightness down, the picture grows much larger and the vertical seems to bob up and down. It doesn't lose sync, but it's significantly impacted for a moment.

Is that normal? Is that a sign of an issue?

[Dubis7]

Also, a quick update on the color problem.

Since my vertical is finally back, I decided to go ahead and plug in a video source to get the geometry locked again. In doing so, I noticed that I was no longer seeing that color line.

I wasn't happy with how cramped measuring on the top was, so I decided to do a few voltage tests from the bottom. I had to remove an RF shield to get there, but I was able to uncover the pins for the 8BU11. Reverified pins 3 and 10, those are still a little above 200V, but now pin 9 is reading just above 130V. So it looks like whatever wasn't working is now working again.

My current theory is that the tube pin itself was dirty. I never did clean those, probably should but I always get so excited to dig into the obviously bad capacitors that I skip that step. I've removed that tube a few times and I'll bet in the process of removing and installing it, I eventually cleared the block. I'll keep an eye out to see if it comes up again but I'm cautiously optimistic.

So right now my only remaining issues are the bad video output tube, which is on its way, and possibly that brightness issue I pointed out. Once I fix those, I can clean up the cabinet a bit, do some geometry and color adjustments, and this thing should be good to go (hopefully).