Old Panasonic CRT TV, Adjusting Picture Geometry

"AR"

If the pic size also changes with brightness, that indicates poor regulation of the EHT.

EHT setting is normally via a trim pot on the main PCB.

.... Phil

Pictures don't just get bigger. The only way for that to happen is as Phil said, something happens to the HV, but that only applies to sets with separ ate HV and horiz. sweep. Your set DOES not have it I can be almost 100% sur e. Panasonic simply did not do that any more. Maybe in a Sony or Mits. So n o fingerpoken ! (or it's digital equivalent) Plus, Panasonic sevice menus a re unfriendly and unforgiving.

What is very likely is that you are watching it through a set top or cable box. Most of the modern cable boxes at least have aspect settings to accomo date newer sets with 16:9 aspect ratios. This is where the problem usually is. With a set top or dable box, go all the wasy thorugh the menus to find things like "aspect", "zoom" and the like.

In case you are not using a set top or cable box, or even if you are, go th rough the user menu on the TV as well to find similar settings because quit e a few of the more modern 4:3 sets also have then, to fill the screen on 1

For it to require adjustment in the service menu, two parameters in EPROM w ould have to increase. Two out of maybe 100.

Ain't happenin.

I have trouble imagining a set with separate horizontal sweep and HV -- especially a set with a reasonably sized CRT.

The "flyback" HV circuitry can certainly lose its regulation, while the sweep continues to work correctly.

CRT VGA monitors.

I said set, not monitor. And I assume you're referring to auto-sync monitors. In a flyback HV system, you'd have trouble maintaining a constant HV as the sweep frequency changed.

I have trouble imagining a set with separate horizontal sweep and HV -- especially a set with a reasonably sized CRT."

One comes to mind, the Sony KX 2501. It was dubbed Profeel. It had separate HV and sweep. It was a bit strange oin a way, under secrtain conditons wwh en the scene got brighter the raster shrunk slightly because of the mass of the electron beam. That is why three tube CRT based projectors have these seemingly useless couple hundred Kohm resistors or whatever in series with EACH CRT anode lead inside the HV splitter. This compensated the deflection sensitivity, if not, the convergence woulg tet thrown off with changes in scene brightness.

Quite a few monitor quality sets used disctrete HV. Proton, Sony, Mits., Pi oneer. The fad didn't last long because back then component count mattered. now it does not as much.

The practice did continue with Sony in direct views into the XBR400 series at least, and then others did also. Ironically, Sony abandoned it.

In the latest CRT based RPTVs, they use an algorythm in the jungle IC to mo dify the geometry to compensate for both the variation of voltage and curre nt in the HV, or ultor voltage. They stopped regulating it. You saw nothing .

I remember when a weak 3A3 would give you a zoom effect from the brightness control. That HV load made a loss across the HV rectifier only, and did no t affect the sweep.

That is why they used seperate circuits for HV and H sweep. Some of those monitors could also display NTSC, and were used as TV sets. I have a dying Samsyng LCD monitor here with a place to install a ATSC TV tuner, so the concept didn't go away with flat panel displays.

and sweep. It was a bit strange oin a way, under secrtain conditons wwhen the scene got brighter the raster shrunk slightly because of the mass of the electron beam. That is why three tube CRT based projectors have these seemingly useless couple hundred Kohm resistors or whatever in series with EACH CRT anode lead inside the HV splitter. This compensated the deflection sensitivity, if not, the convergence woulg tet thrown off with changes in scene brightness.

Pioneer. The fad didn't last long because back then component count mattered. now it does not as much.

least, and then others did also. Ironically, Sony abandoned it.

modify the geometry to compensate for both the variation of voltage and current in the HV, or ultor voltage. They stopped regulating it. You saw nothing.

control. That HV load made a loss across the HV rectifier only, and did not affect the sweep.

Do you remember the Zenith color TV with "built in zoom"? I think that was the same chassis had their silly 'Phonevision' to answer the phone through your TV.

The old Zenith with zoom, oh yeah. However those didn't really vary the HV, at least not on purpose. The modified the H pulse to the yoke and cranked the V height.

When you get to the HD TV sets, you will find some with separate HV because alot of them didn't actualy upconvert. You had 1080i and 480p, a 480i sign al really just went through a line doubler. RCAs dealt with the differences in sweep using the flyback, in fact in the DTV3XX series they varied the B

• voltage to compensate. That's why there aren't too many of them around an ymore, it was not a good idea. The ITC and ATC chassis were quite a bit mor e reliable.

The HD Sonys have a separate flyback driven from a totem pole of two MOSFET s. The frequency is does not give a shit Hz, but it is higher than the swee p, which seems like a good idea.

Separate HV was really popular in CRT based RPTVs. In those, it solved alot of problems all at once.

I can't think of any Panasonic direct views with separate HV, and now that I mention it, neither in their RPTVs. There could be a model or two out the re I have not seen though.