Conar 251 Guide

v
.
^A,ssembling and Using your
CONAR
Solid'State Oscilloscope
Model 251
{
I
J
PRICE $2.00

Dan@
No matter what your experience has been with equipnrent, there's a new and even greater satisfaction
awaiting you in this CONAR product.
CONAR is a division of the National Radio Institute a pionee'r of more than 50 years in the Electronics
field. True. age alone is seldom a conrpliment. Yet there is no substitr"rte for the priceless ingredient of
experience. Irrtelligent design and engineering. clear-cut instructions written for the user. top-grade
components are your assurance you have made a wise choice a soltnd dollar itrvestntent.
The purpose of this book is to tell you how to get rnaxirnum value lrom this CONAR product. Please
read these instructions carefully and follow them faithfully. Then yoLt can rely on the dependable
service of CONAR quality.
We reserve the right to rnake changes in design or improvement when sttch changes or improvements
represent an equal or greater value to our customers.
There are four conditions under which you may have to write us about this CONAR product:
(l) It arrives damaged. First, examine the package to determine the method by which it was shipped
to yor.r. Then, follow the instructions or.r the form packed with this instrument advising proper pro-
cedures in case of damage.
(2) Parts are missing. If anything is missing. and you find no substitute or other instructions after
carefully examining the packirrg for small items, write us a letter explaining.
(3) A part has a defect. DEFECTIVE MATERIALS MUST BE RETURNED BEFORE A REPLACE -
MENT CAN BE MADE. TWO THINGS MUST BE WITH EVERY PACKAGE YOU RETURN TO US:
(l) Your name and address, (2) Your reason for returning it. You rnay enclose a letter in the package, if
you mark the package "first class letter enclosed." Such a package requires a stamp in addition to the
regular parcel post charge. Unless examination shows an obvious defect, write tlrst, and tell us why
you think the part is defective. Some other part may be causing the trouble.
(4) You lose or damage parts. Use the parts order form packed with this instrument. Be sure to
enclose your remittance as ordered parts are not sent C.O.D. or on accoLrnt.
CONAR INSTRUMENTS DIVISION OF NATIONAL RADIO INSTITUTE, WASHINGTON, D.C. 20016
WARRANTY
All CONAR products are guaranteed against factory defects
for ONE FULL YEAR. Any part or contpoltent that becomes
defective and such-defect is not the result of accidental damage,
improper Llse or wiring errors. will be replaced whe.n retumed
to CONAR.
COPYRIGHT 1980 BY NATIONAL RADIO INSTITUTE, WASHINGTON, D.C. 20016 Scanned by W2RIK

Circuit Board Assemblies Page 4
Contents
Introduction
Chassis Assembly
Final Assembly
Appendix
Page I
Page 26
Page 64
Page 83
Parts Lists
Circuit Boards Pages 4. 6,10,12,14, 18,20,21,and22
Chassis Pages 26, 30, 36, 38,42,44,46,50, and 54
Final Assembly Pages 66, 68,72,74,75,79.and82
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Introduetion
The Model 251 oscilloscope you are going to
build has many desirable features, including dc to 5
\lHz frequency response, automatic triggering, and
all solid-state circuitry. The Model 251 is a high-
performance, general-purpose oscilloscope, and is
ideally suited to many servicing or laboratory needs.
ln short, the Model 251 oscilloscope is an
instrument of which you can be very proud. Just
remember, the more you know about your scope,
the better you can use it and the more valuable a
tool it will be in your dailY work.
CAUTION
The cathode-ray tube supplied in this kit
is highly evacuated. Breaking the tube could
result in serious injury from flying glass. Do
not open the box in which the tube is packed
until you are told to do so. When handling the
tube, be careful not to strike it against
anything. Do not use excessive force when
installing it.
PREPARING FOR THE ASSEMBLY
Most of the parts in this kit are packed in
plastic bags. The bags have identifying labels on
them so that you can collect the bag or bags that
you will need for a particular assembly stage.
