Montgomery Ward 1987 13" color tv (bad horizontal )

[liammc00]

¹I recently got this TV for $1 at antique store and it dose power up but has horizontal problem. I have checked the caps in horizontal drive circuit. Cap C507 is 47mfd at 35v tested at 8.08 ohms so it's bad and cap C506 tested with litter higher then it should the rest were in spec. The picture below will show you the symptom I'm have with this TV. Other then horizontal it seems to work fine. I have to order some caps before I can continue with the repair on this TV. the tv seems to be a low hour set.

[old_coot88]

Sure looks like the yoke. But get some more opinions before sinking any $$ into it.

[zeno]

Thats a weird symptom. Never seen a yoke short in a modern set
& give a key stone pattern. Bad yokes are super rare on solid state
sets. Out of thousands I may have seen 10 & most were on GE's.
I would look at the power supply 1st. A good chassis pix will
show who built it & maybe a few more ideas. A model ## too !

73 Zeno
LFOD !

[liammc00]

Originally Posted by zeno

Thats a weird symptom. Never seen a yoke short in a modern set
& give a key stone pattern. Bad yokes are super rare on solid state
sets. Out of thousands I may have seen 10 & most were on GE's.
I would look at the power supply 1st. A good chassis pix will
show who built it & maybe a few more ideas. A model ## too !

73 Zeno
LFOD !

The OEM is Sharp

[dishdude]

Looks like a Sharp and agreed it's something in the power supply.

[damen]

I vote yoke

[damen]

Remove yoke and look at the windings where the rubber wedges rest on the coils.

[old_coot88]

With a pic tuned in, does the keystone effect slowly "crawl" up (or down) the screen? Or is it always stationary whether there's a pic tuned in or not?

[zeno]

Yup its a Sharp & IIRC it uses an SCR in the power supply. That
area would give some strange symptoms.

[old_coot88]

This'n will be an interesting case study for sure. I never seen a bad yoke in a SS set before either (but plenty of tube type). If it ain't the yoke, what is causing the horz sweep to be "modulated" by the vert sawtooth?

If it turns out to be the yoke, it'll be the first (SS) one for me.

[zeno]

Originally Posted by old_coot88

This'n will be an interesting case study for sure. I never seen a bad yoke in a SS set before either (but plenty of tube type). If it ain't the yoke, what is causing the horz sweep to be "modulated" by the vert sawtooth?

If it turns out to be the yoke, it'll be the first (SS) one for me.

What I remember a FBT winding was in series with the SCR to turn it off.
The whole thing was timed at hoz rate. There was also a small IC that controled it. That needed a hoz pulse & ran on a FBT supplied B+.
RCA did a similar thing & when the main filter cap opened it looked
like a Christmas tree. Quite distinctive..
Lets have the model ## so I can pull the Sams

73 Zeno
LFOD !

[liammc00]

Originally Posted by zeno

What I remember a FBT winding was in series with the SCR to turn it off.
The whole thing was timed at hoz rate. There was also a small IC that controled it. That needed a hoz pulse & ran on a FBT supplied B+.
RCA did a similar thing & when the main filter cap opened it looked
like a Christmas tree. Quite distinctive..
Lets have the model ## so I can pull the Sams

73 Zeno
LFOD !

The model is JSJ12227

[zeno]

Not listed in Sams. If there is a Sams set in your area ( library etc. )
you can look for similar Sharps in that time frame. Bring the number
off the jungle & regulator IC's also the flyback ( rtrnf #### ) &
you will get very close.

73 Zeno
LFOD !

[liammc00]

You guys were right the yoke is bad. The yoke had shorted windings doto the varnish being bad. so I'm going to rob it for parts. Let it RIP.