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Section
V
Paragraphs
5-23
to
5-35
b. Set Sampling Oscilloscope controls as follows:
TIME SCALE...............
20ns/cm
VERNIER.........020ceeee
CAL
'
TIME
SCALE
MAGNIFIER...
.X2
CHANNEL
SELECTOR.......
Channel A
SENSITIVITY............026
50mV/em
c. Move the trigger pulse to the center of the CRT.
The pulse amplitude should be 2 V or more.
d. Adjust Oscilloscope plug-in sensitivity VERNIER
for a full screen picture.
Observe the pulse width at
50% amplitude points.
The pulse width should be 10ns
(1 cm).
e. Change Model 211B TRIGGER POLARITY switch
to positive.
Pulse should be positive and same speci-
fications asin steps
c and
d apply.
5-23.
POWER
SUPPLY
5-24. If the power supply circuits are inoperative,
check the power
cord connection and line fuse F 1.
Refer to the schematic for other components in the
ac portion of the power supply circuit.
All dc voltage
measurements,
typical values indicated on the sche-
matic, should be made with respect to chassis ground.
Adjustments can be made after the top cover of the
211B has been removed.
a. Adjust
R18
for
-20 V
b. Adjust
R26
for
-70 V
5-25.
TROUBLESHOOTING
5-26.
To locate trouble in the 211B,
start with a
thorough visual inspection and then proceed to
electrically check out as necessary.
During the visual
inspection look for burned or loose components,
loose
wire connections,
or any other similar
condition
which suggests a source of trouble.
Repair any faulty
component or connection that is isolated during the
visual inspection and check instrument performance
before
continuing to troubleshoot the instrument.
5-27.
If no obvious fault is located during the visual
inspection proceed with the electrical check out. Use
the block diagrams in Section IV as an aid in isolating
the trouble to a particular circuit.
5-28.
REPAIR
AND
REPLACEMENT
5-29
Repair of the Model 211B consists basically of
replacing defective components
located during trouble-
5-6
Model
211B
shooting.
The following paragraphs provide informa-
tion on the identification and location of all components
in the Model 211B,
and basic considerations when
repairing etched circuit boards.
If satisfactory
operation or repair cannot be accomplished,
contact
your nearest Hewlett-Packard
Sales/Service Office
(adresses given at rear of this manual).
If shipment
of the instrument to the Sales/Service Office for
repair is recommended,
refer to Paragraph 2-4 for
repackaging information.
Refer to Section VI for part
numbers
of replaceable parts and ordering instructions.
5-30.
COMPONENT
IDENTIFICATION.
5-31.
All electrical components in the Model 211B
are identified on the schematics with a reference
designation.
Location of components mounted on etched
circuit boards or switches is provided in the compo-
nent location figures.
All electrical components
not
mounted on etched circuit boards or switches are
identified in Figure
5-10.
5-32.
To help with proper replacement of semicon-
ductors,
the emitter or cathode connection is
identified by a small dot etched on the circuit board
beside the connection point.
5-33.
SERVICING ETCHED CIRCUIT BOARDS.
5-34,
The Model 211B has etched circuit boards
which are plated-through type. When servicing this
type of board,
components
may be removed
or
replaced by unsoldering from either side of the board.
When removing large components,
such as potentio-
meters,
rotate the soldering iron tip from lead to
lead while applying pressure to the part to lift it from
the board.
Service Note M-20D
contains additional
infirmation on the repair of etched circuit boards,
however,
the important considerations
are as follows:
a. Do not apply excessive heat.
b. Apply heat to component lead and remove
lead
with a straight pull away from board.
c. Use toothpicker or wooden splinter to clean hole.
'd. Do not force leads of replacement
component
into holes.
5-35.
If the plated metal surface (conductor) lifts
from the board,
it may be cemented back with a quick-
drying acetate base cement (use sparingly) having
good insulating properties.
An alternate method of
repair is to solder a good conducting wire along the
damaged area.
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