HP 740B Operating And Service Manual page 53

Section V
Model 740B
Section V Model 740B
FRONT PANEL TROUBLESHOOTING TREE
IIIOLATDlG THE TROUBLE TO A llECTION
Figure 5-14. Front Panel Troubleshooting Tree
5-16
NOTES
01794-1
Table 5-8. Preliminary Checks
SYMPTOM POSSIBLE CAUSE/CORRECTIVE ACTION
Inoperative (any or all 1. Check AC Fuses.
modes)
2. Make sure Internal Alignment Switch (S3)
is in "Operate" position.
3. Check Power Supply Voltages (Figure 7-3,
Sheet 2 of 4).
Erratic Operation or Switches may be dirty. Turn instrument off;
Poor Repeatability rotate all switches several times (including
Internal Alignment Switch, 83). Switches
are self-cleaning (Paragraph 5-108).
OVERLOAD Light On Check DC Fuse. If blown, replace. If fuse
(all modes) blows again, Q1 or Q2 may be shorted.
Proceed to Main Loop Troubleshooting Tree,
step 34.
OVERLOAD Light On Normal indication. In STD mode, mV Ranges
(STD mode, mV Ranges) are inoperative (Paragraph 3 -15, step h).
Output voltage inaccurate 1. Make sure SENSE terminals are -connected
correctly (Paragraph 3 -17). Remote
Sensing must be used for remote loads.
2. Make sure ZERO control is set properly
(Paragraph 3-31).
~
VM mode inaccurate
1. Make sure INPUT Z Switch is set to
00
position.
2. Make sure ZERO control is set properly
(Paragraph 3-46, 3-47).
Unable to zero Input or 1. Recheck Internal Zero Adjustment (Para-
Output with ZERO control graph 5-44), Balance Adjustment (Para-
graph 5-46) and Meter Zero Adjustment
(Paragraph 5-50).
2. Check A10BT1 (1. 3 V minimum).
OUTPUT Indicator lighted Normal indication. OUTPUT Indicator lights
when Output Cable is not when depressed even when Output Cable As-
connected sembly is not connected. The Output Rotary
Switch (K1), however, does not energize.
Internal Buzzing when This is normal. The noise comes from the
changing Ranges or ex- Internal Current Limit Circuit.
ceeding Current Limit
Noisy meter on 1 mV Range,
Normal indication. (Paragraph 3-59, step g)
X10 4 Sensitivity
5-16
54. _rument
{ ::~~
50. Perform STD SlId
.0.
VM
{
Accuracy Tests. _ru-
ment paue8.
44. Select VIiI, 1 m V Range.
Apply I mV input. Instru- 55. See Text.
{
ment gives correct indica-
tion.
38. Select VM. 1000 V . 51. Troubleohoot A3 RaDp
Range 1000 V input. In- SwltchlDg.
strument gives correct
indication.
45. Troubleshool Range
Switching (used in VM).
48. Troubleshoot M.in Loop.
37. Remove 50 kllioad. O u t {
put monitor indicates
1000 V. OVERLOAD. 52. Troubleshoot Range
light is off. {SwItChing (used in STD).
47. Select VM. 1000 V Range.
Apply 1000 V input. in-
strument gives correct
1nd1cation.
53. Troubleshoot Main Loop.
48. Troubleshoot Function
SwllchlDg (.o.VM).
38. Select VM and check
meter indication on all
sensitivities. Meter
gives correct indications.
I V. Loop.
39. Troubleshoot Func.tion
Switching ("VM).
33.
34. Select 10 V Range, XI0
{400
i.::leshoqt Meter
SENSITIVITY. Meter
gives correct indication.
41. Troubleshoot Function
80rllcblllc
(VIiI).
32. Select STD, 1000 V
Range. 1000 V Out-
put. Coonect a 50 til
20 W load across Out-
IUt
terminals. Inatru-
ment supplies 1000 V
output.
27. Output monitor indicates
IV.
26. Select "'VM. I V Range.
Apply I V in!"t. Instru-
ment gives correct indi-
cation.
28. Troubleshoot STANDARD
{
VERNIER circuit.
21. Select VM. 10 V Range,
XIO SENSITIVITY. Apply
1 V input. Meter indica s
+1. O.
29. Troubleshoot Meter Loop.
20. Select VM, I V Range.
Apply I V input. Meter
gives correct indication.
01794-1
30. Troubleshoot Function
{
Switching ('ITD).
22. Select .6.VM. Instrument
{
gives correct indication.
31. Troubleshoot Reference
17. Select VM. Apply I V L90p.
input. OJtput monitor
indicates 1 V.
23. TrotKJleshoot Main Loop.
16. Observe meter. Meter
indicates -+ 1. O.
8. Select STD, I V Range,
{
I V output. Output moni-
tor indicates l' V.
4. Select .o.VM. I V Range,
XI0 4 SENSlT1VITY. Ad-
joet ZERO. Meter Indi-
catea 0 V. Noise < 2 J,J.V
pop (I minor division).
9. Troubleshoot Function
Switching (.o.VM).
10. Troubleshoot Function
{
Switching (STD).
5.
~1~~~Arri~~d-
just ZERO. Meter indi-
cates 0 V. Noise < 2 JJ.V
pop.
11. Troubleshoot Reference
L90p.
6. Select .o.VM, I V Ranse.{12'
~~t:I~~~.unCtion
Xl0 4 SENSITIVITY. Ad-
just ZERO. Meter indi-
cates 0 V. Noise < 2 IlV
pop (I minor division).
13. Troubleshoot Meter
L90p. { 1 8 '
~::h~f'ncllon
14. Select .o.VM, I V Range,
XI04SENSITIVITY. Ad-
{ ~':~~~~'N~ie::~~:~
[24'
~~::~e~:~~PUt
Pro-
pop.
7. select STD. 1 V Range. 19 Connect jwnper from
+
o
V output. Adjust ZERO. . INPUT
to
AI7Vl (redwire).
C:::~::;:l~rlJ~c_~.es
Noiae and offset disappear.
15. Troubleshoot M.in L90p. 25. Troubleshoot Main L90p.
2. Select STD, 1 V Range, OV
output. Adjust ZERO.
Output monitor indicates 0
V. Noi.. < 2 ~V pop.
3. (l)aerve output monitor.
Adjust ZERO. Output monl-
tor iDcUcates 0 V. Noise on
output
<
2 ~ V pop.
FAILS
7408-0-30019
PASSES
t
2. Refer to Functional DIagram, Figure 7-3. to ob-
serve overall instrument operation.
I. Uae. sensitive dc voltmeter (-hp- Model 419A)
connected to Output terminals to monitor output
voltage and noise.
3. All check. (except No. 19) should be performed
with instrument covers and shields in place.
4. Procedure.ssume.boardpluu•. cl.... Slldmaldac
good contact and power supplies are workiDc. Refer
10 Fleure 7 -3 lor .-er supply voltage. SlId lest
points.
I. Select VM, 1 V Range, In-
pulohorted. xl04 SENSl-
TJVITY. Adjust ZERO.
Meter indicates O. Meter
noise <
2 It V p-p (l minor
division).