HP 3562A, Service Manual

Page: 495 / 570

MOD E L 3S62A
S E RV I C E
3 . Phase Val ue Fail u res
The phase value is read from the phase latchs (A4 U23, U27). If the phase val ue fai l s,
the output value is probably fai ling too. (However, if the fai l u re message is 'LO I nt
C lock Phase Values FAI LS', 'LO Ext C lock Phase Values FAI LS' and the other LO
self-tests pass, the possible cause of the fai lure is the phase latchs A4 U23 and U27,
or A4 U47, US2, U32, U36 in the system bus i nterface.) If the phase value fai ls, use
signatu re analysis patterns LO DSA PA TT 1 and LO DSA PA TT 2 (in part B) as fol lows
to isolate the "fa i l u re:
LO DSA PATT 1
a. Start by checking the phase accu m u lator outputs (A4 US).
b. I f the phase accum u lator output signatu res are correct, check A4 U22 and U26.
c. Check A4 U68, US6, and US8 i n the control and timing circu its. Then check A4
U1 9, U31 , and U36 pins 2, 3, 4, 1 0 through 1 9 in the system bus i nterface.
d . I f any of the signatu res i n step c are wrong, check the i nput s ignals to the
components. If the inputs to the components are correct, the fail u re is most l ikely
caused by the phase accumu l ator.
LO DSA PATT 2
The phase accu m u l ator feeds its output back to the input. LO DSA PATT 2 breaks
this feed back loop. Start by checking the signatu res of A4 U1 1 and U1 6. Check the
signatu res of the other components i n the phase accu m u lator by moving forward and
back from A4 U11 and U1 6.
4. Output Value Fai l u res
The output value i n the exclusive OR of the S I N E and COS outputs which are shifted
into the LO output buffers (A4 U41 , U42). If the fail u re message is 'LO I nt C lock Output
Values FAI LS', ' LO E xt C lock Output Values FAI LS', and the other LO f u n ctional tests
pass, the probable cause of the fai l u re is in the sine ROM, i nterpolator and adder,
or the LO output buffers. Check the signatu res at the following poi nts using LO DSA
PATT 1 :
a. A4 TP1 6 (N DAT), A4 TP23 (S I N E), A4 TP24 (COS)
b. Adder Outputs: A4 U39 pins 8, 9, 1 1 , and 1 2.
c. Sine ROM Outputs: A4 U39 pins 2, 4, 1 6, and 1 8
d. I nterpolator Outputs: A4 U39 pins 1, 3, 1 7, 1 9
NOTf
If the LO functions properly in all modes
but fails the output value
test, the test circuits may be failing. Check
A4 U41, U42, U48, U59,
and U69.
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