MCi JH-400B Series Technical Manual page 20

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6.3
LIGHT METER SERVICING
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The LIGHT METER is basically a DIGITAL instrument, and must be
thoroughly understood before any servicing is attem9ted. a detailed
explanation is given on pages 3-9 and 3-10 of this manual.
Adjustments and calibration procedure is as follows:
1.
With all light meters and the Haster Board plugged in, verify
that the logic supply is Sv +0.2v on the Mother Board.
2. Check the + 15v supply to the !-1other Board.
3. Depress the HOLD but ton on the Has ter Board and measure the
voltage on the RA~1P bus. Adjust the OFFSET pot, Rl6, for
-0 .1
v.
(Channel Boards adjacent to the Master Board
may
have
to
be
removed
to
get at the OFFSET p::;t.)
Set the OSCILLATOR output for +4 dBv at 1 kHz. Assign to "TRKS".
Set console to
"MII\E"
mode.
4. Adjust the oscillator level for +4 dBv output level at the
channel line output of the channel being calibrated.
5.
Connect an oscilloscope to pin 6 of IC2 on the Channel Board
being calibrated. This is the output of a full wave precision
rectifier. Adjust R6 for a symmetrical waveforem.
6. Place the Channel Board in VU mode. Adjust the level pot, Rl,
for "0" VU display on the light meter.
("0''
vu
is indicated when
"0" VU level lamp just lights up).
7.
Repeat steps 4,5,& 6 for each Channel Board.
8 .
9.
After all the channels have been calibrated, key the
ON and OFF with the "TRKS" switch. Observe the rise
time on the display. They should all be identical.
ARE DIFFERENT, REPEAT STEP 5.
oscillator
and fall
IF THEY
[ : 1
Page
Switch the channel cards from VU mode to PEN< mode and again
key the oscillator Oi-J and OFF with the "TRKS" switch. Observe
that all meters display the level instantly and decay in two
seconds when the oscillator is turned OFF.
6-2 JH-400B