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Model 8340A - Service
then something off the board is at fault.
Finally, look at LRSP, TPll, on the ASS sweep Generator board. If
it is stuck LOW, troubleshoot this problem.
If the three lines just discussed, LBX, HSP and LRSP are all
HIGH, then the problem is indeed on the sweep Generator board.
Reinstall the Marker/Bandcross board and consult the
troubleshooting section for the ASS sweep Generator board.
Incorrect sweep
If the instrument sweeps, as defined above, but the YO does not
sweep or the frequency limits are incorrect, check the two sweep
ramps from the ASS Sweep Generator board, 20-30 SWP (TP8) and
VSWP (TPlO). The sensitivities of these lines are discussed
below.
YO sweeps widths >S MHz are derived from VSWP. Note that the
instrument sweep width, delta F, is related to the YO sweep width
by the harmonic number of the band being used. For example, if
the instrument is sweeping from 8 to 10 GHz, the instrument sweep
width is 2 GHz. However, this is the second harmonic of the YO so
that the YO is sweeping from 4 to S GHz; a sweep width of 1 GHz.
The sensitivity of VSWP is +2 volts/GHz of YO sweep width. In the
example above, VSWP should be a ramp starting at zero and going
to +2 volts.
If VSWP is correct, then look at PRETUNE (TP3) on the AS4
.Pretune/Delay Compensation board. It has a sensitivity of -2.S
volts/GHz of YO frequency. In the foregoing example where the YO
swept from 4 to S GHz, PRETUNE should go from -10 to -12.S volts.
If PRETUNE is correct, look at SENSE (TP4) on the ASS YO Driver
board. This point has a sensitivity of about -2.34 volts/GHz of
YO frequency. If this is correct, the problem is most likely in
the A44 YIG Oscillator assembly.
YO sweep widths
<
S MHz are derived from 20-30 SWP. The
sensitivity of 20-30 SWP is related to YO sweep width but changes
depending upon the particular sweep width selected, as shown in
Table 80-1.
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