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KRX-593/793
ADJUSTMENT
SERVICE POINT
1. Timer accuracy improvement method:
(DISPLAY UNIT)
Q701
uPD75208CW-AS7
momo
r rn
ee
(Connected to the 12 V tine of
| the unit)
+B312V —=
High-impedance FET probe
"Unless available, make it for yourself.
Frequency counter
The timer accuracy is within +40 seconds for one month
as a standard. For improved timer accuracy, perform the
following procedure:
(1)
If the timer accuracy is without the standard, replace Z702
(L77-1176-05)
near the microprocessor IC on a printed
board.
(2)
Even if within the standard, for further improved accura-
cy, change the constant of C704 in the crystal oscillation
circuit of microprocessor Q701 and add a trimmer.
Adjustment method (Use a high-impedance buffer to avoid
frequency deviation.)
Connect a high-accuracy frequency counter to pin 30 by
way of the FET probe shown
above,
and adjust the
frequency fully up to the first digit of the Z702 reference
frequency 4,194,304 Hz. (Connect the negative (—) side
of the frequency counter to the GND side of C704.)
Notes: 1. As regards the positive (+) side of the frequency
counter, arrange as short a distance as possi-
ble between pin 30 of Q701 and 1P of the in-
put stage of the FET probe.
C704 constant
modification
Capacitance value of
additional trimmer
22 pF titanium
capacitor
(CC45 FCH1H220J)
20 pF (red)
CO05-0303-05
Q1: 2SK241(GR,
BL)
1: Drain (D)
6
5
a
2: Source (S)
3: Gate (G)
| |
(View from leg side)
Front panel side
C705
27P
Additional trimmer
'
|
i}
4
=
a
g
Ss
:
' i \ ' \
i]
4
1
¢704
Note: Disconnect the C704 connected on the
PC board,
and add a trimmer.
(It is
necessary to make a hole.)
Input: 1 MO
Next, connect a 22 pF titanium capaci-
tor on the rear.
2. Perform the trimmer adjustment after energiza-
tion of around
10 minutes
at normal
tem-
perature.
(3)
Monthly error calculation method
For example, when the result of measurement at pin 30
by the frequency counter is fx=4,194,275
Hz...
fx — fo
5
x the number of seconds
Monthly error [sec] =
taken for one month
4,194,275-4,194,304
4,194,304
x (60 x 60 x 24 x 30)
~ 17.9 [sec]
* A minus value as the monthly error
means a loss.
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