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77777 5555. FCOUNT is not toggling (U27 pins 9,
40). 1689-4702 Analog & Control board requires
service by trained personnel.
77777 3333. DMSR (U27 pin 8) is stuck low.
Integration failure. 1689-4702 Analog & Control
board requires service by trained personnel.
77777 2222. CMP-L (U64 pin 8) is stuck high .
Deintegration failure. 1689-4702 Analog & Control
board requires service by trained personnel.
77777 1111. DBIG (U27 pin 2) is stuck high.
Deintegration failure. 1689-4702 Analog & Control
board requires service by trained personnel.
66666 XXXX. Stuck key or detector scale factor and
zero bias test failure; the Digibridge will loop, auto-
matically repeating the test and updating the display.
XXXXX is the magnitude of "zero" measurement,
normalized to 1.
COMMENT: The "zero" measurement includes a se-
quence of five dual-slope conversions (measurements
of voltage coming into the detector from the instru-
mentation amplifier) . Frequency is 1 kHz; test signal
level is 75 mV. The signal component is removed by
averaging the results of two dual-slope conversions,
sampled in opposite phases. The detector is supposed
to be biased so that its "zero" output is essentially in
the center of its operating range. For convenience, the
CPU divides the "zero" measurement by its normal
value and displays the result. Consequently, the ideal
value for XXXXX is 1.000. If it is less than 0.875 or
more than 1.125, the test fails.
Verify that all keys on the keypad are working. If no
fault in the keypad is found, 1689-4702 Analog &
Control board requires service by trained personnel.
ANALYSIS PROCEDURE: Check the following
circuits:
Service and Maintenance
555 D XXXX. Signal strength check failure; the
Digibridge will loop, automatically repeating the
test and updating the display. The digit D indicates
the range and voltage level used. (See below.) Test
frequency is 1 kHz.
COMMENT: Possible cause is having EXTERNAL
BIAS switch ON during power-up. The effect depends
on what is connected to the EXTERNAL BIAS con-
nector and what is in the test fixture. This switch must
be OFF to assure normal power-up routines. Check
to make sure that the charged capacitor protective
fuse F1 has not blown, the effect is similar (see sec-
tion 5.7.3). Remove all DUT from Digibridge during
power up. The ideal value for XXXX is about 0.64. If
it is less than 0.250 or more than 1.000, this test fails
ANALYSIS PROCEDURE: See below; depends on the
failure display, which is coded to indicate test voltage
(high or low) and range of the failed test.
5555 5 0000. (Confirming symptoms: If you press
START repeatedly until the instrument completes its
self check, the BIAS ON indicator will be lit even
though the EXTERNAL BIAS switch is OFF, no bias
is applied, and INT BIAS has not been selected.) The
fault is probably in the 6-wire connection between
keyboard and main board. Check to be sure that the
cable connector properly engages all 6 pins at the
keyboard.
555 5 XXXX. Low voltage (75 mVrms), range 4.
1689-4702 Analog & Control board requires service
by trained personnel.
5554 XXXX. High voltage (1.275 V), range 4.
555 3 XXXX. High voltage (1.275 V), range 3.
555 2 XXXX. High voltage (1.275 V), range 2.
555 1 XXXX. High voltage (1.275 V), range 1.
1693 RLC Digibridge
125
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