1966 GE PortaColor Restoration

[jr_tech]

Originally Posted by Dubis7

Would this replace X1?

https://www.ebay.com/itm/5pcs-1N2071...UAAOxynhFRBp5P

No... the diode you listed is a zener diode, you just need a common rectifier diode like a 1N4007.
https://www.amazon.com/MIC-Silastic-...s%2C358&sr=8-4

not affiliated,
jr

[Dubis7]

Good thing I asked, then. I'm sure the codes in the service manual match specific products that are long out of production.

Part ordered. I needed to pick some of those up anyway. Fingers crossed this fixes my power supply issue.

[Dubis7]

X1 is replaced and I have life again. Out of circuit, it tested completely open.

Still having the height issue. I'll update once C2D comes in and I do the swap.

[Dubis7]

Okay,

C2D has been replaced. I'm not seeing any change.

For good measure I also swapped in a new vertical output tube. Also nothing.

I measured the ohms on R5. It peaks just around 2K, which I belive is what it's supposed to be. When I measure the voltage output coming off of R5, which is listed at 15V in the schematic, I'm seeing it maxing around 22-25V and brushing at 15V at the lowest.

Any suggestions for what to check next?

[jr_tech]

Shouldn’t the cathode go to zero volts when the pot is at one end?

jr

[Dubis7]

Let me double check. I know it looked like it dropped off right at the tail end.

I'll grab a video of the voltage and resistance readings today. Maybe you'll be able to interpret it better than I can.

I'm wondering if my issue isn't in R5. I have no idea how likely that is, but could I have damaged that?

[Electronic M]

Portacolor sets are somewhat prone to tin whiskers in the pots...I had one which had the AGC pot dead shorted to ground via a tin whisker. The set had ZERO reception and it took some time troubleshooting the dead IF to trace it back to the AGC and then the pot...if a whisker developed on a pot connected to B+ or boost it could make the set really unhappy.

[Dubis7]

Here's a video where I took some measurements on R5. https://www.youtube.com/watch?v=aBqK...ature=youtu.be

Could this be tin whiskers? How would I go about correcting that?

[jr_tech]

That jumping near the end of the pot travel looks highly suspicious... have you tried cleaning the pot with deoxit?

jr

[Dubis7]

Originally Posted by jr_tech

That jumping near the end of the pot travel looks highly suspicious... have you tried cleaning the pot with deoxit?

jr

I did, but I'm not convinced I did it right. I'm thinking I'll take another crack at it.

That being said, if I do need to replace this, does anyone know what replacement part I'd be looking for? Obviously I'll check Moyers with the part number first, but assuming they don't have a replacement.

[Electronic M]

My standard process for tin whisker infested pots is to remove, and dismantle the pot take a toothbrush then fine sandpaper to the metal parts clean everything with a good control cleaner and paper towels, reassemble the pot, check resistance and range with rotation between all terminals and also case metal, and if all is good reinstall.

[Dubis7]

Originally Posted by Electronic M

My standard process for tin whisker infested pots is to remove, and dismantle the pot take a toothbrush then fine sandpaper to the metal parts clean everything with a good control cleaner and paper towels, reassemble the pot, check resistance and range with rotation between all terminals and also case metal, and if all is good reinstall.

Okay. I'll give this a try. I'm going to just remove the pot, disassemble it, and deep clean it.

One thing I am sort of wondering about, and I can get pictures of this if you need it: I'm noticing that the pot doesn't have the standard three lugs. Instead, it has one that goes to C2D/the main PCB, and two that connect to ground. That matches the schematic just fine, but since this is unusual, is there anything I should be watching out for as I disassemble?

[Electronic M]

Originally Posted by Dubis7

Okay. I'll give this a try. I'm going to just remove the pot, disassemble it, and deep clean it.

One thing I am sort of wondering about, and I can get pictures of this if you need it: I'm noticing that the pot doesn't have the standard three lugs. Instead, it has one that goes to C2D/the main PCB, and two that connect to ground. That matches the schematic just fine, but since this is unusual, is there anything I should be watching out for as I disassemble?

That just means it is configured as a variable resistor instead of a variable voltage divider...One benefit of this configuration is if one of the end lugs is open but center never goes open you can make the open end lug the grounded one and continue to use it(max and min vs rotation may swap).

[Dubis7]

Okay, well I really went at it with the deoxit on R5. Not seeing any change.

Are we sure this can't be a HV problem? Or maybe a voltage problem? My HV to the CRT is still measuring between 7 and 10 KV. It should be around 15 per the schematic.

[Dubis7]

I may have something here.

I'm noticing that my voltages are consistently 10 or so volts higher, except the HV which is several KV too low. I traced it back, and discovered that C103 has 0 volts when measured against ground.

I've ordered a replacement. Could that be related to my issue?