HP 70908A, Service Manual

Page: 80 / 335

If Y ou Have V erication T est F ailures
If T est 14. Miscellaneous Residual Responses F ails
This verication test checks for specic known residuals .
If any miscellaneous residual responses routines fail, the failure must be analyzed to determine
the location of the malfunction.
T o solve this problem:
1. Remove the A4 input attenuator ribbon cable from the A12 controller . If the residual
disappears , replace the A4 input attenuator .
2. F or N x 300 MHz residuals , verify that the \D" shaped chromerics and the RFI gasket,
located in the grooves of the A9 2nd converter PLL cover , have no discontinuities . Ensure
that the polyiron gasket is installed in the A11 last converter casting.
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 15. 321.4 MHz IF Out Frequency Response F ails
The usual cause of test failure in 1H0 band is 2nd-converter bandpass-lter alignment. F ailures
in the 1L0 band may be caused by YTF tracking of the A3 SYTFMD .
If any 321.4 MHz output frequency response routines fail, the failure must be analyzed to
determine the location of the malfunction.
T o solve this problem:
1. If 1H0 band fails , perform A djustment 22. 2nd Converter Bandpass Filter Tune .
2. If 1L0 band fails , perform A djustment 06. SYTFMD Oset Coil and A djustment 09. SYTFMD
Main Coil Alignment.
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 16. 21.4 MHz IF Frequency Response F ails
This test checks the overall lter response of the RF section IF output. At 300 MHz in 1H0
band and at 6.0 GHz in 1L0 band, the test veries correct alignment of the A3 SYTFMD ,
A9 2nd converter PLL, and A11 last converter .
The response is normally a function of the 321.4 MHz bandpass lter on the A11 last converter.
However , if any lters before the A11 last converter are not correct, this test can fail.
If any 21.4 MHz output frequency response routines fail, analyze the failure to determine the
location of the malfunction.
T o solve this problem:
1. Check that the RFI gaskets are not missing from covers or underneath printed circuit boards .
2. Check the output response of the 321.4 MHz at the rear panel jack.
3. If the response falls within the test limits of the 21.4 MHz output port, troubleshoot the
A11 last converter .
4. If the response does not fall within the test limits of the 21.4 MHz output port, check the IF
path until the faulty assembly is found.
5. 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.)
T roubleshooting 4-19