HP 740B Operating And Service Manual page 52

Model 740B
Table 5-6. Changing the Padding Resistance with Jwnper Wires
Section V
Required Change In Series
Variable
Resistance To Move Meter In A
To Increase Series Resistance, To Decrease Series Resistance,
Padding
Clip Jwnper Across Add Jwnper Across
Resistor
Positive Negative
Direction Direction
R2 Increase Decrease R14 or R15 R14 or R15
R3 Decrease Increase R17 or R18 R17 or R18
R4 Decrease Increase R20 or R21 R20 or R21
R5 Decrease Increase R24 or R25 R24 or R25
R6 Decrease Increase R27 or R28 R27 or R28
R7 Decrease Increase
R30 or R31
R30 or R31
R8 Decrease Increase R33 or R34 R33 or R34
R9 Decrease Increase R37 or R38 R37 or R38
o. Depress OUTPUT pushbutton to compare 740B
output with external voltage.
p. Adjust A1R40 (REF COARSE ADJ) andA1R41
(REF FINE ADJ) as necessary to produce a null
indication on the null voltmeter 10 MV range.
This calibrates the internal 1 V referency sup-
ply for best accuracy in STD mode.
- - - - - N O T E - - - - - -
For better than specified instru-
ment accuracy in the ~VM mode
(with a slight loss of accuracy in
STDmode) the reference supply ad-
justments can be made with the
known external voltage applied to the
+ and - INPUT terminals
(~VM
mode).
Set VOLTAGE SET controls to indi-
cate first five digits of known ex-
ternal voltage. AdjustA1R40 (REF
COARSE ADJ) and A1R41 (REF
FINE ADJ) to give correct meter
indication for sixth digit with X10 4
SENSITIVITY depressed.
5-63. VOLTAGE SET DRIFT CORRECTION.
cedure (Paragraph 5-57). Refer to Figure 7-5, In-
ternal Alignment Schematic and Component Location
Diagram, for the following discussion.
5-65. The range of adjustment of each variable padding
resistor (A1R2 through A1R9) is controlled by several
series resistors. Some of the series resistors are
shunted by jwnper wires during manufacture.
5-66. If null cannot be achieved, determine if the
padding resistance must be increased or decreased
(Table 5-6). To increase the resistance, clip one of
the jwnper wires shunting one of the padding resistors
associated with the appropriate adjustable resistor
(Table 5-6). For example, if it is necessary to increase
the resistance in series with A1R2, clip the jwnper
wire shunting A1R14 or A1R15. To decrease the re-
sistance' a jwnper mustbe addedacrossA1R140r A1R15.
5-67. In some cases, both jwnper wires may already
have been clipped or removed and it is necessary to
increase the resistance in series with one of the
variable resistors. In this case, itwill be necessary
to increase the value of one of the fixed resistors.
Table 5-7, lists the recommended changes and gives
the -hp- part nwnber of the new resistor.
5-68. It may be necessary to decrease the series
5-64. The following paragraphs describe the procedure resistance even though two of the series resistors are
for changing the range of adjustment of the VOLTAGE already shunted by a jwnper. In this case, the
SET padding resistor adjustments, A1R2 through A1R9. linearizing resistor associated with the appropriate
This procedure shouldbe performedonlywhen one or variable resistor must be changed. Table 5-7 lists
more of the resistors cannot be adjusted for a null the recommended change and gives the -hp- part number
indication when performing the internal alignment pro - of the new resistor.
Table 5-7. Changing the Padding Resistors
Variable To Increase Series Resistance
-hp- Part No.
To Decrease Series Resistance
-hp- Part No.
Padding When Both Jwnpers Are
of New Resistor
When Both Jwnpers Are
of New Resistor
Resistor Already Removed, Change Installed, Change
R2 R14 to 255 kil 0698-3149 R13 to 750 kil 0757-0486
R3
R17 to 511 kil
0757-0482 R16 to 1.3 Mil 0757-0872
R4 R20 to 511 kil
0757-0482 R19 to 1.3 Mil 0757-0872
R5 R24 to 1 Mil
0698-5475 R22 to 1 Mil 0698-5475
R6 R27 to 255 kil
0698-3149 R26 to 600 kil 0698-4077
R7
R30 to 511 kil 0757-0482 R29 to 1.3 Mil 0757-0872
R8 R33 to 511 kil
0757-0482 R32 to 1.3 Mil 0757-0872
R9
R37 to 1 Mil 0698-5475 R35 to 1 Mil 0698-5475
01794-1
5-15