Agilent Technologies 8564EC, Service Manual

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Chapter 8 383
ADC/Interface Section
Keyboard/RPG Problems
4. Monitor A3U607 pin 8 with a logic probe. A TTL high should be
present when any key is held down. Monitor this point while
pressing each key in succession.
5. Check that the LKSCN lines (outputs of A3J602 pins 1 through 6)
read a TTL low with no key pressed. (Any TTL high indicates a
faulty A3 Interface assembly.)
6. Check that a pulse is present at each LKSCN output of U602 when a
key is pressed.
7. Check that only one input to U607 (LKSNS lines) goes low when a
key is pressed.
8. Check that U602 pin 9 (LKBD_RESET) pulses low when a key is
pressed.
9. If LKBD_RESET is incorrect and a pulse is not present at each of
the LKSCN outputs of U602 when a key is pressed, check for
LWRCLK and LSCAN_KBD.
RPG Interface
Refer to function block J of A3 Interface Assembly Schematic Diagram
(sheet 3 of 6) in the 8560 E-Series Spectrum Analyzer Component Level
Information.
U608B latches the RPG direction from the two RPG outputs,
RPG_COUNT and RPG_COUNT1. Counterclockwise RPG rotation
produces low-going pulses which result in a high output on U608B.
Clockwise RPG rotation results in a low output from U608B. U612A
provides the edge to trigger one-shot U423B, which generates a 90 ms
pulse. This pulse gates U610A for counting of RPG pulses by U606.
Gates U610D and U614D prevent retriggering of U423B until its 90 ms
pulse has timed out.
NOTE
Elsewhere, RPG_COUNT1 is referred to as RPG_01 and RPG_COUNT
is referred to as RPG_02.
1. Monitor A3U401 pin 2 with a logic probe or oscilloscope. Pulses
should be present as the RPG is rotated.
2. Monitor A3U608 pin 12 as the RPG is rotated. Pulses should be
present.
3. If pulses are missing at both points, check for power and ground
signals to A1A1W1 and A1A2W1. If both power and ground are
there, the A1A2 RPG is probably defective.
4. If pulses are missing at only one point, check for an open or short on
A1A1W1 and A1A2W1. If these cables are working properly, A1A2
RPG is probably defective.