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I
- . R-
E INFORMATION FRO ACKARD
MARCH-APRIL 1974
TROUBLESHOOTING
LOGICALLY A
by Neil Neilson
Problem solving is a continually daily
problem for most people. The person
who is well organized in his approach
to problem solving is much more effi-
m
cient than t w who are not.
h
Organized o not, most of us use some
r
we' in solving our problems.
Such problems arise when a techni-
cian I faced with troubleshooting an
s
unfamiliar electronic instrument. Here
successful problem solving techni-
ques provide him with the most effi-
cient and economical way of repairing
the instrument. Such an approach to
troubleshooting is described below.
The first part of the procedure con-
tains a set of questions to be ans-
wered by the technician.
Queslion 1: What is the device
and what is it supposed to do?
The answer is located in the specifica-
tions for the unit under test. Un- Where should the next me!a8untment be made? Having a loglcalprocedure will help you flnd
the fallure wlth the least number of measurements. This artfcle Wls how.
derstanding what the unit does makes
the selection of test equipment easier. documents from the manufacturer. block or arcuit within the functional cir-
Question 2: Does the instru- Another technician is also a good cuitry. With the symptom determined,
ment do what it was designed to source of information. This is where the the abnormal path of circuitry is identi-
do? professional stands out-he (or she) fied. The technician can now isolate
Most service manuals contain a de- knows that it is impossible to have all the problem with a technique called
tailed performance test procedure. If of the answers and willingly asks for "bracketing." Bracketing is simply a
no procedure is available, use the spe- help.
cifications and devise your own. If the
unit under test meets specifications, it If no one else has seen the problem,
is a good indication that you need he must solve it himself. At this stage,
more information or that the unit has he applies the Rules of Logical
no problem. Search for more informa- Troubleshooting. This consists of
tion! Question the user. Heat, cool and "milking" the front panel for all symp-
shake the unit to determine if the prob- toms available. Are lights lit? Rea-
lem is intermittent. But, by all means, douts active? The symptoms are next
d i w v e r the problem. sorted by functions-trying to localize
e Question 3: Has anyone seen
the problem before?
The answer can be found in several
the fault to a particular function. Many
times this can be done by using the
switches on the front panel. With prac-
tice, the technician can become quite
swrces: troubleshooting trees in the skilled at isolating the fault to a func-
senrice manual, service notes, or other tion and sometimes to a particular
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TROU6L ES H 00 TING TIP
use a technique called "half-splitting."
The main principle of half-splitting is
a
that a check is made at the midpoint of
the remaining part of the circuit that
has not yet been checked.
Looking back at Figure 1, we know
that there is no audio output (point E)
and we suspect that a signal exists at
point A (we know for certain that one
output of the detector is ok because of
the signal strength meter reading).
Now what???
FIGURE 1. RADIO RECEIVER We should measure at point C be-
cause this is halfway between the ab-
circuits from the antenna terminals to normal path. If the signal at point C is
means of establishing the broad limits
the detector are probably good (since ok, the trouble is isolated to either the
around the areas to be tested. For ex-
the signal strength meter is usually audio power amplifier or the loud-
ample, if you connect a signal to the an-
driven from one output of a detector). speaker. A measurement at point D
tenna terminals of a radio receiver and
Therefore, the problem is now isolated would indicate the defective area. Ad-
hear no output in the speaker, you
to the audio section. We also know ditional measurements may be
know that the problem exists some-
where between the antenna circuits that at least some of the power sup- needed to determine the defective
and the speaker cone (Le. the entire plies are working, and this is valuable component.
receiver). See Figure 1. If, however, information. Figures 2 through 5 display circuitry
you notice that the signal strength other-thana linear path and the trouble-
meter shows a strong indication, the As checks are made, the area be- shooting rules utilized for each. As-
tween the brackets becomes smaller
CHECK PT OF DIVERGENCE. IF OUTPUT IS and smaller until the defect is pin- MODIFY FEEDBACK
NORMAL, CHECK DIVERGENT PATHS. pointed. Bracketing defines the limits IF OUTPUT CHANGED, TROUBLESHOOT
of the defective circuit and we must FEEDBACKPATH
make measurementsto further isolate IF OUTPUT UNCHANGED, TROUBLESHOOT
Test 1 4 .--+ the problem. LINEAR PATH
1;
7
In our example, we know the problem Test 1
n
4 NO OUTPUT
exists somewhere between the detec-
tor and loudspeaker. Where should
we make our first measurement? One
technique used all too often is to mea-
1,l-i OUTPUT
FIGURE 2. DIVERGENT PATH
sure point A (to verify that the detector
is really working) and then to make
measurements at B, C and D until the
defective stage is isolated. While this
method works, a faster approach is to
w
+ - + - BOTH SIGNAL PATHS.
