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Maintenance— 2440 Service
Table 6-6 (cont)
8.
Check that both sides of the pot have equal output range (approximately 0 V to 5 V) and that the
voltage level for each side of each pot moves smoothly from one extreme to the other as the pot
is rotated through the continuous range (not its end-switching region).
9.
Connect the test scope to observe the AOUT2 signal at R809. This signal is from the Auxiliary
Front Panel circuitry.
10. Momentarily short the shell of each of BNC input connectors to its coded-probe-switching ring and
observe that the voltage level for that connector goes from 5 V to 0 V.
11. Rotate the infinite rotate INTENSITY pot and check for smooth voltage level changes on both
sides of the pot (from approximately 0 V to 5 V).
12. The two remaining analog levels are the CH 1 and CH 2 50 ohm overloads. Check that they are
approximately 3 V each.
BELL
Bell Circuit (schematic diagram 20):
PROBLEM
Remove the word trigger probe, then:
1.
Connect a probe to the emitter of A12Q592. Then select the B TRIGGER SOURCE menu and
press the BEZEL switch for W ORD. The voltage should go close to + 4 V with about a 1 V p-p,
2 kHz square wave superimposed upon it (peak of 5 V).
If the 4 Vdc is not present, check the signal path back to A12U760 pin 16. If the 2 kHz is missing,
check back to the oscillator circuit A12U274.
CALIBRATOR
Calibrator (schematic diagram 13):
PROBLEMS
N O TE
M ake sure that you have not m ade the m istake o f viewing the Calibrator signal output with
a 10 MS2 probe and have the channel in 5 0 S2 input termination.
The calibrator circuit can be split into two parts. The source of the signal (CALCLK input at W 122 pin
2) and the analog output stage on circuit board A13.
1.
Check for a 3 V square-wave signal at the forward end of R831 (100
Q
resistor under A13U831
near the cable connector). If present, the problem is in U 831, U 731, Q 831, or one of the parts in
that output amplifier circuit.
a. Check U831 pin 8 for a signal.
b. Check U831 pin 2 for + 2 .4 V.
c. Check U831 pin 1 for + 5 .1 V.
d. Check emitter of Q831 is the same as the base of Q 831.
2.
Check for a 3 V square wave at A11U680 pin 18. If present, the problem is a defective cable con
nection from A 1 1 to A13 boards.
3.
Check for a square-wave signal at A11U680 pin 2. If present, replace A11U680.
4.
Replace A llU 6 7 0 .
6 -4 2
Содержание 2440
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