Zenith Advanced System 3 picture tube testing
 

I was hoping to test the picture tube in my moms Zenith Model SS2721H. This set was manufactured in June of 1991. The CRT is listed as a GA68ACT00X. My Sencore CR70 setup book dated 1992 does not list this CRT? I was told 12 years ago that these had junk CRT's, but I never figured out what exactly was causing the original problem of green retrace lines in the picture. We suspected it was a heater to cathode short, but I never had a good way to test it back then. Now 12 years later the set won't even power on unless I unplug the PC board that plugs onto the CRT base. My mom is still attached to the cabinet of this set. Guess I could put a flat screen in there for her. :dunno:

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:smoke:

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.

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 :boring:

73 Zeno:smoke:

you can bet that crt is junk.

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.

http://i452.photobucket.com/albums/q...psa743f9f0.jpg

What's the little slide switch on the CRT PC board for, possibly setup?
http://i452.photobucket.com/albums/q...psa5884d33.jpg

http://i452.photobucket.com/albums/q...ps6caca9c1.jpg

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.
http://i452.photobucket.com/albums/q...pscbc3d61a.jpg

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.
http://i452.photobucket.com/albums/q...psb42e78af.jpg

http://i452.photobucket.com/albums/q...psacd727d8.jpg

http://i452.photobucket.com/albums/q...ps06fbdbe3.jpg

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. :scratch2:

...

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:smoke:

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.

This is an SS model. Most were sold in the big stores or were
drop ins. Sometimes we could get them. If not we didnt even
get the spec sheets. Same case with S, T, ST, V & SV models.
Get the 9-*** numbers off the 2 main boards & I can see what I
have on it. It will be near identical to a regular line set.
As far as reliability goes these were decent. Some FBT's went
but completely, no raster followed by shut-down & the HOT
overheats.

...

Finally have the set at my place. Offhand I don't see those 9-*** numbers on the two boards. Are they possibly on the bottom side, or hidden by the board mounting tray?

Well duh, the board numbers were on a paper label on the inside of the cabinet.

9-959 Main
9-1075 SMPS/Sweep

Since I've gotten this thing to my place it's back to not powering on. When I push the power switch the green light on the front comes on, but the power relay does not pull in. Pushing the switch a second time won't turn the light back off. So I suspect there's something flaky with the on-off circuitry.

[edit] Actually the green light that comes on is the stereo indicator. But it won't turn off when the power switch is pushed a second time.

Pulled the PC boards out and was poking around looking for suspect capacitors. Just for the heck of it I checked the big transistor mounted on the heatsink next to the flyback transformer. Out of circuit it measures 53 ohms in both directions across the base-emitter. That can't be right, can it?

http://i452.photobucket.com/albums/q...g?t=1388426760

http://i452.photobucket.com/albums/q...g?t=1388426807

I looked through my junk stash and I have a chassis assembly, that came from a set very similar to the one you're working with. The main board is a 9-959, but the sweep is a 9-754-1.
The original problem was the set wouldn't always start the first time.
I pulled the boards and found a few solder connections that were loose.
I returned and it still wouldn't work and the owner said forget it.
If you think you could use them, P.M. me. :scratch2:

Those things fool you because of the built damper diode. If it was truly shorted, it would read 0 ohms in both directions. :sigh:

Well I was wondering about that too, but this thing shows .034 drop in both directions when my Fluke 75 is in diode check, but it also shows 53 ohms resistance in both directions. :scratch2:

Thanks for the offer, I'll think about that. At this point I'm not too sure I want to keep beating my head over this thing. Without a proper road map these solid state sets are just a major frustration to me. Life's too short and there's a lot of tube sets that are more worthy of my time. ;)

Been a while but if I remember right, that is a C2 chassis. Look around the power supply area (middle of the board on the right for weak or open capacitors. Also, look around the video jungle IC on the other board. The picture you have shown looks like a bad capacitor on the Jungle IC. It is not the large IC heading to the back. That would be the MTS IC. You virtually have to have a ESR type capacitor tester for this set. Look around the small (1 uf up to 4.7 uf) caps for liquid leaking out on the PC board. These sets were very good performers when working. The PIP modules almost always have a dozen or so dead capacitors in them. Also, look around the front of the power supply board for larger leaking capacitors. Look under the vertical IC for bad solder connections. Also, vertical fold over is going to be bad capacitors around the vertical IC. There were a lot of these sets here until Katrina got them

Thanks for all the suggestions. I'm afraid I'm not familiar with the term PIP modules?

