Good deal! Precisely what I was hoping to to see.
First, let me say that I've seen much worse geometry situations than what you've posted. And from what I've seen here, that slight upward bow is quite common on the Sony HD tubes. That's the "good" news. Now for the not so good news...
All I can really tell you is how I'd approach the issue on my 34XBR800 TV, which may not be correct for your TV because it has the add'l zoom/stretch features for HD signals. That's why I suggest poking around a bit to see if you can find some more info on the geo controls for your specific model.
The upward bow on the bottom and "downward bow" on the upper corners are really the same issue. You've got an upward bow distortion that's effecting the entire raster.
Fixing that can be a bit tricky because there's only one control for vertical bowing (2170D-1/VCEN) and it's a "global" adjustment (on my TV anyway)... meaning it only stores one value, and applies it to all resolutions and zoom/stretch modes on the TV. So you cannot tweak the vertical bow differently for 480i than you do for 1080i, for example. One VCEN value has to work for all resolutions and zoom/stretch modes on the TV.
If the distortion is pretty consistent across all of the zoom/stretch modes for both SD and HD signals, then it's a little more manageable. But you should be aware that changing VCEN for one resolution and zoom mode will effect the geometry on the other resolutions and zoom/stretch settings on the TV.
Before you attempt to make any tweaks, I'd recommend that you look at a grid pattern like the one above in all of the zoom/stretch modes on your TV using both an SD (480i or 480p) and HD (1080i) video input, to see if they all exhibit the same upward bow distortion... unless
you don't care how the picture looks on the SD sources.
(I only use 1080i on my 34XBR800, so I didn't even both worrying about or fixing the distortions on SD zoom/stretch modes.)
Anyway, that's the first issue you have to contend with. The other issue is that VCEN will tend to shift the raster upwards or downwards a bit. So you may be able to fix the bow distortion, but your image could be shifted off center toward the top or bottom of the screen as a result. To correct that you'll need to use some of the vertical position controls. And the amount of shift may be slightly different for SD, HD, and different stretch/zoom modes. So you may need to make small tweaks to re-center the raster for all the different SD and HD zoom/stretch modes.
There are a couple different controls for vertical position. (Edit: See note in Post #14
below about vertical controls in the User
menus that I forgot about when originally composing this post.) The most obvious one (in the Service
menus) is 2170D-1/VPOS. This is also a global control though, which only stores one setting for all modes and signals on the TV. And you may also find that it "interacts" with the VCEN control in such a way that it tends to undo the corrective tweaks made to VCEN.
There is another vertical position control in the SM that you can probably use to get around this problem: 2170D-1/SCRL. On my TV, SCRL is sensitive to both resolution and zoom/stretch modes. IOW, it stores different values depending on the zoom/stretch mode the TV is set to, and whether the input is SD or HD. So this can potentially be used to re-center the raster for other signals and zoom/stretch settings. My suggestion is to leave VPOS at or near the original setting on your TV, or around 31. And consider using SCRL to tweak the vertical position of the raster (if the vertical controls in the regular User menus don't suffice).
There are other vertical position controls in the MID group settings as well, but I recommend staying away from those, because they have even more complex interactions than the ones discussed above. Whatever you do, DO NOT
change any of the sizing
controls in the MID groups, because you can potentially loose lines of resolution in your images if you do that. The MID settings are digital controls, while the geo controls in the 2170D-1 section are all analog, so there is less potential harm that can be done with the latter. If you do not have a precise idea what a control does, it's best to leave it alone and not touch it, or you could screw things up on your TV.
VCEN and 2170D-1/VPIN are also inter-related. VPIN is the vertical pin cushion control. The basic strategy is to adjust VCEN so that the bow distortion is symmetrical, and there's either a slightly outward bow on both the top and bottom edges of the raster, or a slightly inward bow on both.
Imagine that the lenses in this illustration
are the video raster on your TV. The top lens is "double-convex", and the equivalent of a symmetrical outward bow. The bottom lens is "double-concave" or similar to symmetrical inward distortion. Obviously the distortions would be much more
subtle on your TV. But if you can get the distortion symmetrical with VCEN, then you can fix any remaining pincushion effect left in the image using VPIN. (VPIN is also a global control on my TV, so there's only one setting for all zoom/stretch modes and resolutions.)
A ruler is your friend. Don't trust your eyes. The patterns that I supplied in the Sony SM thread are ruler accurate, so if you measure from the bezel of your TV to the edge of the grid at different points along the bottom or top edge of the screen, the distance should be approximately the same.