Star Tech Journal

8
S*TJJuly1981
ANALYSIS (PART 3)
BY JIM SNEAD
GENERAL MANAGER
ELECTRONICS DIVISION
KURZ-KASCH, INC.
DAYTON, OHIO
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In the above circuit we notice a 12 MHZ clock which is divided by 2 by E9. This 6 MHZ square wave is used to clock the horizontal divider chain
(E9, D9, C9, and B9). Derived from this chain is H blank (B9-6) and H SYNC (B9-9).
H SYNC is used to clock the vertical SYNC Divider Chain (CB, D9, EB, and E7). V Blank, V Reset V Blank, and V SYNC are outputs of E7.
These SYNC circuits are a "piece of cake" to obtain signatures from and to test using SA. Here's all you have to do:
HORIZONTAL SYNC
A. Use D9-2 as CLOCKJ
Use 9-11 as START/STOPf
Read and record signatures on D9 pins 7, 14, 13, 12, 11 and 15. If these signatures are correct proceed.
B. Use C9-2 as CLOCK..F
Use C9-11 as START/STOP..F
Read and record signatures on C9 pins 10, 9, 14, 13, 12, 11 and 15, and E7-9.
C. After the signatures are obtained on all above pins in steps A & B leave SA connected as in step B and read and record signatures from
B9, 2, 3, 4, 5 & 6. Pin 6 gives you H blank.
Now read and record signatures from B9-B, 9, 11, 12 and 13. Pin 9 gives you H SYNC.
If H SYNC is OK, you can proceed to:
VERTICAL SYNC
A. CLOCK CB-2 ../"
START/STOP CB-11.J
Read and record signatvres on CB pins 14, 13, 12, 11, 15 and 9. If these signatures are OK, proceed.
B. CLOCK DB-2 f
START/STOP DB-11.f
Read and record signatures on nB-9, 1 O, 14, 13, 12, 11, 15
EB-pins 1, 2, 3, 4, 5, 6, 7, 9, 10, 11 , 12 & 15
E7-pins2*, 3,4, 5, 6*, 7, 10, 11 *, 12, 13, 14 & 15
You have fully documented this SYNC Chain.
The sequence of the SYNC circuit is CLOCK-H SYNC-V SYNC, all in series. Bad clock can kill everything, H SYNC can kill V SYNC.
So start at the beginning.
A quick check can be made by connecting the Signature Analyzer to:
C9-2 CLOCK J
C9-11 START/STOPJ
Read signature at B9-9, if correct you have horizontal SYNC.