Picture in Picture. It was a large rectangular box on the signal (left viewed from the back). Not all sets had them. I don't remember what terminals were jumpered if the module failed (disabling the PIP). If you get it running I'll look it up in my notes. The broken up picture was almost always a small capacitor by the video jungle IC. Intermittant startup/no start was a cap around the heatsink in the middle of the power supply. I liked these chassis. They can produce a great picture.

Thanks for the explanation. Is there a way to safely power the two main boards on the bench without removal of the front switch panel PC board? Any voltage test points to verify correct power supply operation?

Well I had to take the two PC boards out of the plastic tray to get at the solder side. Boy that white goo holding the connecters was a treat to remove.:rolleyes: I see at least a couple caps that have leaked electrolyte onto the video board.

http://i452.photobucket.com/albums/q...g?t=1388442015

http://i452.photobucket.com/albums/q...g?t=1388442071

http://i452.photobucket.com/albums/q...g?t=1388356006

These are the caps I've found so far on the main board that show physical signs of leakage. It looks like the Nichicon PC(M) series are the culprits, the darker blue and black ones seem OK. In several places the electrolyte has seeped through to the copper traces and made a corrosion mess. Lots of PC trace rework is in order. :sigh: I'm going to have to place a cap order.

http://i452.photobucket.com/albums/q...g?t=1388462512

http://i452.photobucket.com/albums/q...g?t=1388462397

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The transistor is either the power supply FET or the HOT.
The HOT on most mid 80's up sets have a damper diode
E-C & a resistor B-E. 99.9% dead short when they fail.
Power FET's can dead short D-S or open. The one
board Zeniths had 2 small 'lytics in the PS that caused
int dead or dead. The 2 boarders were big sets so almost
all were done in home at board level til near the end.
For the control board it helps to have one of those 3 foot
long xelite 1/4 drivers. I still got mine but you will have to
pull it out of my cold dead hands.
I will look later today for the manual.

73 Zeno:smoke:

I dont have the Sams so I pulled a similar one for a J line set.
Its got some circles that may help also. Keep in mind this
is part of the same family & some things may NOT be the
same.

The transistor is the HOT not to worry.
Power supply caps are C3407, 3440, & 3408 start here.
Jungle IC, IC2301 caps in hoz C2726 also circled R2704 & R2752 & the IC
The only VCC I see for the jungle is 8 volts at pin 42.
The switch at CRT is a service switch.

The other problem is you have a green screen. This set has AKB
that automaticly adjusts grey scale. No adjustments. Odds are
the R & B are down so you may have to rejuvenate..........
So dont spend much on it yet.

73 Zeno:smoke:

Thanks, zeno.
Yeah, I realize replacing all the bad caps could be in vein if the CRT has issues. Although I doubt I'll have over $10 invested in caps, plus a few hours of my time. I actually thought the picture had a decent gray scale last time it was on. My pictures made it look more green than in person. Oh, by the way - does that Sams give the pin-out for the CRT? I'd still like to verify I was checking it correctly.

Pin out same as I gave you. K voltages a little higher than norm,
130-140 V. Ive got some tricks if the grey scale is off, we shall see.
Try a life test on CRT also, if checker doesnt have it just
kill the filament & watch the meters. I think u have a CR70 , IIRC
it has it. Time for a beer:beer:

73 Zeno:smoke:

Many of the HOTs that contained built-in damper diodes also had a 50-100 ohm internal resistor across the B-E junction. I'm sure this is what you are seeing here.

If it was not blowing fuses and generating HV, the HOT is likely just fine.