1
Test 1
Test 3 1 4
+ OR `--j
-
Test 2 Test 1
+ - + OUTPUT
-
CHECK EACH INPUT: IF OUTPUT 1 NOR-
s CHECK ONE INPUT: IF OUTPUT I NORMAL,
S
MAL, CHECK CONVERGENT STAGE CHECK CONVERGENT STAGE
FIGURE 3. CONVERGENT PATH FIGURE 5. SWITCHING PATHS
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1
SERVICE Tip / L I T E R A TU RE
I'
I circuits shown measurement to make. Generally APPLICA~ON NOTES-
t, Test 1is made. speaking, the technician should start
remaining portion of the dr- with the most general measurement A LEARNING AaE FROM
der test is a linear path. In this of waveform and proceed to the more HEWLETT-PA0
caw, the half-splitting technique can specific measurements of voltage and
be readily used to troubleshoot the resistance. A series of publications are available
rest of the circuit. Such is the modis operendi of a Logi- from HP that may help you obtain
Discovering where to measure is only cal Troubleshooter-knowing where to more benefit from your HP purchases.
half of the troubleshooting techniqu- find information, what type of measure- Many Hewlett-Packard engineers and
the other`half is knowing what type of ment to make and where to make it. customers have collaborated in pre-
paring Application Notes, HP publica-
tions that give detailed information on
selected subjects.
Neil Neilson is the Technical
Staff Manager for Customer Service Some Application Notes are tutorial in
Center at Mountain View. His re- nature, while other describe very s p s
sponsibilities include a variety of cific "how to" procedures.
support functions such as Computer We have selected several Application
Tes ustomer Service Notes that may be of interest to ser-
win Technical Train-
vice personnel.
mg
n.
Neil enjoys a liwrely game o golf
and the sport of hunting.
f -
Time lntewal Averaging AN 162
This AN provides the basic theoretical
foundation of time interval averaging,
showing how this technique pro-
vides such significant improvement in
accuracy and resolution.
ELECTROMC TEST CARD AVAILABLE
-
Noise Figure Prlmer AN 57
This application note discusses noise
EQUIPMENT CATALOG FOR MODEL 3489A . figure and explains how it can be mea-
sured.
FOR TECHNICAL DATA PUNCH -
Selecting the Right DVM AN 158
EDUCATION A troubleshooting aid is available for This is a guide to help the user select
diagnosing a 348914 Data Punch. A the right DVM to match his application
Test Card, identified by Model with the various DVM characteristics.
A new 24-page catalog from Hewlett- Number 3489A-L10, connects directly Techniques for Digital Trouble-
Packard describes test and measur-
ing equipment appropriate for techni-
to the BCD Input of the 3489A and
simulates a typical Data Source. It will
-
shooting AN 163-1
be extremely useful in isolating mal- This covers the fundamental differ-
cal education. Student use of this
equipment provides excellent prepara- functions to the data source or the ences between discrete analog cir-
cuits and those built from digital
tion for what will later be encountered 3489A.
IC's. An analysis of the failure
in science and industry. Among the Two separate program modes are pro- modes of digital IC's suggest an
newer items is a laboratory to teach di- vided: (1) the identification of indivi- algorithm which can be used with
gital logic, complete with texts and dual BCD input columns vs. output
workbooks. Instruments include volt- HP's IC Troubleshooters to signifi-
characters; (2) the ability to externally cantly increase the efficiency of
meters, counters, oscillators, pulse toggle in any 8421 input code in all
and function generators, and re- people repairing digital circuits.
