Agilent Technologies 8590 Series Service Manual page 430

Analyzer Options and Block Diagrams
First LO Distribution Amplifier (LODA) 8593E, 8594E, 8594Q, 8595E, 8596E Option 009
IS THE FAILURE IN A SINGLE CHANNEL BANDWIDTH?
Comments
Failures can appear
in multiple places in
the EVM test across
multiple-channel
bandwidths and
symbol rates,
regardless of the
preamplifier settings.
430
TREE 4: EVM Problems
Problems/Reasons
The problem is in the main
demodulation path used by all EVM
test modes.
Diagnostic/Fix Action
1. Check the adjustment of the
71.025 MHz oscillator on the RF
option board. The nominal setting at
room temperature after warmup and
instrument preset (PRESET) of the
instrument should be 71.025 MHz.
If it has drifted off frequency, use
a tweaker to adjust C402 to bring
the frequency to 71.025 MHz.
Watch the signal. Is it stable, or
does it drift again?
If it drifts again, Q400 is
probably bad. Q400 is a specially
selected 2N3904 transistor. Check
with the division to obtain an
approved replacement.
Rerun the EVM test to check if the
problem is resolved. If not, proceed to
step 2
.
2. Replace the RF board with a
"known" good board. Does the
instrument now pass the EVM
test?
If so, save the bad board and the
matching test data for division
analysis.
step 3
If not, continue to
3. Replace the DEMOD option board
with a "known" good board. Does the
instrument now pass the EVM test?
If so, save the bad board and the
matching test data for division
analysis.
step 4
If not, continue to
4. Replace the DSP option board with
a "known" good board. Does the
instrument now pass the EVM test?
If so, save the bad board and the
matching test data for division
analysis.
If not, after swapping to a full set
of "known" good boards, set the
instrument aside for further
analysis.
.
.
Chapter 10