Finally today I got around to replacing 31 leaky capacitors, and it seems to have done wonders. Basically the picture looks very good to me, and no sign of those green retrace lines I recall seeing 12 years ago. The only very minor issue I see is some subtle shading down in the lower right corner. It's hardly noticeable unless there's a solid color on the screen, but then again sometimes it looks fine then too. I can see it best on the two b&w pictures below. I want to thank everyone for helping out with the suggestions on getting this set going. :thmbsp:

http://i452.photobucket.com/albums/q...g?t=1389922054

http://i452.photobucket.com/albums/q...g?t=1389838554

http://i452.photobucket.com/albums/q...g?t=1389922239

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http://i452.photobucket.com/albums/q...g?t=1389922377

http://i452.photobucket.com/albums/q...g?t=1389910218

Nice work ! Nothing wrong with that CRT, the purity is
off a little on the bottom right, see if a little magnet on
tape fell off the CRT bell & is laying on the bottom.
Beyond that I would leave well enuf alone.

73 Zeno:smoke:

Good job fixing that television you saved it from the scrap yard . That's always good when People care to fix a television and not buy that Chinese flat panel junk that breaks after 3 years or right after the warranty from the manufacturer .I always thought Zenith was a very High End set , But I also Like Sony Trinitrons Televisions . I got A 40 Inch set for free from a guy in Waukegan .Illinois that Didn't want to fix it . I need the famous Mz3001d chips in her . But the set is working Not and has been turning on and not giving me any trouble knock on wood .I have the chips and if needed I can replace them now .

I've started to notice some light-dark horizontal streaking in the picture. Also some light green retrace lines are visible when the set is first turned on, as well as the screen collapses to a green dot when powered down. So it seems there may be some heater to cathode leakage after all. So far I haven't been able to capture the green retrace lines on camera, only the light-dark streaks. What do you guys think?

http://i452.photobucket.com/albums/q...g?t=1390533516

http://i452.photobucket.com/albums/q...g?t=1390447248

You have directv hooked up to it . My Sony television will do the same thing too . Try a dvd player and see how the picture is . Im betting it one of your coax cables causing that bad picture or something in the tuner getting the signal . Check your cables

Actually it is a DVD player with separate RCA audio and video cables hooked to the TV.

An odd symptom. If it comes & goes try light tapping
of the CRT neck & see if it flashes. Can also swap the
transistors around & see what happens. Also run your tester
up a little on the filaments & see if it smokes out leakage.
Try it at 8V. These sets did some strange things when the
CRT's were bad.............

73 Zeno:smoke:

Whatever it is it likes to manifest itself on mostly light blue screens. The moire effect makes it a little tough to see below. The color rendering looks great to me. I'll try testing the CRT again later.

http://i452.photobucket.com/albums/q...g?t=1390590033

http://i452.photobucket.com/albums/q...g?t=1390547335

More pictures...

http://i452.photobucket.com/albums/q...ps91760968.jpg

http://i452.photobucket.com/albums/q...ps178f8654.jpg

http://i452.photobucket.com/albums/q...ps505032fb.jpg

http://i452.photobucket.com/albums/q...ps814fa621.jpg

http://i452.photobucket.com/albums/q...ps15b27b4a.jpg

http://i452.photobucket.com/albums/q...ps4ac0770b.jpg

http://i452.photobucket.com/albums/q...psdd1916eb.jpg

http://i452.photobucket.com/albums/q...psdbda94d2.jpg

The minor purity issue really isn't showing too badly on a red raster. It's a non-issue from where I'm sitting. Usually the red raster is the one to exploit 'impurities' in the crt setup.
One of my neighbors still uses this exact type of system 3 on cable. I don't recall there being any problems with it. I believe it was a 1992 model.

You caught an awesome example of moire, best ive ever seen.
The Zenith folks described it as looking like a finger print
when we first encountered it on the old 14" tube jobs. We
had someone with a new 14" Zenith we sold bring one in for it.
After that it could be spotted in other sets even much older
ones.
One things for sure, all 3 guns have great emission. Like I
said these jugs did odd things when bad, you couldnt glance
at them & say "bad CRT" a lot of times. Sometimes it was like
someone was in back changing the grey scale slowly so
you couldnt do a set-up. Good one minute & bad the next but
not by much.
For the purity take a little magnet from a junker, put it on
the corner of the bell. Slide it in & out & rotate it for good
purity, works most the time.

73 Zeno