HP 3455A Operating And Service Manual page 130

SERVICE GROUP A
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8-A-1. TURN-ON CIRCUITRY (INGUARD AND OUTGUARD).
8-A-3. Inguard/Outguard Isolation.
8-A-4. Assuming that the power supplies of the 3455A are good, the Instrument Half Splitting
Technique (paragraph 8-176) should be the first step in isolating turn-on failures. Either the inguard
or the outguard section could hang up the 3455A's turn-on sequence. The front panel indication does
not tell where the fault is located. Therefore, the Half-Splitting Technique should be used to isolate
the fault between
inguard or outguard section of the 3455A. If an extra 3455A
and an In-
guard/Outguard Service Cable is not available, the method described in Figure 8-45 may be used.
When it is determined which section of the 3455A is at fault, go to the appropriate troubleshooting
section in this service group (see paragraph 8-198 and Table 8-3).
8-A-5. Outguard Troubleshooting (Schematic 8).
b. Add A1C46 (part number 0160-3622) if the 3455A does not have one (schematic 8).
c. Troubleshoot the outguard turn-on circuit (A1U5, U26, and associated components). Check for
a pulse at turn-on, as shown below, which can be seen at U26 pin 9. This pulse connects to inverter
&
s5V
J ——— '50-250msec ——>}
d. Check the Nanoprocessor interrupt circuit for correct operation. The IN ENA line should be
held high and the IN REQ line should either toggle from high to low to high, or remain high. If these
conditions do not exist, then troubleshoot the interrupt circuit (A1U46, U47, U53, and U55). The
turn-on circuit (A1U26) must be working before troubleshooting the interrupt circuit.
e. Using the Signature Analysis routines in Figure 8-H-20 to 8-H-27, troubleshoot the outguard
logic. If any difficulty is observed using the signature analysis routines, go to Service Group F,
paragraph 8-F-1 for troubleshooting hints.
f. Using the information in Service Group F paragraph 8-F-1, troubleshoot the outguard logic.
8-A-6. Inguard Troubleshooting (Schmatic 5, 6, 7).
8-A-7, The Inguard Mother Board (A10) and or the A/D Convertor Board (A14) may cause turn-on
failures. To isolate one from another swap a good A/D
convertor board (A14) with the one in the in-
8-A-8. A10 Motherboard Troubleshooting (Schematic 5, 6, 7).
8-A-9. Use the following steps in the order they are presented to troubleshoot the Inguard Mother-
board (A10).
8-40