HP 740B Operating And Service Manual page 55

Section V
Table 5-9. FRONT PANEL TROUBLESHOOTING (Cont'd)
Model 740B
24. Troubleshoot Input Protection Circuit (Figure 7 -3).
Possible trouble: Bad A9Q1, A9DS2 or A9V2.
25. If noise and offset are still present at Output ter-
minals' trouble is probably in the Main Loop.
Check Range/Function
swit~hing
between A17V1,
V2 (Modulator) and A3 pin 1; also check Range/
Function switching associated with the Main Loop
Feedback Divider (p/o A9). If trouble cannot be
found, follow procedure in Main Loop Trouble-
shooting Tree (Figure 5-15).
26. A good indication verifies proper operation of
t!.
VM Function switching and Meter Loop operation
on the higher Sensitivities.
27. A correct voltage at the Output termipals verifies
proper operation of the Main Loop.
28. The trouble is probably in the Standard Vernier
Divider, S9A (Figure 7-3). Also check for con-
tinuity (STD mode) between pins 7 and 8, deck
SlI(F), of Range/Function Switch, S1.
29. Follow procedure in Meter Loop Troubleshooting
Tree (Figure 5-16).
30. STD mode Function switching is probably at fault.
Possible trouble areas: Deck S1J(F), S1H(R),
SlH(F) and SlI(F) of Range/Function Switch, S1
(Figure 7-3).
31. Follow procedure in Reference Loop Trouble-
shooting Tree (Figure 5-17).
32. A correct output verifies proper operation of the
Main Loop on the 1000 V Range.
33. A correct indication verifies proper t!. VM Func-
tion switching in the Main Loop.
34. A correct indication shows that VM mode Func-
tion switching is probably not at fault.
35. A correct indication shows that the Input Pro-
tection Circuit is not at fault.
36. A correct indication shows that the Main Loop
works properly in VM mode, 1000 V Range.
37. A correct output with no load indicates low gain
or Current Limit problems in the Main Loop.
38. Correct indications verify proper operation of
the Meter Loop.
39. t!.VM
Function Switching in the Main Loop is
probably at fault. Possible trouble areas: Deck
SlH(F) and SlG(R) of Range/Function Switch, Sl
(Figure 7-3).
40. Follow procedure in Meter Loop Troubleshooting
Tree (Figure 5-16).
5-18
41. Check deck SlIeR) pins 4 and 5 for contin'lity in
VM mode (Figure 7 -3). If trouble cannot be found,
follow procedure in Meter Loop Troubleshooting
Tree (Figure 5-16).
42. VM mode Function switching is probably at fault.
Possible trouble areas: Deck SlG(R), S1H(R),
SlH(F) and SlI(F) of Range/Function Switch, S1
(Figure 7 -3).
43. Since the trouble occurs in both VM and
t!.
VM
modes, the trouble is probably in the Input Pro-
tection Circuit (Figure 7 -3). Possible trouble:
Bad A9Q1, A9DS2 or A9V2.
44. A correct indication shows that the Main Loop
provides the necessary increased gain on the m V
Ranges.
45. Range switching used .only in VM and t!.VM is
probably at fault. Possible trouble area: Deck
S1C(R) of Range/Function Switch, S1 (Figure 7-3).
46. Perform Loop Gain Check (Paragraph 5-76). If
instrument passes, proceed to step 49 in Main Loop
Troubleshooting Tree (Figure 5-15).
47. A correct indication shows that the Main Loop is
capable of functioning on the 1000 V Range.
48. t!. VM Function switching in Meter Loop or Re-
ference Loop is probably at fault. Possible
trouble areas: Deck SlI(F) and SlH(R) of Range/
Function Switch, Sl (Figure 7 -3).
49. Follow procedure in Meter Loop Troubleshooting
Tree (Figure 5-16).
50. STD and t!. VM Accuracy tests are outlined in the
Performance Tests section (Paragraph 5-5).
51. Range switching used only on the m V Ranges may
be at fault. Possible trouble areas: Deck SlB(F)
and SlF(F) of Range/Function Switch, Sl (Figure
7-3). If trouble cannot be found, proceed to step
2 in Main Loop Troubleshooting Tree (Figure 5-15).
52. Range Switchingused in STDmode is probably at
fault. Possible trouble areas: Deck SlB(R) and
SlC(F) of Range/Function Switch, Sl (Figure 7 -3).
53. Trouble is probably in the High Voltage Section of
the Main Loop. Proceed to step 16 in Main Loop
Troubleshooting Tree (Figure 5-15).
54. If instrument passes all of the previous checks,
all of the major loops are functioning properly.
55. If the instrument fails one or more of the accuracy
tests, the trouble is probably associatedwith cir-
cuits or switching peculiar to that test. For
example: If inaccuracy occurs only on the 100 V
Range and only in STDmode, the trouble may be
in Range Switching for the 100 V Range that is
used only in STD (Deck SIB (R) of Range/Function
Switch, S1).
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