Another Zenith - 23XC36 - blown tubes - Videokarma.org TV - Video

RetroHacker · #1 12-07-2005, 10:37 PM

Well, getting further into things in the garage, I did a little poking around in this Zenith console, it's a 23XC36. The sound works, but no HV. As it warms up, the sound comes in first, crackley due to a dirty control, and a whine like deflection whine, then a whisling whine - sounds a lot like a tea kettle. The HOT is glowing an unusual purlple-ey blue. So... I pulled out the HOT and the tube next to it, and both appear gassy. The horizontal output tube (6JS6) is a little browned around the very base, and the getter shows a bit of rainbow-y reddish ringing with a little white, although I don't think that it's gassy enough to have turned the whole getter white. The nearby tube, a 6HS5, is totally cooked. According to the tube chart, it's being used as a voltage regulator. The whole glass is golden-brown, and the getter is largely reddish. So... something caused these things to draw way too much current. The flyback actually looks pretty good, no scorching, although that doesn't mean much. I haven't had time to pull the chassis or do any further detective work on it, this is another one of those things where I figured I'd get some insight on the problem before spending a lot of time - time I don't have. I really need to pull out the chassis and do some thorough cleaning, this thing is filthy!

Hmm, it's weird - it seems every color set I find has some HV problem, where all my previous sets were black and white sets with low voltage problems, or just bad caps in vertical circuits and stuff. With the old B&W sets I normally didn't have to deal with the HV - I was replacing electrolytics and coupling caps and rebuilding vertical circuits, HV just always worked. Here with the color sets, the HV sections seem to be the weak point, which is annoying, because it's the part that I don't understand as well... Sure, I know _how_ it works, but it's still hard for me to put my finger on specific symptoms.

-Ian

Adam · #2 12-08-2005, 12:20 AM

whisling whine - sounds a lot like a tea kettle.

I heard that sound on an early Magnavox color I was working on, and about a minute later the flyback actually started to melt!

I think the sound was the coating in the flyback boiling?

RetroHacker · #3 12-08-2005, 08:52 AM

Well, I didn't leave it running long enough to find out what else might happen... But I certainally hope that the flyback is serviceable. I just assumed that the sound was caused by the plates oscillating in the gassy tubes.

-Ian

Chad Hauris · #4 12-08-2005, 06:05 PM

Most important check is for negative grid bias voltage on HO tube, if there is none or it's low you don't have enough, or you have no, oscillator signal.

wa2ise · #5 12-08-2005, 06:14 PM

Quote:

Originally Posted by RetroHacker

Hmm, it's weird - it seems every color set I find has some HV problem, where all my previous sets were black and white sets with low voltage problems, or just bad caps in vertical circuits and stuff. With the old B&W sets I normally didn't have to deal with the HV - I was replacing electrolytics and coupling caps and rebuilding vertical circuits, HV just always worked. Here with the color sets, the HV sections seem to be the weak point
-Ian

Remember that the HV section in a color set has to work much harder than that in a B&W set. With the shadow mask, about 1/4 of the electrons from each gun actually hits phosper, the rest hit the mask and are wasted. To a first order approximation, the HV consumes 4 times as much power. And if the red, green and blue phospers are not as efficient as phospers in a B&W tube, it gets worse.

That coupled with manufacturers cutting cost to the bone would do it.