1966 GE PortaColor Restoration

[old_coot88]

Sounds like the thermistor is probably OK since it's not going open. Have you verified there's Boost voltage going to the height control? Should be around 600V or more.

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.

[Dubis7]

I'll check that the next time I'm at my workbench. Might be tomorrow or Friday night.

I'm still wondering about whether the thermistor is dropping enough. Let's say I were to jumper it with a wire, just to see what would happen with zero resistance. Would I be risking causing any damage?

[old_coot88]

Originally Posted by Dubis7

I'm still wondering about whether the thermistor is dropping enough. Let's say I were to jumper it with a wire, just to see what would happen with zero resistance. Would I be risking causing any damage?

Well, you'd be applying full Boost voltage directly to the plate of the vert osc with the Height control at full rotation, which wouldn't be good.

First, verify that there is Boost at the height control. If there is, try subbbing in a few resistors for the thermistor. I'd try something like 22K, 47K, 100K, 470K, 1 meg. If there's no improvement in the height, then the thermistor's not the problem.

(A decade box for R substitution 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).

[old_coot88]

So... is the set now producing a color picture, with proper tint control range?

[Dubis7]

I think so. I at least know all the voltages to the tube match.

I may need to call in someone to verify for me on whether it's "proper" though, since I'm color blind.

How do I tell if the range is proper? Would a video help here?