BCD input columns. In addition,
corders. the control logic and most of the inter- Sampling Oscillography AN 36-
Video tape training courses on transis- nal formatting may be checked with This note explains the theory be-
tors, digital electronics communica- this Test Card. Altogether, this Test hind sampling oscillography, in-
tions, and instrument technology are Card will provide a method to perform cluding sampling efficiency vs
offered, and a listing of available appli- a complete operational check of the frequency response.
cation notes on useful measurement 3489A Data Punch.
techniques is given. The test board, which comes com- One copy of an Application Note is
"Electronic Test and Measuring Equip- plete with instructions, has a U.S. available free of charge; just check
ment for Technical Education" is avai- price of $50. To order your 3489A- the desired Application Note num-
lable without cost. Please contact your L10, please contact your local HP ber in the space provided on the
local HP office. office. order form on the last page.
OWN A 8660A OR provements and changes are made Occasionally several changes may be
regularly. (These are indicated by a recommended on a product and for
8660B??? change in the serial prefix.) convenience in obtaining parts, all the
required parts plus installation instruc-
Some design changes made on units tions are available from HP by order-
currently being manufactured are ing one part number.
Hewlett-Packard attempts to provide recommendedfor inclusion in products
the best solution to your measurement already in use. A Service Note is writ- Hewlett-Packard is offering a free
problem. Products undergo almost ten describing the recommended Field Update Kit to any owner of an
constant evaluation for possible im- modification. 8660A or 86608 Synthesized Sig-
nal Generator with serial prefix 1349A
and below. The kit includes, among
other things, a new larger exhaust fan
assembly for better cooling of the in-
strument. Complete installation in-
structions are also provided. It is ex-
pected that the improved cooling will
increase the long term reliability of the
equipment. The kit Part Number is
08660-60273 to update a standard
(50-60 Hz) instrument. If your instru-
ment is designed for 50-400 Hz power
line operation (option 003), you need
kit 08660-60274 instead. Check the
rear panel of your instrument for an
"Option 003" label. Either kit may be
obtained free of charge through your
local HP office by indicating the kit
number and the modeland serial num-
ber of the unit in which it is to be in-
3
stalled. Installation is straight-forward
and should present no problem to elec-
Several minor modifications can be made on your 8660A or 86608. tronic service personnel.
RACING QUIZ SOLUTION Car #3 did not finish in 1st or 2nd placeThe winning car could have been la-
(statement e) or in 3rd place (state- beled #2, #4, or #5. The 2nd place car
ment 9). Therefore #3 came in last. could have been #4 or #5 and the 3rd
Successfully solving the racing quiz in place car could have been #2, #4 or
the last issue requires use of the skills The American did not finish in 4th place #5 (statement 9).
-
normally required for successful ser- (statement j), nor in last place in the The American was not driving #2
vice w0rk-a logical approach and Chev (statement a). Therefore the
some ingenuity. American came in 3rd. That leaves the (statement m) and was not driving #4
German and the Japanese. The Ger- (statement n). Therefore he was driv-
Let's start with the table and fill in the finiske~l in ar;l~e ing car #5.
known Chev in 5th place since the Japanese cannot drive the Thus the second place car is #4 and
and Italian the winner. That places the Datsun (statement a). that leaves #2 the winner.
Englishman in second place since he
beat three others (statement 0).
TheFiat must be in 3rd or 4th place
(statement 0).Since the Datsun fin-
ished behind the Fiat (statement b), the
Datsun must have finished in 4th place
and the Fiat in 3rd place. That makes
the Datsun labeled #1 (statement 0).
There are now two cars not placed, the
Triumph and the VW. The Englishman
cannot drive the Triumph, and there-
fore he must have driven the VW. Thus
the Triumph won the race (a).
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' .-'
NEW SERVICE NOTES B
B --.
t
o
Here's the latest listing of Service
Notes available for Hewlett-Packard
products. Service Notes contain infor-
mation that will help you get the most
out of your purchases.
Many times design changes or other
191A N WAVEFORM MONITOR
M A - 3 All Serials. Required vertical amplifier
balance procedure.
419A DC NULL VOLTMETER
419A-3C Serial numbers 838-01275 and below.
Ammeter modlficationkit. HP Part No. 00419-&4301.
