CTC5 Pickup!

[timmy]

Originally Posted by Davala

Tube doesn't look tired

So what does the crt show on a tester ?

[Davala]

Originally Posted by timmy

So what does the crt show on a tester ?

Good question, my crt tester burned out testing a gassy tube. I'm looking now for a new one.

EDIT: I just purchased a sencore CR70.
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Matt Davala

[Davala]

I tested the 21AXP22A and it tested near new on all 3 guns. Looks like the power switch caught fire not too long after the CRT was replaced.

What do you guys do when you come across previous repairs that don't match schematics? Luckily for me I'm referencing both the sams and RCA CTC5N service manuals and they both match each other. I'm not sure exactly what the tech was thinking with some of these repairs.

Here are two of the previous repair botches. Only one of the waxed caps on top was replaced and it should have been a .01 and I found an early orange drop replacement of .0047! C108 on the sams

Underneath they really changed the contrast circuit. I tried to draw out what they did and compared it with the sams. Both the sams and RCA service data match. I thought the contrast control might have been replaced with a different value pot but its 500ohms like it should be.

I do plan to put the contrast control circuit back the way it should be.

Check out that power switch failure and fire! Thats a volume/brightness/on-off combo switch. The brightness and volume still work thank goodness. I have the power switch wires shorted. Any ideas how to replace just the on off switch?

I have currently recapped the entire top. Started on the underneath of the chassis this evening.

Hopefully I'll have this up and running in the not too distant future!
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Matt Davala

[Davala]

The resistor parallel with the cap looks like a 620 ohm but I measured 82 ohm. Not sure why they reworked the circuit and added a 25 MFD electrolytic on the wiper of the contrast pot to ground. And they grounded the other end of the pot when it should have been left floating.... A mystery.

That cap and resistor shouldn't even be there and that wire should be wrapped or soldered on a lug to pin 1 of the 12BY7.

[Davala]

showing the 25MFD cap mod they did

[old_tv_nut]

There was a recommended mod to change the CTC-5 contrast circuit to the CTC-7 version.
https://videokarma.org/showthread.ph...=ctc5+contrast

[zeno]

If the on/off /vc is a mallory easy to fix. Find Mallory KR8M & KR9M
I remember them in early 60's RCA. Others had repair kits but I never did them.
See hear https://www.ebay.com/p/2216531325

Manuals are like following bread crumbs. PCB's Golden Rods, supplaments
etc. Trouble is they always go MIA. Most shops didnt take the time to
keep there library up to snuff.

BTW nice catch & sweet cabinet !

73 Zeno
LFOD !

[Davala]

Originally Posted by old_tv_nut

There was a recommended mod to change the CTC-5 contrast circuit to the CTC-7 version.
https://videokarma.org/showthread.ph...=ctc5+contrast

Thanks for the info. Sure looks like they got it close to the proper ctc7 modification. They went with a 25MFD instead of a 50..

Thanks again,
Matt Davala

[Davala]

After a full recap I finally powered it up this afternoon. Full raster with good width and vertical. But of course I have an issue with brightness and I'm sure its that darn CTC-7 mod. Brightness is on near full at minimum and increasing it loads down the HV at max. I did verify the parts were as they should according to the mod. Even though the mod is for the contrast I assume it affects the brightness to some point. I have now 50 MFD instead of 25MFD from the wiper of the contrast to ground. The previous tech only added a 25 while the CTC 7 mod calls for 50mfd.

I'll pull the chassis again and do some measurements of the brightness circuit as well as the contrast circuit. If everything checks ok I might revert back to the stock CTC-5 contrast circuit and see what effect it has on brightness and go on troubleshooting from there.

Any other ideas? BTW agc and sync were out of wack but I'm sure thats because the video output was being driven really hard.
It also seems that DHR4863 was unable to fix his CTC-5 issue. Unfortunately it sounds exactly like my issue....
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Matt Davala

[damen]

Have you followed the instructions in the service manual for setting the screens and background controls? The directions are different than those for sets that have a service switch.

[Davala]

Originally Posted by damen

Have you followed the instructions in the service manual for setting the screens and background controls? The directions are different than those for sets that have a service switch.

Thanks for the reply. I did go through the manual and got the brightness level settled in. Interesting relationship between the background and screen controls.

Setting convergence on this thing is a pain! I accidentally pushed a coil trimmer screw for one of the convergence settings past the threads. Watching the screen and twisting I didn't realize it was at the bottom of the threads already. Got to pull the chassis for that.

No color coming through. I adjusted the killer control but saw no change to the bars. I'll see what I can tweak from the topside but I'm assuming I'll be pulling the chassis for that too.

Tuner, IF, video, audio and the deflection all seem to be working. Darn chroma!

Thanks guys,
Matt Davala

[Davala]

Wish I was watching this in color! Vertical hold requires about half a dozen adjustments until it warms then its stable.

The tubes in the chroma section feel pretty darn hot. I think I remember that board looking toasty. I'll check resistors there tomorrow.

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Matt Davala

[Yamamaya42]

Originally Posted by Davala

Wish I was watching this in color! Vertical hold requires about half a dozen adjustments until it warms then its stable.

The tubes in the chroma section feel pretty darn hot. I think I remember that board looking toasty. I'll check resistors there tomorrow.

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Matt Davala

my precious color! that filthy hobit stole my precious color!

[Yamamaya42]

“Vertical hold requires about half a dozen adjustments until it warms then its stable.”

Looking at the schematic, one can see why, at some point between the CTC 11-> 15, RCA added a voltage dependent resistor into the mix, this no doubt made it more stable and robust and less susceptible to instability as the parts aged.

[Penthode]

In my Whitby I had a lot of problems with vertical sweep. The vertical hold drift I fixed by changing resistors. I found found the original very temperature sensitive.