Ge kd chassis 18" color has low boost voltage

[jeffilm]

I thought the crt was almost dead. I checked the crt screen voltages. They were all around 390- 400v. They should be about 670v. No brightness at all. If you crank up the color level you will see an image. Checked the CRT with a Sencore CR70, shows very good emissions on all guns. B&K 467 shows same results. Shows in the red on a Sencore CR7000. No cutoff adjustable at all. (I think this tester is too sensitive for TV CRT's.) Designed more for Video Game Displays. Still have to remove the PVA material from the CRT. It's one of the worst I've seen! Any idea's for the low boost? It's supposed to be 970V. Its only 400V I did change the selenium boot rectifier. Could something be loading it down? I disconnected the vertical circuit from the boost. Still the same. I'm going to do the same with the CRT screen circuit, maybe an issue there. I think it's also what is causing the somewhat low vertical deflection. Doesn't quite fill the screen...Jeff

[DavGoodlin]

If you have full horz deflection, good- you are on the right track. Boost supply has extremely low current capability, so even a leaky capacitor of any kind can do this.

Another possible cause is an open (was it .068?) capacitor on the boost line. Scope it if you can to confirm.

If you have a schematic, sams 959 IIRC, look for the boost tie points and disconnect each one, including vertical to see if voltage rises much. It is possible you have another bad boost rectifier.