Zenith Advanced System 3 picture tube testing

[zeno]

To test the jug use the universal adapter & the "common"
settings ( dont remember what they were). Green & retrace
could be H-GK short, tap neck wile running & see if it
flashes. Can also hang a meter on GK & pull socket while running.
Normal K voltage abt 100V - 130V, if low with socket on but normal
off its the tube.
Set can shut down with excessive beam current BUT it must warm
up 1st. Can be caused by:
Excessive G2 voltage
loss of 200 V supply for the R,G, & B transistors.
A dead shorted H-K may also.
Sometimes these sets would come in with the power supply out.
Fixed them, looked OK then a few weeks later back again.
The CRT's arced & blew the supply. Most I saw bad were from
low emission or drifting grey scale followed by shorts & arcs.
It also affected cheap models more so I would guess they put
a better grade in the high end sets ( they deny that).

73 Zeno

[Kevin Kuehn]

Originally Posted by zeno

To test the jug use the universal adapter & the "common"
settings ( dont remember what they were). Green & retrace
could be H-GK short, tap neck wile running & see if it
flashes. Can also hang a meter on GK & pull socket while running.
Normal K voltage abt 100V - 130V, if low with socket on but normal
off its the tube.

Thanks for the suggestions. My problem is I don't have any service info for this set, and I can't find specs and pinout for this CRT.

[zeno]

You can usually see the filament pins then trace out the others.
Just put the 2 F clips on first & be sure it lights before going on.

Here is the pinout for a mid 80's Zenith 27" jug.
Odds are its the same.
F pin 9
F 10
KR 8
KB 11
KG 6
G-1 5
G-2 7
Focus 1
After I wake up I will see if I got a manual

73 Zeno

[rcaman]

you can bet that crt is junk.

[Kevin Kuehn]

I went over to moms tonight with my CR 70 in hand. I think I figured out the CRT pinout, and it actually seemed like all three guns checked OK for HK shorts. Cutoff and emission seems OK too. Took a few pictures of the set.



What's the little slide switch on the CRT PC board for, possibly setup?




I finally got the set to come on with the CRT board plugged in. This is with no input signal. Normal background hiss with the volume up.


These next three pictures are with a DVD Player hooked to a A/V inputs. I can see a vague image moving around accompanied by a loud hissing-scratching- popping sound from the speakers, with the volume all the way down. It almost seems like the video is modulating the audio power supply. Anyone recognize these symptoms? This is not what I remember this set doing 12 years ago when I had it on. But my folks had two of these same sets(one upstairs, one down), so it's possible I was working with the other one at the time.






I'm about to drag this set up out of moms basement and back to my place. It's a real pain trouble shooting it over there away from my shop. If nothing else it needs to come out of there so I can dispose of it. But it sure would be nice to get to the bottom of this problem before sending if off to the recyclers.

[andy]

...

[zeno]

Originally Posted by andy

Not so fast. Zenith CRTs didn't go completely bad until 1993. The earlier 27" ones were hit or miss, but many were fine. Anything from 1993, or 1994 is definitely bad.

I second that. Thats a 2 board set & they were not near as bad.
It looks like the FBT is breaking down. When you get it home unhook
the SPKRS & use a paper towel tube to listen for arcing.

73 Zeno

[Kevin Kuehn]

Originally Posted by zeno

It looks like the FBT is breaking down. When you get it home unhook
the SPKRS & use a paper towel tube to listen for arcing.

73 Zeno

Would checking the HV verify if this is the case? I searched the Sams website but nothing comes up using the sets model number. Did Sams not provide service info for these era Zeniths? I'm more less curious because I doubt this thing is worth investing in the paperwork. My fear is that when I fix one problem, another issue will soon surface.