For example, the first bag that you will need
has a label that reads in part, 3A-41T. This bag is
divided into separate compartments. The parts in
each compartment are used in the assembly of the
power supply circuit board. Do not remove the
parts from the individual compartments until they
are called for in the instructions.
The parts list with each of the assembly stages
gives the part number, quantity, description, and
price of each of the parts. You should refer to the
parts lists if you ever have to order a replacement
part lor your instrument.
It is not necessary for you to check all of tire
parts of this kit at one time. Instead, gather and
check tire parts called for in each of the assembly
steps. If you find that a part is missing or damaged,
go ahead with your assembly and write to us for a
replacement.
The larger parts such as chassis pieces, trans-
formers, etc., are packed separately because of
their bulk and for extra protection. Examine each
part separately for damage. If any part was
damaged in shipment, write to us. A replacement
will be sent to you.
You may find an occasional substitution, such
as a 600 volt capacitor for a 400 volt capacitor, a
400 volt capacitor for a 200 volt capacitor, or a 5
percent resistor instead of a l0 percent resistor.
These changes are minor and will not affect the
operation of your instrument. If any other changes
are made, a special notice will be enclosed with your
training kit. Be sure to read all enclosures before
you start the assembly and your experiments.
ASSEMBLY HINTS
There is no satisfaction like that of building a
kit and having it work perfectly the first time you
try it. Here are some suggestions that will help you
reach that goal.
It's a good idea to read over the entire
assembly section before beginning actual construc-
tion. This way you get an overall picture of what is
to be done and how each stage of the assembly
relates to the others. When you are ready to begin
construction, read each step carefully and make
sure you clearly understand what must be done
before proceeding. After you perform each step,
check it off in the space ( ) provided and proceed
to the next step.
Follow the Instructions. Perform each step in
the exact order given. Don't try shortcuts such as
omitting steps or assembling the kit from the
schematic diagram. Our experience has shown that
even veteran kit builders make wiring errors when
they fail to follow directions. Tracking down and
correcting wiring errors in completed kits can be a
tedious and time-consuming process. By far, the
quickest shortcut is to follow the assembly instruc-
tions to the letter.
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Do a Good Soldering Job. Poor soldering is the
greatest single cause of problems in completed
units. A large part of the soldering in this kit will
be done on printed circuit boards. This makes it
easy to do a professional-looking construction job.
To do the soldering in this kit you will need a
small pencil-type soldering iron. A 25 to 50 watt
iron is satisfactory.
To mount components on the circuit boards,
unless you are told to do otherwise, first bend the
leads to fit the holes in the board using your
longnose pliers. Next, pass the leads through the
holes and press the component down until it rests
squarely on the surface of the board. You may
bend the leads on the other side of the board
slightly outward so the component stays put when
you turn the board over for soldering.
To solder the component leads to the foil pads,
apply the tip of your iron so that it touches both
the lead and the foil. At the same time, feed the
end of the solder to the lead and the foil until a
small mound of molten solder surrounds the lead
and covers the pad. When this happens, withdraw
the solder, then the iron.
After the solder has solidified, clip off the lead
close to the solder mound with your diagonal
cutters. When soldering components on the circuit
boards, watch out for solder bridges that cause
short circuits. Each time you solder a connection.
make sure that the solder mound covers only that
connection and does not run over to a nearby pad
or foil path.
When you connect wires and componeuts to
terminal lugs, controls, and other parts of the
chassis, be sure the mechanical connection of the
*ire or lead to the terminal lug is secure before
you solder. Do this by hooking the wire or lead
througJr or around the terminal lug, and then crimp
it with your longnose pliers.
Each chassis wiring step will include a notation
such as (NS), (Sl), (S2), or (S3). These notations
tell you whether to solder the connection made in
that step and, if so, the total number of wires to be
connected at that point. Each time you make a
soldeq connection, check to see that you have the
correct number of wires connected to the terminal
lug. The r"rotation (NS) indicates that a connection
should not yet be soldered because other wires will
be added. When you install the last wire, you will
solder the terminal. This will be indicated by the
letter S followed by a number, as explained
previously. This number tells you how many leads
are supposed to be connected to the terminal
before it is soldered. For example, if a step says,
"Connect a wire to lug 6 (S3)," there should be
three leads connected to this terminal before it is
soldered. In cases where a wire or colrlponent lead
passes through a terminal or lug and connects to
another terminal or lug, it counts as two leads, one
entering and one leaving the terminal or lug.
