HP 8340A Service Manual page 70

M/N UNLOCK TROUBLESHOOTING
In order for the M/N section to lock up, the Reference Section
must be locked.
Block Diagram)
Check that a 20 MHz signal at 0 dBm +3dB is coming out of A29J2.
If there is no 20 MHz signal or it is low in power, then there is
most likely a problem on the A29 Reference Phase Detector board.
Check that there is 400 MHz at -10 dBm + 3dB coming out of A30Wl.
If there is no 400 MHz signal or it is Iow, then there is probably
a problem on the A30 VCXO board.
If both of the above signals are correct, then the problem is most
likely on the A31 M/N Phase Detector board or the A33 M/N Output
board.
Set up the 8340A by pressing
[GHz], [SHIFT]
13. The number 08 is the M DIVIDE number and number 13 is the N
DIVIDE riumber. In the first frequency wind6w is a frequency that
is expected out of A33J2 M/N OUT. Measure the frequency out of
A33J2. (NOTE:
have the 8340A and the measuring device, ie. counter or spectrum
analyzer, both'locked to the same 10 MHz standard.)
If the measured frequency and the frequency in the first window
are the same and the M/N Loop is still unlocked, then the problem
is most likely on the UNLOCK indicator portion of the A31 M/N
Phase Detector board or the UNLOCK Detector portion of the A59
Digital Interface board.
tf there is no signal out of A33J2, then the problem is most
likely on the A33 M/N Output board or the A32 M/N vco.
v, Adjustments, for details on verifying the M/N vco and Output
board.
If the measured frequency and the indicated frequency do not
match, then the problem is most likely on the A31 M/N Phase
Detector board or the A33 M/N Output board. It is now important to
see if the M/N output frequency is off due to divider failure on
A31 or vco tuning failure on A32 or A33.
Press
[SHIFT]
step the CW frequency in 10 MHz increments. For each 10 MHz step,
the "M" Divide number will change by a value of 1. Step the CW
frequency from 2.49 GHz to 2.3 GHz
each step, record the measured M/N output frequency and the
frequency displayed in the first window.
Check the list of frequencies. If some of the measurements match
8-92
Model 8340A - Service
(Refer to Figure 8B-2,
[INSTR PRESET]
In the "POWER dBm" window are the numbers 08
[Ml].
When measuring the M/N frequency, it is advisable to
[CF] [l) [O] [MHz]
Scans by HB9HCA and HB9FSX
Reference Loop-M/N Loop
[CW]
. This sets the 8340A up to
[CW)
("M" Number from 8 to 27). At
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See Section