HP 740B Operating And Service Manual page 54

Model 740B
5-69. TROUBLESHOOTING PROCEDURE.
5-70. The following paragraphs contain information on
troubleshooting the Model 740B. Before troubleshooting
the Model 740B, attemptthe Adjustment and Calibra-
tion Procedure (Paragraph 5-34). Some apparent mal-
functions can be corrected using this procedure. For
example, inaccuracy or non-linearity maybe corrected
by performing the Internal Alignment Procedure (Para-
graph 5-57).
5-71. Check Table 5-8, Preliminary Checks, for the
trouble symptom. If the symptom is not listed, the
Troubleshooting Trees (Paragraph 5-72) should be
helpful.
5-72. TROUBLESHOOTING TREES.
5-73. The Front Panel Troubleshooting Tree in Fig-
ure 5-14 consists of some fairly rapid checks arranged
Section V
to isolate trouble to a major loop and occasionally
traces trouble to a specific circuit. In addition, the
Front Panel Tree checks most of the Range and Func-
tion Switching.
5-74. The Main Loop, Meter Loop and Reference Loop
Troubleshooting Trees (Figures 5-15, 5-16, 5-17) can
be helpful in isolating trouble to a specific circuit with-
in these major circuits.
5-75. To use the Troubleshooting Trees, decide if
step 1 passes or fails, and proceed to the next step
along the appropriate branch of the tree. The steps
in each tree are explained in detail in a table adjacent
to the tree. The checks outlined in the trees do not
usually isolate trouble to a specific circuit component.
Once the trouble is isolated to a specific circuit, ad-
ditional checks will probably be required to isolate the
faulty component. Waveshapes and operating voltages
shown on the schematic diagrams may give additional
help.
Table 5-9. FRONT PANEL TROUBLESHOOTING
1. A correct indication shows that the Main Loop and
Meter Loop are probably working.
2. A correct indication shows that STD mode Func-
tion switching is probably working and that the
Reference Loop is relatively noise free.
3. A correct indication shows that the Main Loop is
not causing the noise or offset shown on the 740B
meter.
4. A correct indication shows that the Main Loop,
Reference Loop and Meter Loopare all relatively
free of noise and offset.
5. A correct indication shows that the Reference
Loop is probably not causing the noise or offset.
6. A correct indication shows that the Meter Loop is
probably not causing the noise or offset problem.
7. If the output is free of noise and offset in STD
mode, the Main Loop is probably not at fault.
8. A correct indication verifies that the Reference
Loop and Main Loop are operative.
9. Since trouble occurs only in e:.VM, the trouble is
most likely in e:.VM Function switching. Possible
trouble areas: Deck SlH(F), SlI(F) and SlG(R)
of Range/Fwlction Switch, Sl (Figure 7 -3).
10. Trouble is probably in STD mode Function switch-
ing. Possible trouble areas: Deck SlI(F), SlH(R)
and SlH(F) of Range/Function Switch, Sl (Figure
7 -3).
11. Follow procedure in Reference Loop Trouble-
shooting- Tree (Figure 5-17).
12. Function Switching used in VM is probably at fault.
Possible Trouble areas: Deck SlI(F) and SlH(R)
of Range/ Function Switch, Sl (Figure 7-3).
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13. Since the Main Loop is not causing noise or off-
set and the trouble occurs in both VM and e:.VM,
the problem is most likely in the Meter Loop.
Follow procedure in Meter Loop Troubleshooting
Tree (Figure 5-16).
14. A correct indication shows that the Main Loop is
capable of operating properly.
15. Since noise and offset are present at Output ter-
minals in all modes, the trouble is most likely
in the Main Loop. Follow procedure in Main
Loop Troubleshooting Tree (Figure 5-15).
16. A correct indication shows that the Meter Loop
and the Standard Vernier Circuit are functioning.
17. A correct indication shows that the Main Loop is
operating.
18. VM mode Function switching in Main Loop is
probably at fault. Possible trouble areas: Deck
SlG(R) and SlH(F) of Range/Function Switch, Sl
(Figure 7 -3).
19. If noise and offset disappears, the Main Loop is
not at fault.
20. A correct indication verifies proper operation of
the Input Protection Circuits, VM mode Function
switching and the Meter Loop (Xl Sensitivity).
21. These settings duplicate the Meter Loop operation
attempted in step 16. A correct indication shows
that the Meter Loop is not at fault.
22. A correct indication in e:.VM shows that the Re-
ference Loop and Main Loop are probably notat
fault .
23. Follow procedure in Main Loop Troubleshooting
Tree (Figure 5-15).
5-17