As we stated before, poor soldering is the
greatest single cause of problems in equipment
returned to us for repair. You can greatly reduce
the possibility of poorly soldered cotrnections in
your receiver if you clean the leads on resistors and
capacitors before installing them. Do this by
scraping the leads lightly witir a knife. or twisting
them between two pieces of fine satrdpaper.
You can further guard against poor soldering
by using a clean, hot iron at all tirnes. Be sure that
enough heat is applied to the solder connection to
avoid rosin joints. This is of the tttmost impor-
tance! Another important point to remember is to
avoid using too much solder. Use onll' enortgh to
lightly cover the leads and termir-ral )'ou are
soldering. Let any excess solder florv onto the tip
of your iron and wipe it off with a ra-e. Big blobs of
solder on terminals or circuit board pads are almost
certain to result in trouble.
Finally, use only the solder sr.rpplied in this kit.
If you buy more solder locally, make sltre the
container is marked "rosilt-core solder." DO NOT
USE ACID.CORE SOLDER OR SOLDER PASTE
FLUX. If you use either of these, you rvill ruin
yotrr oscilloscope. lile cannot sen,ice artl' eqttip-
nlent on tvlticlt acid-core solder or solder paste .flux
lrus beert usecl.
Use the Figures. Pictorial diagrams throughout
this manttal shorv the placement of parts and the
details of construction steps. In some cases a part
may fit into position iu more than one rvay. only
one of which is correct. Study the figures carefully
and make sure that you know exactly hotl' a part is
to be mounted before proceeding. In some cases
the illustrations may be sligJrtly distorted to show
certain details. In most instances the illustrations in
this manual show all parts in proper perspective-
You are now ready to begin an exciting
project. The oscilloscope you are going to buiid is a
valuable test instrutnent that will give you many
years of service.
For this reason, we urge you to take yolr time
and do careftil work. Some students get impatient
to finish the oscilloscope quickly rvitirout read::g
l
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all of the instrr,tctions. However, it is best to
erercise care duriug assembly and perform all of
the steps as tl-rey are presented. By doing this you
s'i1l be assured of obtaining a quality, well-built,
reli:b1e piece of equipment.
You will be assembling your oscilloscope in
several stages. Be sttre to check your work carefully
alter each stage to etrsure that all steps were
completed correctly. You will now begin building
your oscilloscope.
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Cireuit Board Assemblies
POWER SUPPLY MODULE ASSEMBLY
You will begin building your oscilloscope by
assembling the power supply module. The power
supply module contains most of the components
and circuitry for the three voltage sources (+5, +9,
and - 8 volts). It also contains the components and
circuitry for the final vertical deflection amplifier.
Gather the following parts:
Figure 1. Detail A.
SO LDE R
BOTH TABS
Figure l. Detail B.
4
Refer to Fig.l and begin the module assembly
by mounting and soldering the circuit board
receptacles. The details shown with Fig.l show
how the receptacles are installed.
We have supplied an extra receptacle in case
you lose or damage one. When you have completed
installing the receptacles, check your rvork and
proceed to the next step.
Remove the following parts from bag 3A-4lT:
Description
Power supply circuit board 2.75
Price
Each
Part
No. Quar,.
EC116 1
From bag 34-41T:
HA900 20'
so96 2r Rosinrcore solder
Circuit board receptacles
Description
I pF tantalum
360 p4 500 V silver mica
0.I trtF tantalum
330 ohms, 5%
t.5k,5%
4.7k,5%
3k, l0 watt
5.6k, 5 watt
.30ft
.05
hice
Eadr
Part
No. Quan.
