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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Zenith SS2712VK9 Horizontal "Breathing"
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. |
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How about posting the chassis series, or module number, year of
manufacture? |
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I tend to define “breathing” as a uniform, repetitional slow time constant of change, while what you describe is random in its occurrences.
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. But we still don’t know the manufacture age …listed on the back model tag…. or the sets module complement. 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. If its the first symptom, the overall hoz drive/sweep level is changing. If the latter you are experiencing a cutting in and out of the pincushion correction circuitry. 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 ( Venetian blind adjustment rod, etc…[let your wife figure that one out…-12 in shorter rod]) . This will provide a protective/insulated rod to tap upon suspected components with. The set is operational with the back off and a stable still picture from a cable bulletin board type of channel or the stable self produced logo from a DVD player is utilized. Observing the reflection on a frontally placed mirror , components in the hoz sweep and pincushion circuit are light/moderately tapped while the pattern is 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 the right rear area, working forward. 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. 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 , otherwise you will be safe by your using the isolation and distancing provided with the acrylic rod. If detected, a touchy part will justify an almost microscopic inspection of its solder connections for it being almost floating within its solder connection blob…thus necessitating a rosin fluxing and a reflow soldering with fresh solder. Standing by 73’s de Edd Last edited by Edd Whatley : June 2nd 05 at 11:52 AM Reason: typo |
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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. 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. |
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#8
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Oops, make that 14,000 pF or .014 uF. I must have been thinking
about something else when I typed that. In article , says... 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? |
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