HP 3562A Service Manual page 495

MOD E L 3S62A
3 . Phase Val ue Fai l u res
The p hase value is read from the phase l atchs (A4 U23, U27). If the ph ase val ue fai l s,
the output value is p robably fai l i n g too. ( H owever, if the fai l u re message is 'LO I nt
C lock P hase Values FA I LS', ' LO E xt C l ock P h ase Values FAI LS' and the other LO
self-tests pass, the pos s i b l e cause of the fai l u re is the phase l atchs 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 ( i n part B) as fol lows
to isolate the "fa i l u re:
LO DSA PATT 1
a. Start by chec k i ng the phase accu m u l ator outputs (A4 U S).
b . I f the p hase accu m u l ator output signatu res are correct, check A 4 U 2 2 a n d U26.
c . Check A 4 U68, U S6, a n d US8 i n t h e control a n d t i m i ng c i rcu its. T h e n c heck A4
U1 9, U31 , and U36 p i n s 2, 3, 4, 1 0 through 1 9 i n the system b u s i nterface.
d . I f any of the signatu res i n step c are wrong, c heck the i np u t s ignals to the
components. If the i n puts to the components are correct, the fai l u re is most l ikely
caused by the p hase acc u m u l ator.
LO DSA PATT 2
The phase accu m u l ator feeds its output back to the i n put. LO DSA PATT 2 breaks
this feed back loop. Start by checking the signatu res of A4 U1 1 and U1 6. Check the
s ignatu res of the other components i n the phase accu m u lator by moving forward and
back from A4 U1 1 and U1 6.
4. Output Val u e Fai l u res
The outp u t val ue i n the exc l u s ive OR of the S I N E and COS outp uts w h i c h are sh ifted
i nto the LO output buffers (A4 U41 , U42). If the fai l u re message is 'LO I nt C lock Output
Values FAI LS', ' LO E xt C lock O utput Val ues FA I LS', and the other LO f u n ctional tests
pass, the probable cause of the fai l u re is in the s i n e ROM, i nterpolator and adder,
or the LO output buffers. Check the signatu res at the fol l ow i n g poi nts u s i ng LO DSA
PATT 1 :
a. A4 T P1 6 (N DAT), A4 T P23 (S I N E), A4 TP24 (COS)
b. Adder O utputs: A4 U39 p i n s 8, 9, 1 1 , and 1 2 .
c. S i ne ROM Outpu ts: A4 U39 p i n s 2, 4, 1 6, and 1 8
d. I nterpo l ator Outputs: A4 U39 pins 1, 3, 1 7, 1 9
If the LO functions properly in all modes
test, the test circuits may be fa iling. Check
and U69.
NOTf
but fails the output value
A4 U41, U42, U48, U59,
S E RV I C E
8-45