CN261
CN29I
CN329
REI26
REl53
REzO2
R537
RSB9
,
I
I
,
I
1
,
2
INSERT FROM
COMPONENT SIDE
t
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Figure l. Installing the circuit board receptacles on the power supply module'
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Refer to Fig.2 and continue with the module
assembly. Be sure you correctly identify the
positive lead of each tantalum capacitor and ins.tall
it with the correct polarity on the circuit board.
Except when you are told to do otherwise, mount
all parts flush against the surface of the circuit
board. Solder all parts carefully and clip off the
excess lead lengths.
Use black hookup wire for all of the circuit
board jumpers. When bare wire is specified, stnp
off the required amount of insulation.
Part
No.
Remove
Qr"rr. hice
Egch
2.fi
r.00
2"50
.2t
.85
.IJ
t2'1.25
the following parts from
Description
bag 34-41T:
IG38 11
IGgB 1
IG99 I
sBlT 4
sB24 2
TS34 2
wR909 2'
7805 voltage regulator, 5 volts
7B[,t09 voltago regulator, 9 volts
79M08 voltage regulator, -B volts
1N4001 silicon diodes, l A 50 Pry
1N4007 silicon diodes, f A 1000 Pry
D40NI or MPSU1O transistors
Blackhookup wire
Figure 2. Detail A.
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Figure 2. Installing the resistors and capacitors on the power supply module.
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7
Refer to Fig.3 and continue with the module
assembly. Be zure you identify the cathode lead of
each diode and observe the correct polarity when
installing the diodes on your circuit board. Re.
member, the cathode is the marked or banded lead.
Also, when installing the transistors and voltage
regulators, be s-ure that the leads are positioned
properly as you insert them in the circuit board.
Figure 3, Detail A shows the lead identification for
the transistors used in this kit. For proper heat
dissipation, the transistors and regulators should be
mounted so that their bodies are about 3f 16" to*
lf 4" above the surface of the circuit board.
When you are asked to install a jumper, cut the
length specified from the black hookup wire. Then.
remove I /4" of insulation from each end of the wire.
Finally, install the jumper on the circuit board.
After you complete the power supply module,
carefully check the board to be sure that each con-
nection is secure, that there are no solder bridges
on the foil side, and that each component is installed
correctly. Set the completed circuit board aside.
79M08
tG99
78L09
tG98
7805
tG38
D4ONl-<>
M
7
g
MPSU 1O
I
2N5457
TS20
2N51 38
TS22
2N4124
TS43
Figure 3. Detail A.
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2 (l
rG98 (rC78L09)
SEE DETAI L A
Figure 3. Installing the remaining components on the power supply module.
o1
l'i';'; I I I
56
ll
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r
SWEEP/TRIGGER MODULE ASSEMBLY
You are now going to build the sweep/tngger
circuit board module. Follow the same general
procedures you used in building the power supply
rnodule,
Gather the following parts:
Part
No. Quan,
Part
NO. Quan Ilemiption hice
Eadr
2.75
8E145 1
REr59 I
88160 I
BE16r I
R8164 2
R8169 1
BEr?g 2
8E180 4
&8186 I'
R8189 I
RS5 I
Deseription
l?k,L0%
180ohm,5%
l.*.,5%
47Oo\tn,5%
lk,5%
47k,5%
L7k,S%
22k,ff/n
l2oahnrS%
620 ohmrl%
10k, I watt, l0%
ECtt4 I
From bag 4B4lT:
Sweep/Trig oirctit boerd
S'096 16 Circuit boerd rcceptaeles ,05
Refer to Fig.4 and begin the module assembly
by mounting and soldering the circuit board
receptaoles. After you have installed the recep-
tacleg, you will install the resistors.
Remove the following parts from bag 4B-4lT:
Part
No. Quan. Price
Eadr
.?A
' .24
.2/L
.211
.LtL
nElo
BE73
fE?4
REI02
8E126
Doscription
L00[,5%
rw5%
10k,5%
gr<" 5%
3?O olim,S%
1
2
I
1
IFigure 4. Detail A.
SOLDEB
BOTH TABS
t
Figure 4. Detail B.