4778 THERMISTOR MOUNT
T
h
34702A-1/34740A-1/34750A-l Serial numbers
1213A-03935 and below. Modificationto reduce
zero offset.
m
34740A DISPLAY
34750~ s u y
m
34702A-l/34740A-1/34750A-l Serial numbers
1304A-00750and below. Modificationto reduce AC
zero offset
improvements are made in products 4778-2 All Serials. RF connector assembly and 3475OA-2 Serial 1304A-00750 and below.
currently being manufactured. HP of- thermistor assembly replacement. Fallwe of the -12 Volt Power Supply.
ten recommends including these 367OA NETWORK ANALYZER
changes in products previously sold; 1 3 3 1 x-Y~
~ msPLAy
357OA-1 Serial numbers 1251-45 and below.
1331NC-5 All Serials. Improving reliability of cd- Improvedtemperature stability board kit.
this is done by writing a Service Note limator connection. 357OA-2 All Serials. New 03570-88555 log amplifier/
for the product. 1331C-2 Serial prefix 1318A and below. lntermlttent 3570-66556 output buffer boards and adjustment
erming. procedures.
357OA-3 A Serials. Rsplecsment parts changes.
H
Service Notes for your instruments 1401A DUAL TRACE AMPLIFIER
357OA4 All Serials. New 03570-88551 (50 ohms)
can be obtained by using the Service 1401-2 All Serials. Replacement for HP p/n 68558 (75 ohms) input amplifier and adjustment
1850-0103.
Note Order Form. Remove the order procedures.
form and mail it to the HP distribution 1703A OSCILLOSCOPE
1703A4 Serials prefix 133lA and below. Brown-out 5300A FREQUENCY COUMER MODULES
center nearest you. European cus- and transient LVPS modification.
It 5300A-3 This sewice note applies to modules 5301A.
tomers should mail it to this address: 1703A-5 All Serials. Improved single sweep resh 5302A,53@3B, =A, =A, 5307A, 531OA,
operation.
5311A. All Serials. ModiRcationto ensure proper
Hewlett-Packard S.A. 17078 OSCILLOSCOPE safety ground.
Central Mailing Department 17070-1 Serial preRx 1325A and below. Brown-out S308A MULTlMETER
P.O. Box 7550 and transient LVPS modification.
170789 All Serials. Improved single sweep reset 5306A-3 Serials 1332AOO781 and below. Modification
Freeport Building
- operation. to ensure high mSHMty.
-4
r
P The Netherlands
For the U.S. and elsewhere, mail it to:
1810-1 181OA Serial weflx 1246A.18llA Serial
prefix 1245A and below. Marker dot intensity
modification.
~C~OOAIE)ICLASER HEAD, s b 0 6 LASER msplAv
~
5526A-3 All Serials. Laser safety regulation In USA.
5505A-1 Serials 1312 and below. solutlon for decade
noise problem.
1925A WORD GENERATOR
Hewlett-Packard Company 1925A-3A Serial prefix 1232A and below. Word 7MSA X-Y RECORDER
195 Page Mill Road count errors. 7035A-28 All Serials. Recommended replacement for
X-axis W O Motor.
Palo Alto, California 94306 3050A AUTO DATA ACQUISITION SYSTEM
3050A-1 All Serials. Troubleshooting. 71008ff101Bnl27Anl20A STRIP CHART
3 6 8 DIGITAL VOLTMETER
40 RECORDERS
KS-20826 (WESTERN ELECTRIC) IF-RF SWEEP 346059 All Serials. Troubleshooting reed relays in 71OO-7/7101-7/7127-7ffl28-7All Serials. Disposable
OSC (HP MODEL SSOSZ) the digital-to-analog converter. pen t p kit.
i
KS-20626-2 Serial prefix 1233A and below. Modi- 7203A BINARY GRAPHIC PLOllER
fication to improve frequency stability. 34702A YULllMETER
34702A-1/3474OA-1/34750A-l All Seriats. Modl- 7203A-1 All Serials. Recommended spare parts.
I
.I
13OC OSCILLOSCOPE fication to reduce AC zero offset. 72WA OPTICAL MARK READER
13OC-10 All Serials. Amplifier balance problems.
13012-1 All Serials. 03, Q4, 0203 and 0204
1 34703A DCV/DCAIfMETER 7260A-3 Serials prefix 1408A. Modificationto im-
replacement. 34703A-1 All Serials. Mnemonics glossary. prove external command timing.
