Repair And Replacement; Adjustment And Calibration - HP 6177B Operating And Service Manual

Table 5-10. Troubleshooting Constant Current Comparato:- anc Iviain Erro, !\r:1plifier-
I
STT'P
.cL.
ACnOr;
I
HESPONS::::
I
PROBAEL;-: CAUSE
,
PI\RT
,
HIGH OUTPUT CURR;::J\T
h .
1 Check operation
0:
Z 1 by
I
c. Output Cl..!rrent cecreases.
I
c. Zl dsfective.
switching Zl and Z2.
Output current
high. b,
Check 0191". for-
~.
remE!lnS
open, 019B :or
short, 02J for
I
I
open, VRIO for
shor-t. CR3C open
,
CR27, GR28 sr.ortec.
I
I
I
,
PART
B.
L010/ OUTPUT CURREIC
1
I
Check operation of
Z 1 by s\vitch- a. Output current increa ses. a.
Z1 defective.
ing Zl and 22.
):.
Output current remains low. b. Check Q19A for
short , Q195 for
open, 021 Ior
short, VR10 for
i
open,
5-48 REPAIR AND REPLACEMENT to free adjustment screw from meter suspension. If
pointer moves, repeat steps (b) and (c).
5-49 Wnen replacing a defective component, reier
to Section VI for component part number and de-
scription. Since too much heat could lift the cop-
per circuitry off of
a
printed circuit board, a iow
power soldering iron (50 Vv'atts maximum) shoulc be
used. Solder suckers make replacement of compo-
nents easier and cleaner. especially when multi-
lead parts are being used; and for this reason, are
highly recommended. Use only high quality rosin
core solder when repairing printec circuit boards.
5-50 ADJUSTMENT AND CALIBRATION
5-51 Adjustment and calibration may be required
after performance testing. troubleshooting, or re-
pair anc. replacement. If more than one adjustment
must be performed, the sequence of adjustments
presented in the following paragraphs should be
followed.
5-52 METER ZERO
5-53 Proceed as follows to mechanically zero the
meter:
a.
Turn off instrument (after it has reached
normal operating temperature) and allow 30 seconds
for all capacitors to discharge.
b. Insert sharp pOinted object (pen point or
awl) into the small indentation near top of round
black plastic disc located directly below meter
face.
c. Rotate plastic disc clockwise (cw) until
meter reads zero, then rotate
CON
Slightly in order
5-14
5-54 AMMETER TRACKING
5-55 The ammeter circuit is adjusted to within
±2%, (for full scale readings) at the factory and
nonnally does not require adjustment unless a
component in the meter circuit is replaced.
5-56 To calibrate the ammeter, proceed as follows:
a, Replace any'
mete~
circuit jumpers (lor 2;
see schematic) that have been removed previously,
at the fa
ctOf'/.
b. CODY1ect test ·setup of Figure 5-3 (external
range SWitch and medium-low range load reSistors
can be eli::linated, if desired).
c. Turn VOLTAGE control fully clockwise, set
range switch to highest current range, and connect
+ leae of differential volt::leter to RS 1.
C. Set meter switch to AMPS and adjust CUR-
RENT control
until
front panel meter reads exactly
the maximurr, rated output current.
e. Observe reading on differential voltmeter.
If it is between 0.981 and 1.019Vdc (Model 6177B)
or 2.452 and 2.548Vdc (Model 6181B) leave jumpers
1 and 2 connected and operate normally.
f.
1£ differential voltmeter reading is be-
tween 0.941 and O.981Vdc (Model 6177B) or 2.345
and 2.452Vdc (Model 6181B) remove jumper number
1 (across R89). Reading should now be within nor-
mal limits of step (e).
g. If differential voltmeter reading is be-
tween 0.905 and 0.941Vdc (Model 61778) or 2.252
and 2.34 SVdc (Model 6181B) remove jumper number
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