+
.,\,
<\
N
.t5
.2,4
.?tL
.21
,24
.2/&
.2t
.24
,2/L
.2i
.m
FOIL
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1
CIRCUIT BOAFD
RECEPTACLES (10)
SEE DETAIL A AND B
().
2()
CIRCUIT BOARD
RECEPTACLES (6)
SEE DETAI L A AND B
Figure 4. Installing the circuit board receptacles on the sweep/trigger module.
11 Scanned by W2RIK

r
Re,fer to Fig.5 and continue with the module
assembly. After you have installed the resistors you
will install the capacitors, IC sockets, and tran-
sistors.
Remove the following parts
Part
No. Quan. Description
from bag 4B-4lT:
Part
No"
cN253
CNBOO
POl 21
PAt22
so84
soB6
TS20
TS22
TS34
T543
Quan.
a
I
t
I
2
1
2
I
I
4
Price
Each
.IJ
.50
.45
.45
.75
.lc
r.00
.40
.75
.4fr
CN34 1
cN102 I
cN104 r
0.001 pq disc
0.01 ptF, disc
0.1 pF, disc
hice
Each
.15
.40
.40
Description
2.2 trrF, tantalum
I0 /J4 tantalum
skr trim pot
INL trim pot
l4pin IC sockets
I6pin IC socket
2N5457 n+hannelJFETs
2N5138 transistor
D40Nl, D40V1, or MPSUIO transistor
2N4L24 transistors
rrcll,
Figure 5. Detail A
^)
,.,
1.'
hlt
\\
'V
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13 (
lOK, 1 WATT
BRN.BLK-ORN
SEE DETAIL A
rffilll"
DETAIL A
Figue 5. Iirstalling theredstors on the srv6ep/higger module.
l3 Scanned by W2RIK

Refer to Fig.6 and continue with the rnodule
assembly. You will now install the ICs in their
sockets.
Remove the following parts frorl bag 4B-4lT:
Part hice
No. Qr"r,. Description Flach
IG37 I 760 comparator IC 5.20
lG64 1 74132 quad 2-input NAND Schmitt
trigger TTL IC 1.25
lG97 I 74123 dual retriggerable one-shot IC .85
t4 Scanned by W2RIK

7
f
i
I
t
l
Or
,A.rr r(,t,l] o::r:.itr,,.@ - (o:
Dt] EOND
H.
n'
,o,i
.H
H
H
fi
(lr
grl
F.
li:r
',1:(f
l::..1I
s
tg . .T:IB
{::xI}
#?@ 0106
{:f$ fl'
Figure 6. lnstalling the remaining components on the sweep/trigger module.
n
a n..E ,n
IJJ
.J .nJ, t}r,,S
{
{
ilr
I
rl
r ()
so86 16-PtN tC
SOCKET 11 ()
TS34
MPSUlO OR D4ON1
z ()
TS20
2N 5457 12 ()
0.001 pF Dtsc
3 ()
PO121
5K TRIM POT 'r3 ()
so84 14-PtN tc
SOCKET
SEE DETAIL C
EC114=1OO
4 ()
so84 14-PtN tC
SOCKET
SEE DETAIL C14 ()
2.2 gF TANTA.LUM
OBSERVE POLARITY
1O I,IF TANTALUM
OBSERVE POLARITY 15 {)
PO122
trv rRru pol
6 ()
TS43
2N4124 16 ()
TS43
2N4124
17 ()
0.1 pF DrSC
8 ()
BARE 1 " JUMPER
19 ()
0.01 pF Drsc
10 ()
TS43
2N4124 2.2 I,lF TANTALUM
OBSERVE POLARITY
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Refer to Fig.7 and install the integrated cir-
cuits. Be sure to correctly locate pin I of each
integrated circuit.
When y-ou have finished assembling this
module, carefully check your board to be sure that
all of the eomponents are installed correctly and
that there are no solder bridges or poor solder
connsctions. Set the board aside and oontinue with
the next assembly stage. Figure 7. Detail A.
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