1966 GE PortaColor Restoration - Page 8 - Videokarma.org TV - Video

Dubis7 · #**106** 12-09-2019, 04:03 PM

Okay, new update video: https://youtu.be/WAhnuri57XQ

I've replaced all the remaining caps from C1 and C2. C1 is now within the correct temperature range, and anything that could have been stressed from previous mistakes in C2 is new.

And actually, the buzzing seems better. So I think that was the right move.

Here's my current remaining issues:

- The vertical is still not hitting the bottom half of the screen.
- That color bar is still visible.

I feel like I should say that I really jumped into the deep end with this one. At this point I'm entirely out of my element. But I don't want to give up!

So basically from this point on, I'm standing by to hear what measurements you would all like to see to move forward. Personally, I'm wondering about the health of the yoke and/or flyback. I say that because my HV is several thousand volts too low, and the yoke could be contributing to my vertical issue. Is there a way to check that?

Tony V · #**107** 12-09-2019, 04:43 PM

As far as the vertical issue, you need to check all the components around the vertical osc. and output tube. A bad cap or out of tolerance resistor in this area would cause the issue you showed us. I doubt very seriously that it's directly a yoke problem.

jr_tech · #**108** 12-10-2019, 01:01 PM

“I say that because my HV is several thousand volts too low”

How are you measuring HV? Are you sure the probe/meter is properly calibrated?

jr

Dubis7 · #**109** 12-10-2019, 02:01 PM

I'm using a Heathkit IM-5210. Looks like this: http://lcweb2.loc.gov/master/mbrs/re...%20IM-5210.pdf

Perhaps that's not a good choice for this? I presumed any meter was as good as any other but I could be mistaken.

Dubis7 · #**110** 12-10-2019, 02:03 PM

I wonder if it would be worthwhile to measure the voltages across each pin on the vertical output tube. Is there a tool that would allow me to access those points with the tube in the socket? I've heard of tube extenders but I don't know if I've seen them for compactrons.

old_coot88 · #**111** 12-10-2019, 02:24 PM

Quote:

Originally Posted by Dubis7

I'm using a Heathkit IM-5210. Looks like this: http://lcweb2.loc.gov/master/mbrs/re...%20IM-5210.pdf

Since there's adequate width, adequate brightness and no blooming, I wouldn't be concerned about the HV. Troubleshooting rule 101 is tackle the most obvious problem(s) first.

Dubis7 · #**112** 12-10-2019, 02:41 PM

Quote:

Originally Posted by old_coot88

Since there's adequate width, adequate brightness and no blooming, I wouldn't be concerned about the HV. Troubleshooting rule 101 is tackle the most obvious problem(s) first.

To be fair, I'm not sure I'd call the brightness adequate. The picture is only visible when I turn the control nearly to the top. That's new, by the way, it wasn't like that when I started, it started doing that around the same time the vertical got wonky.

old_coot88 · #**113** 12-10-2019, 08:15 PM

On the color issue, what voltage do you have on pins 3 and 10 of the 8BU11 (plates of burst amp and sub-carrier amp)? Should be around 200V on both.

What's the voltage on pin 9 (screen grid)? Should be around 120V.

On the vert issue, since replacing C2 didn't fix it, check the plate load resistor of the vert.oscillator. It is a high failure component in all makes/models of tube TVs due to being hammered by high level spike. And by golly Sams shows this set using a thermistor as plate load resistor. Check this. It's designated R64 (R54?). Print is blurry. It goes to the plate (pin 11) of the 11FY7. What's the voltage on pin 11? Blurry print looks like it says 290V (this voltage will vary with the height control setting, since the control is in series with the thermistor).

Dubis7 · #**114** 12-11-2019, 02:31 PM

Okay, I ran some measurements. Here's what I've got. These are all from the test point to ground using DC voltage on the meter unless otherwise noted.

Regarding the 8UB11

Pin 3 is reading around 200 V (it leveled out around 208)
Pin 10 is reading around 200V as well (it leveled out around 216)
Pin 9 is reading just about 0V

Regarding the 11FY7

Pin 11 is reading around 130V

For the thermister (R64 from what I can tell on the SAMS) I measured the resistance across it from cold, and then when the set was running. It measured a little over 1 mohm cold, and then reduced to around 1.4 Kohms.

Obviously there's some wonky voltages on the 8UB11 pin 9 and 11FY7 pin 11. How does R64 look? Shouldn't that reduce to nearly 0 ohms?

old_coot88 · #**115** 12-11-2019, 07:58 PM

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 · #**116** 12-11-2019, 10:12 PM

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 · #**117** 12-12-2019, 10:29 AM

Quote:

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.)

jr_tech · #**118** 12-12-2019, 02:16 PM

“verify that there is Boost at the height control”

Boost voltage is also connected to the Screen pots... perhaps if boost is low, it could be the cause of the perceived brightness problem?

jr

dieseljeep · #**119** 12-12-2019, 08:42 PM

Quote:

Originally Posted by jr_tech

“verify that there is Boost at the height control”

Boost voltage is also connected to the Screen pots... perhaps if boost is low, it could be the cause of the perceived brightness problem?

jr

Make sure the Boost capacitor is good. It's the one on the PC board, .1 @ 1000 volts.

Dubis7 · #**120** 12-12-2019, 09:46 PM

Ran a couple tests tonight. Need to slide the board out a bit to access the resistor for the 8BU11, so I'll plan to do that this weekend when I have more time.

I think I'm getting closer. I tested the boost voltage off of pin 3 on the flyback and the boost point on the height control. I can get 670V on the flyback (it was around 620 when I first tested, but I was able to get it up to 670 by turning the horizontal control) but the pin labeled "boost" on the height control is stuck around 250V. Again, this is all in DC.

So what's in between those two points? Is it just that capacitor? I think I know what you're talking about, and I actually replaced it already. Perhaps it got damaged when I miswired things earlier? I can see about ordering a replacement. Or maybe it's a different cap than the one I'm thinking of.