Interesting hack repair on a CTC-5, your thoughts?

[roundscreen]

Check r 601, c601 and the horz drive voltage going to the brightness control.
I take it the horz drive voltage must be there cause you have a raster.
I took the part location numbers from the rca field service guide so you should be able to find them.
I have seen a write up on this problem but never had the problem with my set's.
Ed

[drh4683]

Interesting. I'll have to keep checking around. If I turn down the brightness control, the contrast and turn all the screens and background controls fully CCW, the raster is still present, a drab green image is what appears, slightly below average viewing brightness.
I worked on a CTC-19 a couple years ago that had little control of brightness that I couldn't cut off as well. That set turned out to have a completely hacked up B-boost circuit with parts that didn't reflect any schematics. I changed it all back to factory and it worked perfect again.

[roundscreen]

Originally Posted by drh4683

Interesting. I'll have to keep checking around. If I turn down the brightness control, the contrast and turn all the screens and background controls fully CCW, the raster is still present, a drab green image is what appears, slightly below average viewing brightness.
I worked on a CTC-19 a couple years ago that had little control of brightness that I couldn't cut off as well. That set turned out to have a completely hacked up B-boost circuit with parts that didn't reflect any schematics. I changed it all back to factory and it worked perfect again.

This sounds like a problem with the grid voltages going to the crt. OR you may be right about the screen voltage being to high
Snoop around the 12AT7's and check voltages,Caps, Resistors and the coils.
The green gun seems to be the brightest color on the 21axp crt for some reason so that may be why you see the green stand out with everything cut off.
Still, The drab green image may be a clue as to what is going on too.
My favorite hack job is when they would turn the high voltage all the way up when the set had a weak crt or there was not enough horz width.
Of course I would see there kids watching the dam thing to boot
The next thing would be when they put in a 10 amp fuse in a circuit that takes a 1 amp fuse. . Man , Techs did some strange things back then.
Ed

[grimer]

---

[Ampico-kid]

Originally Posted by grimer

I have a question,does the hack/mod actually improve the picture?

A little over a year ago I was working on my RCA CTC5 Aldrich and was having a heck of a time with the brightness and contrast controls. They seemed to interact with each other and neither worked as you would expect it should. bgadow (Bryan) came up with an article discussing a factory modification to correct this problem. I performed the fairly simple modification and presto....the brightness and contrast worked 100% normal. Yes...it improved the picture greatly!!

I don't know what the RCA engineers were thinking when they designed the set? It just didn't work right. But with the modification all is well.
Bob

[Robert Grant]

Originally Posted by Ampico-kid

A little over a year ago I was working on my RCA CTC5 Aldrich and was having a heck of a time with the brightness and contrast controls. They seemed to interact with each other and neither worked as you would expect it should. bgadow (Bryan) came up with an article discussing a factory modification to correct this problem. I performed the fairly simple modification and presto....the brightness and contrast worked 100% normal. Yes...it improved the picture greatly!!

I don't know what the RCA engineers were thinking when they designed the set? It just didn't work right. But with the modification all is well.
Bob

Perhaps they were thinking....

Let's see, how can we get the price below $ 500....cut wideband I demodulation......cheapen the cabinet...Hmmm, electrolytics aint cheap, any way we can get that one out of the contrast circuit???

I wonder of this omission was common to all CTC-5s, just the less expensive "Super" models, or unique to the least-expensive Aldrich