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II ** I' :I SERVICE TIP / N E W SERVICE NOTES
II
ZJ
726OAl7861A OPnCAL MARK READERS 855884 Serial prefix 1334A and below. New front
7280A/72BlA4 All Serials. Read head lamp sub- p a d latch housing.
stitution. -A COMMUNICATIONSSWEEP OSCILLATOR
8008A PULSE QENERATOR 8605A-3 Serial prefix 1233A and below. Improved f e
r
8003A-3A Serial prefix 1233A and below. Line inter- quency stability.
ference in the gated mode.
88053 WESTERN ELECTRIC KS-20826 V-RF
855(iA SPECTRUM ANALYZER IF SECTION 8WOB SYNTHESKED SIGNAL GENERATOR
SWEEP OSCILLATOR
8556A-3 Serial prefix 1250A and below. Preferred 8660B-12A All Serials. Internal crystal osdllator
88052-2 Serial prefix 1233A and below. Improved
replacement for A5C5 (A5 Pre-attenuator/pre installation.
frequency stability.
ampliier Bd.) 868OB-16 Serials prefix 132OA and below. L.F. section
8566B SPECTRUM ANALYZER 8840- SKINAL QENERATOR transistor replacement.
66608-17 Serial prefix 1349A and below. Transformer
8
1
- All Serials. Bandwidthfilter board replace 864045-13. 8 W A Serial preRx 1244A and below. compatible with 4 voltage operation.
ment. 88408 Serial prefix 1243A and below, Installation of
85588-2 Serialprefix 1321Aandbelow. lmprovedfre- FM gah compensation circuit and potentiometer.
quency tuning pot. 864OA/B-14. Ail serials. Field installation procedure W6BACALCULATORCARDREADER
855t3B-3 Serial prefix 1334A and below. Prevention of for Option 001 (Variable Frequency Modulation 9869A-2 Serial00288 and below. Read headsensitivity
single sweep triggering by erase functlon. Oscillator). (when readers are equipped with option 003).
5300A MODULES MODIFICATION MINICALCULATOR
REPAIRS
The last issue of Bench Briefs an-
nounced the availability of minicalcula-
tor repairs at the HP Fullerton, Califor-
nia, office.These repairsare now hand-
led at
6315 Arizona Place
Los Angeles, Calm045
Telephone (213) 776-
80 for repair,
operating manual.
A modification is strongly recom- will cause the power line circuit
mended for several plug-on modules breaker to trip faster. This decreases
to the 5300A measurement system. the extent of damage caused by such
The modules affected are 5301A, operator error.
5302A, 53038, 5304A, 5306A, For more details, order Service Note
5307A, 531O and 5311A. This modifi-
A 530049-3 on the Service Note Order
cation increases the current carrying
capacity of the chassis ground circuit.
Form.
HP attempts to have products and a
7
There have been several instances warranty policy secondto none. Opera-
where operators have inadvertantly tor error such as connecting 115v (or
caused severe damage to the instru- 230v) to chassis is not covered by war-
ment while making measurements on ranty, of course.
power lines.
While making measurements on
They inadvertantly connected the
"hot" side of the power line to the chas-
power lines, exercise extreme cau- REPAIRING A 34550AB
tion.
sis terminal of input connector on the
plug-on. The resulting short circuit cur-
rent caused extensive damage to the
instrument. The recommended modifi-
cation increases the current carrying
A future article in Bench Briefs will dis-
cuss some of the techniques (such as
an isolation transformer) that can be
used to safely make measurements
Part number 1820-0426,which is used
on A13 for IC1 through IC5, can no
longer be obtained. The recommended
replacement for this IC in a 3450A or
e
capability of the chassis circuit which on power lines. 34508 is 1820-0707.
.
A
,
THE EDITORIAL STAFF WOULD LIKE YOUR OPINION
Would you take a few moments to indicate YOUR pre- 3. Would you like to see a detailed explanation of these cir-
ference for future Bench Briefs articles? This will be a cuits and techniques in future issues of Bench Briefs:
tremendous help in choosing what gets published.
Hewlett-Packard has extensive expertise in many
areas, and these experts are available to contribute
articles to Bench Briefs. What would YOU like to see?
Please fill in the survey and return to the correct ad-
dress shown on the reverse side.
