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Zenith SM276759 - n00b to repairs..

Hi - please don't flame me *too* much, as I'm still teaching myself on
the fly - and have done a good bit of mostly confusing research. All
I have available to use is a multimeter, which I've done continuity
tests with on most of the major resistors and capacitors. Uncertain
about how to test caps properly without replacements or the like.

TV is a 27" built around 1994.

Has screen issues - is solid green with rescan lines (I think they're
called) running down it.

On screen display and menu shows up still, ironically, but anything
else only provides the faintest ghosting.

Messed with the color pots - got expected result; more green red or
blue and whatnot, no change to rescan.

Adjusting G2 all the way down gives extremely dark, extremely
oversaturated image.

Would appreciate whatever idiot-level help I can get; this stuff is a
lot like Linux; you've gotta know 15 things just to learn one new
aspect.
 
N

nipperchipper

Jan 1, 1970
0
1994 to 1997 Zenith were famous for having picture tubes that shorted and
what you describe is that symptom
 
B

Brittany Martin

Jan 1, 1970
0
Hi - please don't flame me *too* much, as I'm still teaching myself on
the fly - and have done a good bit of mostly confusing research.

I'll flame you as much as I goddamn well please.
If your teaching yourself electronics, then get a Radio Shack
10930923409234 in 1 electronics kit.

Don't just start fucking around inside a T.V., there are high voltages
inside especially around the tube which will throw your balls to the
wall.
All
I have available to use is a multimeter, which I've done continuity
tests with on most of the major resistors and capacitors. Uncertain
about how to test caps properly without replacements or the like.

TV is a 27" built around 1994.
Many Tee Vees don't last 13 years so consider yourself and your dick
lucky.
Has screen issues - is solid green with rescan lines (I think they're
called) running down it.

On screen display and menu shows up still, ironically, but anything
else only provides the faintest ghosting.

Messed with the color pots - got expected result; more green red or
blue and whatnot, no change to rescan.

Now you'll have to throw away the T.V.. It's a bitch to get those
color pot settings back they way there were.
 
I'll flame you as much as I goddamn well please.
If your teaching yourself electronics, then get a Radio Shack
10930923409234 in 1 electronics kit.

Don't just start fucking around inside a T.V., there are high voltages
inside especially around the tube which will throw your balls to the
wall.



Many Tee Vees don't last 13 years so consider yourself and your dick
lucky.




Now you'll have to throw away the T.V.. It's a bitch to get those
color pot settings back they way there were.

Heh...neither polite nor useful. Figures.

Not teaching myself electronics so much as teaching myself
troubleshooting of complex electrical systems. Big difference - and
yes, I am aware of the voltages involved.

Is not rocket science to avoid the problem areas and use prudent
caution whilst poking around the annoying little bugger.

I marked the pots; there is no issue there. Could've adjusted those
back by sight.

So - eh. You should probably work on your diction and delivery.
Aren't gonna make many friends howling like this.

--------------------

Anyway, I looked into the shorted tube thing and am not sure how to
proceed. Presumably one can bypass the flyback with an isolation
transformer (haven't figured that one out yet but I have a rough idea)
and fix the annoyance.

I have the vague suspicion that there's a dead resistor right by the
flyback - multimeter doesn't twitch trying to put current through it.
Would a dead circuit cause something similar to a shorted out tube?
It's a fairly high octane one; about 560M. I figure it's gotta be
some sort of side-supply going to the CRT.

Appreciate the...well....*constructive* help. And I'll be careful.
Have a good bit of experience, just not with TV's.

Be well, all.
 
H

Homer J Simpson

Jan 1, 1970
0
Anyway, I looked into the shorted tube thing and am not sure how to
proceed. Presumably one can bypass the flyback with an isolation
transformer

You presume wrong.
 
A

Andy Cuffe

Jan 1, 1970
0
Anyway, I looked into the shorted tube thing and am not sure how to
proceed. Presumably one can bypass the flyback with an isolation
transformer (haven't figured that one out yet but I have a rough idea)
and fix the annoyance.

I have the vague suspicion that there's a dead resistor right by the
flyback - multimeter doesn't twitch trying to put current through it.
Would a dead circuit cause something similar to a shorted out tube?
It's a fairly high octane one; about 560M. I figure it's gotta be
some sort of side-supply going to the CRT.

Appreciate the...well....*constructive* help. And I'll be careful.
Have a good bit of experience, just not with TV's.

Be well, all.

Honestly, I wouldn't touch sets with those CRT 8 years ago and I'm
sure they haven't improved with age.

There should be a date on the CRT. If it's the original 1994 CRT,
there's no point in continuing unless you can replace the CRT.

The shorts in those CRTs are usually cathode to G1, not heater to
cathode (so an isolation transformer won't fix it). Even if you could
get rid of the short, the emission is probably too low to produce a
good picture.

Don't let the set run with a bright raster because it will blow the
power supply. Turn the screen control on the flyback down if you must
run it.

These sets used to come in dead with blown power supplies. After
fixing the power supply, you'd get anything from a poor to fair
quality picture, but eventually the CRT would short again and blow the
power supply.
Andy Cuffe

[email protected]
 
Honestly, I wouldn't touch sets with those CRT 8 years ago and I'm
sure they haven't improved with age.

There should be a date on the CRT. If it's the original 1994 CRT,
there's no point in continuing unless you can replace the CRT.

The shorts in those CRTs are usually cathode to G1, not heater to
cathode (so an isolation transformer won't fix it). Even if you could
get rid of the short, the emission is probably too low to produce a
good picture.

Don't let the set run with a bright raster because it will blow the
power supply. Turn the screen control on the flyback down if you must
run it.

These sets used to come in dead with blown power supplies. After
fixing the power supply, you'd get anything from a poor to fair
quality picture, but eventually the CRT would short again and blow the
power supply.
Andy Cuffe

[email protected]

Appreciate the clarification. Sounds like this thing is fubar - will
likely strip it for components I can use elsewhere and donate it to
the local garbage workers' job security fund. :p

Considering I got it for free, it's more than been worth acquiring, if
only for experience.
 
J

Jeroni Paul

Jan 1, 1970
0
If it has a consistent short it may be blown by discharging a charged
capacitor.
Shorts inside CRT gun can be found with multimeter unless they are
intermittent, just check continuity between all pins, only heater pins
should read some continuity. Then look inside the glass and follow the
connections to identify what is what. Some CRT manuals with pictures
on the net may help you learn the parts that make up a CRT gun. I've
seen some tubes have two pins connected inside for no apparent reason.

On the other hand you may swap the connection to the bad color with
another working one, there may be series resistors that will make that
easy. You've to identify the RGB signal pins on the CRT socket. Then
if problem persists on the same color you know it is the CRT.
 
A

Andy Cuffe

Jan 1, 1970
0
If it has a consistent short it may be blown by discharging a charged
capacitor.

That's normally true, but considering the quality of these CRTs, it's
pretty pointless. These CRTs have a manufacturing defect that causes
them to short and lose emission. Even if you could make it as good as
new it would only last a year or two.
Andy Cuffe

[email protected]
 
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