HP 740B Operating And Service Manual page 60

Section V
METER LOOP TROUBLESHOOTING TREE
NOTES
1. All measurem ents should be made with reapect
to
W
2. Meter Loop schematic and camponSDt location diagram a
are shown In Figure 7-6.
3. Put A2
00
a printed circuit board extender to
monitor voltages and waveshapes at board pins.
4. a.serYe waveshape at A2
pin L Reduce 740B Input
- - voltage until waveahape at
A2 pin I Is appl'(lKlmately
50 m V p - p. Wavesha pe at
collector 0( A2Q3
> 5 V P - p.
Model HOB
8. Reduce Input voltage until
wavewpe at collector of
A2Q3 la I V P - p. Wave-
shape at A2TP8 Is I V P - P
or greater.
8. Troubleshoot A2QI. Q2.
Q3.
12. Depre.. Xl02 SENsrrlVITY.
Wan8hllpe at A2TP8 > g V
P
-po
U. Tr.....laalooot A2Q4. QS
aDd QU.
16. Depr... Xl SENSITIVITY.
Apply + 1 V to Input ter-
mlnala. Remon jum per
from AIM. lIeter Indi-
eatea + 1 V withIn 2
MCoIIda.
17. Tr.....leshoot A2Q4. Q5.
QII aDd seoaltlvlty Gain
9Ir1tch1n& .
18. Reverae Input polarity.
Meter indicate. -1 V.
19. Connect jumper from A2
pin 12 to AI6V2 (white wire
Problem disappears,
20. Check other seoaltlvlty
poaltlooa. U tr.....le oceura.
troubleshoot correapoDdlng
sensitivity Swltehlng and
S2RI through S2R4.
21. Troubleshoot Meter DrIver
(A2Q8 through QlI).
22. Troubleshoot Feedback
Switching.
23. Troubleshoot Meter Driver
(A2Q8 through QlI) aDd M1.
2. Wan8hllpe at A2 pin 10
>
I V 10. Troubleshoot Demodulator
p-p.
(AIIV2/V4).
PASSES
t
5. Wave8hllpe at A2TP8
>
8 V
14. Trouble_ AJQ4. QI
p-p. udQlI.
1. select VM. 1 V Range. 1 V
Input. Xl SENSITIVITY.
COIlDect a jumper from AI6V2
(white wire) to
W.
Wave-
shape at A2 pin 1 > O. 5 V p-p.
I. Troubleshoot lloilulator
11. Waveahape at collector of
(AllYl/VI).
A2Q3
>
5 V p-p.
I
FAILS
2. +1 V present III AllYl
15. Trodlle_ A2QI. Q2
(terminal ne~ ..t AU).
udQl.
7408-0-30021
Figure 5-16. Meter Loop Troubleshooting Tree
5-24
7,. Troubleaboot IIlIIn Loop.
01794-1