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Model 5065A
Circuit Diagrams, Theory, and Maintenance
A19A2 Clock Display Check
a. If display is not lit go directly to "Display Not Lit" step
b. If display is lit but not functioning correctly, proceed as
follows:
1. Check for 1 PPS signal at A19A2U1 (19). It should
be as shown o n schematic. If not, troubleshoot Driver
Circuit of A19A1U2.
2. Check operation of digit and segment drivers U2,
U3 and Q1 thru 6. If these check OK, replace U 1 . See
Note 4 o n Figure 8-26 for typical waveform.
b. Display Not Lit
1. Check voltage at A19A2(4). It s h o u l d be 5V±.5Vdc.
If incorrect, troubleshoot circuit of A19A2U1.
2 Check +12V input at A19A2(5). It should be the
same as measured at " R " terminal on A 1 9 A 1 . If not.
check continuity of +12V line from A19A1 to A19A2.
3. Substitute a new LED in one of the display posi
tions.
4. Trouble is in A 1 9 A 2 U 1 o r 2 .
Check for switching
waveforms at U1 16-12 I and 121-26). Check for switch
ing waveforms at U2 and U3 outputs. See Figure 8-26
for typical waveforms.
DS3
J14
A19 FRONT PANEL
8-70
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