HP 70908A, Service Manual

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If Y ou Have V erication T est F ailures
The following troubleshooting instructions are grouped according to module verication tests .
If the RF section fails a verication test, look up the test in the list and follow the instructions .
Before troubleshooting, always check to ensure that the failure is not caused by the test
equipment.
If T est 01. Flatness or T est 02. Low Frequency Flatness < 10 MHz F ails
If any atness calibration and verication routines fail, analyze the failure to determine the
location of the malfunction.
T o solve this problem:
1. If the failure occurs in band 1H0 (100 Hz to 2.9 GHz), anything between the RF input
connector and the A11 last converter can cause the problem. V erify that there is a 15 dBm
LO output signal going into the A15 RF 1st converter LO input jack at the failing center
frequency . If the LO signal is missing, troubleshoot the A1 leveling amplier . Also check
the A9 2nd converter PLL. (Refer to \Troubleshooting the A1 Leveling Amplier " and
\Troubleshooting and Alignment of the A5, A7, A8, A9".
2. If the failure is not frequency-dependent but exists across the entire band, check the
A4 input attenuator and IF paths for high conversion or insertion loss .
3. If the failure occurs in bands 1L0, 2L0, or 4L0 (2.7 to 22 GHz), verify that the LO input
signal from the multiplier to the A3 SYTFMD is 14 dBm (+12.5 dBm in 4L0 band). If it is
not, troubleshoot the A2 LO multiplier . (Refer to \Troubleshooting the A2 LO Multiplier ".)
Anything between the RF input connector and the A3 SYTFMD can cause a failure in these
bands .
4. If necessary , obtain service from Hewlett-P ackard. (Refer to \If Y ou W ant Hewlett-P ackard
to Service Y our RF Section " in Chapter 1.)
If T est 03. Attenuator A ccuracy F ails
If any attenuator accuracy routines fail, the failure must be analyzed to determine the location
of the malfunction.
T o solve this problem:
1. If the failure is greater than 8 dB, troubleshoot the A12 controller circuitry
(A12U8, U9, U20) .
2. If the failure is less than 8 dB or if the A12 controller is not at fault, troubleshoot the
A4 input attenuator .
3. If necessary , obtain service from Hewlett-P ackard. (Refer to \If Y ou W ant Hewlett-P ackard
to Service Y our RF Section " in Chapter 1.)
If T est 04. Front P anel LEDs F ails
If any front panel LED routines fail, the failure is most likely on the A12 controller .
T o solve this problem:
1. Check that A14 front panel board is receiving signals from the A12 controller (A12J7).
2. Check that transistors A12Q1 and Q2 have +0.7 V at the emitter when the LEDs are on.
3. If necessary , obtain service from Hewlett-P ackard. (Refer to \If Y ou W ant Hewlett-P ackard
to Service Y our RF Section " in Chapter 1.)
4-16 T roubleshooting