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Tom Herman's Step by Step Focus Adjustment
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Focusing the TP61H95 (Tom Herman 10/23/99)
"While removing the screen protector yesterday (a 200% improvement
!!), I decided "hey, why not fine tune focus the set as well?"
Ideally the focus procedure I’m going to describe should be done
first – it’s more efficient this way– but it doesn’t have to be done
first.
The Service Manual is very useful to have on hand, as a general
reference. Be warned, it’s not always clearly translated, and in one regard
(described later) I think it’s just plain wrong.
Other useful materials to have on hand:
- Diapers, previously washed to soften them.
- Can of compressed air.
- Bright flashlight
- Distilled water; Windex
- Optional: Kodak brand Lens cleaning fluid & Kodak Lens tissue
Let’s begin.
Remove the speaker grille, the lower plastic cover, and finally the screen & bezel
assembly.
Click to enlarge
Do a general inspection of the mirror for cleanliness. Shine a bright
flashlight obliquely on the mirror to accentuate any smudges or debris. Mine had a big
greasy fingerprint on it!
Note, Bob Jones posted a very detailed post a few months ago on
complete optics cleaning. My set is still pretty clean (but wasn’t perfect), so I
didn’t think I needed to do the full procedure.
The mirror appears to be "front silvered" , be very gentle so
as not to scratch the front reflective coating. Only if necessary, use a soft cloth (e.g.
a previously washed diaper) dampened with distilled water to clean any smudges off the
mirror.
I had to use a diaper very lightly dampened with Windex to clean the
fingerprint, but I immediately re-wiped the area with distilled water. Otherwise the
ammonia in the Windex could harm the coating.
Remove the lens from each CRT & rotate it 180 degrees, so that the
wingnut faces toward the back. I used a technique that allowed me to focus the set from
the front, so I didn’t strictly need to do this, but it will make the lenses
accessible from behind the set should it ever be necessary.
Even if you don’t choose to reverse the lens, I recommend taking
it off anyway to inspect for debris (use the flashlight).
Dislodge any gross debris with the compressed air, both from the lens
& the face of the CRT (actually a depressed acrylic cover, liquid coolant is between
this cover & the CRT.
Gently clean both ends of the lens & face of the CRT cover with the
Kodak fluid & tissue. If you don’t have any, use a soft diaper BARELY moistened
with distilled water.
The technique for cleaning a lens is to moisten a "poofed up"
or wadded up piece of lens tissue with a drop of fluid.
Start at the center of the lens & wipe slowly outward, in a spiral,
to the lens edge. Take a dry tissue & wipe gently from center to edge, in a spiral, to
dry it.
If any lint remains, use the compressed air to blow it off. Inspect
with flashlight. Repeat if needed.
Power on the set. Let it warm up for at least 30 minutes on a TV
channel (don’t put a static test image on). While waiting, go remove the screen
protector. Following a suggestion from Aaron Madrid, I put the protector BEHIND the
Fresnel & Lenticular screens , rather than eliminate it from the 3 screen
"sandwich". Leave the screen off the set for now.
Getting back to the set, enter Service Mode and press ‘7’ to
enter the Convergence Grid. Since the screen isn’t on the set, be familiar with how
to do this, as you won’t have the usual visual cues to look at.
Electronic focus – "Focus VR" – focuses the
electron beam spot on the CRT. Mechanical focus – the lens assembly – focuses
the image on the screen.
Page 6 of the Toshiba service manual says to do mechanical focus first,
then electronic Focus VR. THIS IS JUST PLAIN WRONG!
From basic optics theory , this didn’t sound right. I played with
it to convince myself. If electronic focus is wrong, no amount of mechanical lens focus
will ever make it correct. Similarly if mechanical focus is wrong, no amount of electronic
focus will make it right. The electronic focus HAS to be done before the mechanical focus.
The 3 "Focus VR" knobs control electronic focus of the CRT.
This is the LOWER set of 3 knobs that was concealed behind the plastic cover. From left to
right, the knobs are Red, Green, Blue (same as CRTs).