0 0 0 0 0 Power supplies
0 0 0 0 0 Switching regulators
0 0 0 0 0 Tuned filters (active and passive)
1. Would you like to see Bench Briefs contain articles about 0 0 0 0 0 YIG oscillators
0 0 0 0 0 PIN modulators
these items:
0 0 0 0 0 Mixers
0 0 0 0 0 High frequency attenuators
0 0 0 0 0 Shaping and trigger circuits
0 0 0 0 0 V to F converters
0 0 0 0 0 D to A converters
0 0 0 00 A to D converters
0 0 0 0 0 Phase lock loops
0 0 0 0 0 new video tapes 0 0 0 0 0 Recorder servo systems
0 0 0 0 0 hand tools, extender boards, and other service 0 0 0 0 0 Strobed displays
aids available for repairing HP products 0 0 0 0 0 Character generators
0 0 0 0 0 cables, connectors and adaptors avail- 0 0 0 0 0 Heterodyning techniques
able for repairing HP products 0 0 0 0 0 S parameters
0 0 0 0 0 new HP products 0 0 0 0 0 Computer programming
0 0 0 0 0 cross references of HP part numbers to indus- 0 0 0 0 0 Would you be interested in buying a book con-
try numbers taining a detailed explanation of the above cir-
0 0 0 0 0 new service notes cuits and techniques?
0 0 0 0 0 new service manuals
0 0 0 0 0 Would you be interested in buying a book con-
taining articles about the items above?
4. Would you like to see a detailed explanation of how these
instruments function in future issues of Bench Briefs?
2. Would you like to see detailed explanation of these de-
vices in future issues of Bench Briefs:
0 0 0 0 0 Frequency synthesizers
0 0 0 0 0 Analog voltmeters
0 0 0 0 0 Vacuum Tubes 0 0 0 0 0 Digital voltmeters
OOOOOBWOs 0 0 0 0 0 Lasers
0 0 0 00 W S 0 0 0 00 Miniature calculators
0 0 0 0 0 Diodes 0 0 0 0 0 Frequency counters
0 0 0 0 0 Transistors 0 0 0 0 0 oscilloscopes
0 0 0 0 0 Analog IC's (operational amplifiers, diff-amps, 0 0 0 0 0 Pulse generators
etc. 0 0 0 0 0 Wave and distortion analyzers
0 0 0 0 0 Digital IC's (gates, flip-flops, counters, ROM's, 0 0 0 0 Spectrum analyzers
etc.) 0 0 0 0 0 Automated test systems
0 0 0 0 0 CMOS 0 0 0 0 Computer systems
0 0 0 0 0 Would you be interested in buying a book con- 0 0 0 0 0 Would you be interested in buying a book con-
taining an explanation of the above devices? taining an explanation of these instruments?
Thanks for your cooperation.
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P
0 Check here to receive a qualification form for
a free subscription to Bench Briefs.
L-----
Please check below the numbers of any desired service notes:
0 KS-206262 0 346OB-9 0 7203A-1 0 8660512A
0 130610 0 34702A-1134740A-11 0 7260A-3 0 8660816
0 13OCll 3475oA-1 0 7260Al7261A-4 0 86808-17
0 191A-3 0 34703A-1 0 80(KIA-3A 0 9869A-2
0 419A-3C 0 3475OA-2 0 8556A-3 0 AN36
0 47752 0 357OA-1 0 85588-1 0 AN57
0 1331A/cS 0 WOA-2 0 85588-2 0 AN158
0 133162 0 3570A-3 0 8558B-3 0 AN162
0 AN163-1
0 1401-2 0 357OA-4 0 85588-4
0.1703A- 4 0 53OoA-3 0 8605A-3
0 l703A-5 0 5308A-3 0 86052-2
D 170751 0 5526A-3 0 864OA/B-13
0 17078-3 0 5505A-1 0 8640NB-14
0 18104 0 7035A-28 0 8860A-16A
0 710&7/7101-7/ 0 8660A-18
712Wff128.7 0 WUJA-10
Reader Opinion Survey See page 7
__
. . . . . .- . - .. .- - - .... . .. . .
195 Page Mill Road
D . I ~ ditn rniifn.oip a,i?Iu:
Menlo Pa&, Ca.
Address Correction Requested
(VI r-ed. NO WI Or 5and1Briefs may be repoduoed wlmout the express consent Or the Editor. Ttw edtor may be telephoned at (415) 493-1212, extenrim 615.
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