Zenith SS2712VK9 Horizontal "Breathing"

[Bill S]

Have a Zenith SS2712VK9 with a little problem with horizontal
size stability. The sides of the picture intermittantly move
in and out a bit. Vertical is stable, tuning and sound are
okay, etc. Supplies and horizontal drive signal appear to
be solid and stable. I am suspecting something in the pin
correction circuitry. Anyone have a schematic or tips they
are willing to share? TIA.

 

[[email protected]]

How about posting the chassis series, or module number, year of
manufacture?

 

[Edd Whatley]

I tend to define “breathing” as a uniform, repetitional slow tim
constant of change, while what you describe is random in it
occurrences.
Well with the SS we know it’s a sheltered model and with the 27 it ha
a 27 inch pic tube,
and with a 12 suffix its at the very bottom of the design/feature
line or a table model. But we still don’t know the manufacture ag
…listed on the back model tag…. or the sets module complement. Bu
anyhow, going on in the blind. Have you observed a still/stable/fixate
enough pattern to ascertain if that hoz compression is squeezing i
equally from both sides. Or is there is a coke bottle type of sid
compression, with the most compression being in the center and bowin
in less at top and bottom. If its the first symptom, the overall ho
drive/sweep level is changing. If the latter you are experiencing
cutting in and out of the pincushion correction circuitry.
I suspicion that you are starting to experience an intermittency o
connection in a solder joint on a hoz or pin ckt component tha
inherently runs quite warm or carries a high pulsed current level thr
its path, or is in the close proximity of another warm runnin
component. What I might suggest is getting an ~ ¼-3/8 in dia soli
plastic rod that is ~ 1 ft long ( Venetian blind adjustment rod
etc…[let your wife figure that one out…-12 in shorter rod]) . This wil
provide a protective/insulated rod to tap upon suspected component
with. The set is operational with the back off and a stable stil
picture from a cable bulletin board type of channel or the stable sel
produced logo from a DVD player is utilized. Observing the reflectio
on a frontally placed mirror , components in the hoz sweep an
pincushion circuit are light/moderately tapped while the pattern i
observed for compression to pinpoint a touchy component/ connection.
Positioning is referenced while viewing from the back of the set.
In most all Zeniths, the hoz sweep area and its components are at th
right rear area, working forward. The chassis/module with the mos
troublesome pin circuitry is to the right front corner where there is
troublesome pair, of a hot running pincushion diode and a verticall
mounted pincushion coil.
Lastly, and you do know *not* to French Kiss the very well insulate
red high voltage wire going up to the picture tubes top insulated ulto
connection from the high voltage transformer don’t you , otherwise yo
will be safe by your using the isolation and distancing provided wit
the acrylic rod.
If detected, a touchy part will justify an almost microscopi
inspection of its solder connections for it being almost floatin
within its solder connection blob…thus necessitating a rosin fluxin
and a reflow soldering with fresh solder.
Standing by
73’s de Ed

 

[Bill S]

For those who asked for more information, the "service number"
is SS2712VK9, serial number 091-25500260, manufactured in December
1990, and shows a "module replacement number" 9-896. There is
no information identifiable as a "chassis number" that I can see
anywhere.

 

[Bill S]

I tend to define “breathing” as a uniform, repetitional slow time
constant of change, while what you describe is random in its
occurrences.

Had to choose one word for short title description, and hopefully
described it better in the body. Could have said "jitter", but not
sure if that fits either.

Well with the SS we know it’s a sheltered model and with the 27 it has
a 27 inch pic tube, and with a 12 suffix its at the very bottom of the
design/features line or a table model.

Actually, it's a rather nice floor model with stereo I/O and glass
doors and shelves in the bottom for VCR or component audio. I thought
the "service number" SS2712VK9 would be sufficient, but if it helps
serial number is 091-25500260, manufactured December 1990, "module
replacement number" 9-896. Is the module replacement number what
passes for a chassis number in Zenith circles?

But anyhow, going on in the blind. Have you observed a still/stable/
fixated enough pattern to ascertain if that hoz compression is squeezing
in equally from both sides. Or is there is a coke bottle type of side
compression, with the most compression being in the center and bowing
in less at top and bottom.

It is changing about the same on both sides, and the amount of pin
correction does not appear to be changing. As near as I can tell
without a schematic, it appears to use the single big diode modulator
pincushion setup. But it also has a big NP elctrolytic that most
makers do not use. Maybe I start there since I can read the value
and happen to have one handy. Some of the other parts like the big
safety cap, for example, just have house numbers so I am not totally
sure what to use for sub. I hate when they do that.

I suspicion that you are starting to experience an intermittency of
connection in a solder joint on a hoz or pin ckt component that
inherently runs quite warm or carries a high pulsed current level thru
its path, or is in the close proximity of another warm running
component. What I might suggest is getting an ~ ¼-3/8 in dia solid
plastic rod that is ~ 1 ft long

Horizontal drive looks plenty big and doesn't seem to change when it
is acting up, and the HOT doesn't get excessively warm, so I think it
is being switched hard enough and the problem is somewhere downstream.

I have a small paint brush with plastic handle that I use for both
cleaning and tapping, and nothing seems sensitive. I've inspected
the soldering pretty close and sucked off and resoldered anything that
looked questionable plus a few that didn't. Replaced on principle a
cap that had leaked a bit even though it checked good. So far nothing
has affected the problem.

The chassis/module with the most troublesome pin circuitry is to the
right front corner where there is a troublesome pair, of a hot running
pincushion diode and a vertically mounted pincushion coil.

Roger the big diode and coil. I'll give them the third degree...

And about the big safety cap that only has a Zenith number on it -
I'm reading about 4700 pF and ESR looks reasonable. I'm guessing it
might be a 1600V polypropylene if I have to make a stab at a real
world part. Does that sound right?

Lastly, and you do know *not* to French Kiss the very well insulated
red high voltage wire going up to the picture tubes top insulated ultor
connection from the high voltage transformer don’t you

The big red wire has mostly not been a problem for me, but I am good
at finding pinholes in the smaller white focus wire (bszzzht!) ;-)

Thanks.

 

[[email protected]]

When you say jitter, do you mean the edges look like a sawtooth?
If yes, then replace the 22uf capacitor right next to the jungle ic on
the 9v line.

If the chassis has the metal can shields in the power supply, there are
three or so bad capacitors in there.

A good ESR meter will find the bad ones easily.

 

[Bill S]

When you say jitter, do you mean the edges look like a sawtooth?
If yes, then replace the 22uf capacitor right next to the jungle ic on
the 9v line.

No, jitter was the word I *didn't* choose for the title, and what
you describe I believe is called "piecrust", and no it isn't doing
that, it just changes a little in width and not in a periodic way.

If the chassis has the metal can shields in the power supply, there are
three or so bad capacitors in there.

No shields and I've checked the caps. The supplies look stable and
do not have excessive ripple. It does "sing" a little bit, but from
the way the factory slobbered glue over all the ferrites and diodes,
I'd guess that was normal for this supply.

 

[Bill S]

Oops, make that 14,000 pF or .014 uF. I must have been thinking
about something else when I typed that.