Turn on only the Red CRT (green & blue ‘off’). Look at
the Red Grid image in the Lens from a distance of 6-12 inches. Slowly adjust the Focus VR
knob for the sharpest possible image.
A helpful technique is to ever so slightly, rotate the Focus VR knob to
either side of the optimal focus position. The human eye seems to more clearly detect
perfect focus, as you "rock" back and forth out of perfect focus. Those of you
who have manually focussed a camera, may be familiar with this technique.
Turn on the Green CRT only, and repeat Focus VR on the Green.
Turn on the Blue CRT, and repeat Focus VR on the Blue. The Blue CRT is
aggravating, and will never look as good as Red & Green. Something about the blue
phosphor or design of the CRT makes it impossible to get the same crisp focus.
I noted that the overall light output of each CRT, apparently drops to
a MINIMUM at the point of sharpest focus. This effect cannot be easily exploited with the
unaided eye alone. But it does suggest that using a light meter, and adjusting Focus VR
for lowest light output, may be a way to objectively & repeatably set for sharpest
focus, especially the Blue (which can drive you batty).
Now that we have sharpest image possible on the face of the CRT,
we’re ready to do mechanical lens focus. Mechanical focus will produce the sharpest
image on the surface of the screen. This is done by loosening the wingnut on the lens
assembly, and pushing on the wingnut to rotate the internals of the lens.
The problem, of course, is how to focus on the screen, since you need
to have the screen removed to access the lens! Some repeatedly install & remove the
screen. But since you need to gently "rock" the lens back & forth to find
the sharpest focus, I don’t see how this can work properly. Others will access the
lens from behind, and use a mirror or helper. I didn’t have either. Besides, I
didn’t think by looking at a distant image in a mirror , that I could see it well
enough to do a critical focus. And it wouldn’t work at all for those of you who have
the set mounted in a wall or custom cabinetry.
This is what I did :
The front edge of the TP61’s cabinet is "rabbetted" to a depth of
precisely 1 inch. The screen bezel bottoms against this rabbet.
Click to enlarge
The next photo is not clear, but the distance from the back surface of
the bezel, to the Fresnel screen layer, is almost exactly 2 inches. What this is saying ,
is the imaging plane is exactly 2 inches out from the edge of the rabbet.
Click to enlarge
This is what I did :
The front edge of the TP61’s cabinet is "rabbetted" to a
depth of precisely 1 inch. The screen bezel bottoms against this rabbet.
On my power miter saw, I cut out some blocks from 1x3 wood stock that
are exactly 2 inches long. I clamped the block to the TV’s cabinet, butting up to the
edge of the rabbet. I clamped one block at the left & another block on the right, near
the horizontal cenetrline. The front of the blocks is now exactly at the image plane.
Click to enlarge
I taped together a long length of semi-transparent tracing paper, and
taped it tightly across the two blocks I clamped to the set. The tracing paper is at
exactly the same plane as the screen will be. The image of the Convergence Grid is now
clearly displayed on the tracing paper.
Turn on the Red CRT only, and adjust the lens assembly for sharpest
focus on the tracing paper. Tighten the wingnut on the lens, making sure the focus
doesn’t change as you tighten.
Repeat for the Green & Blue. The Blue will not focus as sharp,
limited by the best electronic focus previously achievable.
Click to enlarge |
Click to enlarge |
At this point, one would be ready for the
mechanical & geometry alignment.
If you choose not to do that right now, the set will still require
Service Convergence. Reinstall the screen by reversing the disassembly steps. Do the
full 60 point Service Convergence.
It’s been noted elsewhere, that re-adjustment of the focus could
subtly shift the gray scale & color balance. Since sharpest focus results in lowest
CRT light output, you can see why gray scale might shift.
To my eye, any gray scale change on my set was not readily apparent –
but the untrained, unaided eye is notoriously unreliable. Since my set was never ISF
calibrated, I doubt my set was ever 6500K accurate to begin with.
With possible exception of gray scale, I’m pretty happy with the
TP61. The screen protector’s been removed, electronic & mechanical focus has been
done, and geometry & convergence are pretty darned good. The only thing task
remaining, is to get a good instrument assisted gray scale calibration & tracking
done."
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