Jl6 Operating Hints - Tektronix DAS9100 Service Notes

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w2 Issue 13-20
Jl6 OPERATING HINTS
REF: Jl6 Manual 070-1879-00
The following article provides some
helpful hints for use of the Jl6.
This infomation can help the
technician achieve more accurate and
repeatable results when adjusting the
color temperature on color picture
monitors.
J16
Photolleter Operating
Reca.endations
Many engineering and manufacturing
areas are using Tek Jl6 photometers
for measuring CRT luminance and
setting color balance of white fields.
I have observed several problems which
seem
to
reoccur. The following are
some reconnendations regarding the
correct or at least improved
techniques for making these
measurements:
-2-
October, 1883 laeue
31
1) Zerofng--This fs undoubtedly the
greatest single cause of errors with
the Jl6 and can occur with any of the
probes. Due to variations in silicon
input bias current, the zero should
always be rechecked when changing
probes and when the photo-diode
temperature changes. This fs most
noticeable on
r.t.
powered Jl6 1 s where
the photo-diode is positioned directly
over the
r.t,
power supply when plugged
into the top of the Jl6. Also when
using the
r.t,
power supply, continuous
operation or at least 1/2 to 1 hour
wamup is best to minimize zero drift
on the most sensitive ranges.
The Jl6 uses a mono-polar DVM circuit
which will still read 000 even when
the zero is offset in a negative
direction. This has the appearance of
non-linearity especially at low light
levels. Also the same reading will
not be obtained when changing to the
next range. To let the operator know
that it fs incorrectly zeroed, the
minus sign fs wired to indicate that
the zero fs offset in a negative
direction. To correctly zero the Jl6,
cover the sensor and adjust the zero
adjustment on the O.lX range until the
minus sign just flickers on and off.
An alternate
aethod
fs to adjust the
zero until a reading of typically 5 fn
the last place dfgft fs obtained.
This reading fs checked often when
using the most sensitive ranges. If
the Jl6 zeros correctly on the XO.l
range but fs incorrect on the XlOOO
range, ft fs an fndfcatfon that the
internal DVM zero needs readjustment
according
to
the procedure fn the
manual.
The zero procedure fs more complex
when using the J6523 1 luminance
probe--enough so that I reconnend use
of the Minolta 1 spot meter, ff
possible, rather than the Jl6/J6523.
The Minolta has auto ranging. no
zeroing required, compact size and a
display that fs visible through the
eyepiece used for sighting. The
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