6-40
4. Replace A11U670.
3. Check for a square-wave signal at A11U680 pin 2. If present, replace A11U680.
2. Check for a 3 V square wave at A11U680 pin 18. If present, the problem is a defective cable con-
nection from A11 to A13 boards.
d. Check emitter of
0831
is the same as the base of
0831.
c. Check U831 pin 1 for +5.1 V.
b. Check U831 pin 2 for +2.4 V.
a. Check U831 pin 8 for a signal.
1. Check for a 3 V square-wave signal at the forward end of R831 (100 n resistor under A13U831
near the cable connector). If present, the problem is in U831, U731,
0831,
or one of the parts in
that output amplifier circuit.
The calibrator circuit can be split into two parts. The source of the signal (CALCLK input at W122 pin
2) and the analog output stage on circuit board A13.
Make sure that you have not made the mistake of viewing the Calibrator signal output with
a 10
Mf)
probe and have the channel in 50
f)
input termination.
NOTE
Calibrator (schematic diagram 13):CALIBRATOR
PROBLEMS
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.
1. Connect a probe to the emitter of A120592. Then select the B TRIGGER SOURCE menu and
press the BEZEL switch for WORD. 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).
Remove the word trigger probe, then:
Bell Circuit (schematic diagram 20):
BELL
PROBLEM
12. The two remaining analog levels are the CH 1 and CH 2 50 ohm overloads. Check that they are
approximately 3 Veach.
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).
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.
9. Connect the test scope to observe the AOUT2 signal at R809. This signal is from the Auxiliary
Front Panel circuitry.
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).
Table 6-6 (cont)
Maintenance-2430 Service
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