RCA 21CT55 B8802897 is Alive!

[Tomcomm]

I have this continuing problem with my 21CT55 after a year of operation.With ext video input from the DVE test DVD at blacker-then-black video level input and the contrast and brightness controls fully CCW, I observe a uniform, non-raster, very low-level white glow over the entire screen. This is only obvious in a totally dark lab on the RCA but not on the Sony monitors operating on the same video.

During critical PQ evaluation comparisons with the Sony with no room lights, this glow detracts from the absolute black of the RCA on demo DVE's video relative to the Sony. This is disturbing to me since I never watch LCD TV and suspect my RCA crt's black presentation is similar...yuk!

What to do?? I've tried a few diagnostics:

(1) I determined the 21FBP22A is driven well into cutoff by at least 120vdc.
Besides, the glow is not scan-line defined as if it was going thru gun optics.

(2) By under-scanning the crt with misadjusting the vertical linearity control,
the glow is confined crudely to the raster area of the crt but totally out of
focus. So its effected by the deflection yoke but not the gun optics?

(3) Could this be caused by secundary emmission from the gun elements?

(4) Could it be caused by X-RAY excitation of the gun elements? I am running an ultor of 30kv. The 21FBP22 is rated for 27.5kv so I reduced it to a min of 22.5kv with absolutely no change in the glow intensity.

(5) How about a small air leak? No violet glow in the gun assembly.

(6) I pulled off the crt socket and turned the power on and let the ultor come up. No screen glow so I pressed the crt socket back on. No immediate glow as the crt heaters came up to temp, still no glow. After about 3min running, a glow was barely noticeable. It got progressively brighter until after about 10 min it was at maximum. I directed a fan at the crt neck attempting to cool it but it made no difference.

Question: Is this low level glow I have on my 21FBP22A a common phenomenon observed on many early roundys but only noticed on very dark scenes in totally dark rooms? Since I have only one operational roundy and have not observed another roundy in 30yrs I have no way of finding out. I would be very grateful for any worthwhile replys regarding the cause of this glow and the prevalence of this abnormality in other forum member's roundys.
......Tom

[roundscreen]

Originally Posted by Tomcomm

I have this continuing problem with my 21CT55 after a year of operation.With ext video input from the DVE test DVD at blacker-then-black video level input and the contrast and brightness controls fully CCW, I observe a uniform, non-raster, very low-level white glow over the entire screen. This is only obvious in a totally dark lab on the RCA but not on the Sony monitors operating on the same video.

During critical PQ evaluation comparisons with the Sony with no room lights, this glow detracts from the absolute black of the RCA on demo DVE's video relative to the Sony. This is disturbing to me since I never watch LCD TV and suspect my RCA crt's black presentation is similar...yuk!

What to do?? I've tried a few diagnostics:

(1) I determined the 21FBP22A is driven well into cutoff by at least 120vdc.
Besides, the glow is not scan-line defined as if it was going thru gun optics.

(2) By under-scanning the crt with misadjusting the vertical linearity control,
the glow is confined crudely to the raster area of the crt but totally out of
focus. So its effected by the deflection yoke but not the gun optics?

(3) Could this be caused by secundary emmission from the gun elements?

(4) Could it be caused by X-RAY excitation of the gun elements? I am running an ultor of 30kv. The 21FBP22 is rated for 27.5kv so I reduced it to a min of 22.5kv with absolutely no change in the glow intensity.

(5) How about a small air leak? No violet glow in the gun assembly.

(6) I pulled off the crt socket and turned the power on and let the ultor come up. No screen glow so I pressed the crt socket back on. No immediate glow as the crt heaters came up to temp, still no glow. After about 3min running, a glow was barely noticeable. It got progressively brighter until after about 10 min it was at maximum. I directed a fan at the crt neck attempting to cool it but it made no difference.

Question: Is this low level glow I have on my 21FBP22A a common phenomenon observed on many early roundys but only noticed on very dark scenes in totally dark rooms? Since I have only one operational roundy and have not observed another roundy in 30yrs I have no way of finding out. I would be very grateful for any worthwhile replys regarding the cause of this glow and the prevalence of this abnormality in other forum member's roundys.
Maybe Scottie is knowledgeable? Anyone know him personally?......Tom

I have seen the glow on modern set's and it was the screen voltage set to high, But I would think you would see retrace. Try turning down the screen controls and see if your problem goes away. I have never seen this on my round color sets and I use them almost every day.
Ed