Quote:
Originally Posted by irext
From the youtube video it looks like a low emission CRT to me. It has that silvery look on highlights. If the CRT tester you are getting has a rejuvenate function it might be worth a go. I've found that older B&W tubes rejuvenate quite well and usually last for a good amount of time. Colour tubes not so good.
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I went through and checked all of the resistors in the AGC and video output circuits and found the 390K was measuring about 430K and the 15M was measuring closer to 30M. I replaced the 390K, and put back the 15M (since I don't have anything that high on hand), and in so doing it seems to have developed a new problem. There's now this pulsing effect in both the video and audio that isn't affected by tuning or any of the controls.
Still absolutely no effect from the AGC control on the picture. The schematic says the control is 750K, but it tests closer to 475K. However the wiper travel is smooth and resistance is correct all the way around and I'm not finding anything out of the ordinary at all.
Now for the good news. I tested the CRT on the CR70 and sure enough, no cutoff and tested at about 2 in the bad range. Irext, I took your advice and did a rejuvenation, and just like that I have cutoff and emissions in the 10-11 in the green. And now the picture is indeed brighter, though the life test drops like a stone. Is this effect typically permanent or have I just given it an adrenaline shot that will wear off?
This was how it tested after the rejuv, last night. I left it connected to the CR70 and tried it again this morning and while cold it started at about 2 in the bad and slowly creeped up to about 9-10 in the good range over about 3-4 minutes. Still had cutoff control, but not as good as in the video. Is there ever any benefit to hitting it again with rejuv/auto restore or is that just asking for trouble?
https://youtu.be/tGNYEsj6CGw
Not sure what's going on now with this pulsing/noise. Here's the new, brighter picture with that annoying new problem.
https://youtu.be/GSc_GAQxrsI
FK