Heathkit IM 2420 Manual

Page 42

Page 40

Refer to Pictorial 4-4 [Illustration Booklet, Page 7) for
the following steps.

QQL Solder the remaining lugs of switches SW2 and
SW3 to the foil.

Refer to inset drawing #2 on Pictorial 4-4 and
solder the free end of the solder lug on switch
shaft SW2 to the foil on the printed side of the
main circuit board.

[76: Cut each lead of the .l 5 p.17 polycarbonate
capacitor to 1/2.
IMPORTANT: To ensure that your completed fre-
quency counter operates properly over its entire fre-
quency range. it is very important that you keep the
length of each lead and wire in the following steps as
short as possible. After you install each component or
wire, cut off any excess length on both ends.
9Q Cl: Connect the .15 F polycarbonate capacitor
from the main circuit board holeAB (8-1) to the
center lug of BNC connector )1 (SJ). Wrap the
end of the lead around the lug as shown in inset
drawing #1 before you solder the connection.

(4, Cut each lead of the 15 fl (brn-grn-blk) resistor

to 3/4".
99

Ran/FBI: Slide the ferrite head onto one lead of
the 15 a resistor. Connect this lead to main
circuit board holeAD (3-1). Wrap the end of the
other resistor lead around the center lug of BNC
connector )2 before you solder the connection.

Connect the following lengths of bare wire from the
main circuit board to the front panel assembly as
follows:

Z
(x.

3/4 wire from hole AC (3-1) to the solder lug at
BNC connector )1 (8-1).

3/4 wire from hole AE (8-1) to the solder lug at
BNC connector )2 (8-1).

3

Connect a 3/4 bare wire from switch SW1 his 1
(NS) to lug 2 (8-1).

Locate the 1-3/4 gray wire that you set aside

earlier. Then remove 114' of insulation from
each end and prepare the ends.

(lucnlfl

Heathkit'

(fl, Connect the prepared 1-3/4" gray wire, from
control R9 lug 2 [8-1) to SW1 lug 4 (54).

Cut a 9" length of 8-wire cable.

At one end of this cable. separate the wires
between the red and orange leads. Also, sepa-
rate them between the blue and violet wires.

Completely separate the gray and violet 2-wire
cable from the other wires. Set this 2-wire cable
aside temporarily.

In the same manner. separate the blue. green,
yellow, and orange 4-wire cable from the other
wires. Set this 4-wire cable aside and discard
the red and brown wires.

Refer to Detail 44A, Part A and prepare the
ends of the 2-wire cable as shown.

Uzuli
1M"

VIOL
(NW

9"
"III 1"
2- ma: CABLE

YEL
GRN
BLUo

wilt-[0 1/2" rm 5"61118 fill"

4- 1/2" E
1" 'IIT I 12"
00 Im" emu: CABLE I

RED
Okcfi

Vilfi
SHORT 3 WIRE CABLE

9..
Plll I
lONG 3-WIRE CABLE

_. 1/2..
3/16"»
RED l-
ORG
VEL

We! -
c:-

.I +lI4"

Page 48

Page

LARGEG
P AROUND SPR IN
CRWllARE AFTER CONNECTOR

SOLDER COOLS DO NOT ALLOW

SOLDER T0 FLOW
IN THIS AREA

CRIMP
AND
SOLDER

SMALL (>9
m: .
6-HOLE
couuzcmn
SHELL
\
Lu-
BLU am am

RED RED-YEL
Detail 4-5L

[Pd Locate the power transformer. the 6-hole con-

nector shell and six large spring connectors.
(sf) At the free end of the two red. two blue.
blue/yellow, and red/yellow transformer wires.
cut the exposedbared end of each wire to 1/8" as
shown in Detail 4-5L.

Refer to Detail 4-5L and install a large spring
connector on each of these six transformer
wires.

2C)

NOTE: The 6-hole connector shell may be marked
with small numbers. Ignore these numbers in the next
step.

Refer to Detail 4-51. and push the spring connec-
tors on these six transformer wires into the
6-hole connector shell as shown. Be sure the
connector shell is positioned with its slots up
Push on each wire until the locking tab on the
spring connector snaps into place.

each of the two power transformer feet.

Refer to Detail 4-5N and mount the transformer
bracket to the chassis at the location shown. Use
6-32 x 3/8 black phillips head hardware at
each mounting hole. DO NOT tighten the

fl Remove any excess varnish from the bottom of

Heathkit'

@342 NUT
\égs LOCKWASHER

\
llD FLAT WAS|HER

TRANSFORMER
ERACKET

6-32 x 3/!"
BLACK PHILLIPS
HEAD SCREW

POWER
TRANSFORMER

REMOVE EXCESS
VARNISH

E 8-32 r 3/3
: BLACK
SCREW

Detail 4-5N

({K T1: Again refer to Detail 4-5N and mount the
power transformer at location T1 on the chassis
with 8-32 x 3/8" black hardware. Position the
transformer as shown in the Pictorial.

Tighten all hardware to secure the transformer
bracket to the chassis.

he

Refer to Pictorial 4-6 (Illustration Booklet, Page 9) for
the following steps.

yii
Ps1

Cut a 3-1/2" length of the 4-wire cable you set
aside earlier. Discard the longer length of this
cable.

Refer to Detail 443A. Part A and prepare the
ends of the 4-wire cable as shown.

Refer to Detail 4-6A. Part B and install a small
spring connector on each wire at end A of this
cable.

hardware yet.
0 34 3/. 1 (menu) 2 3
l"'I'l"I""I I I J l I l J l I
l l ' I l I I I I r I ' I
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Page 56

Page54

IC INSTALLATION AND TESTS

If it has not already been done, set the switches
as shown in Pictorial 5-2 (Illustration Booklet,
Page 11).

POWER - STBY

TRIGGER - PRESET

MODE - FREQ A.

RANGE - aS-Ml-lz (fully counterclockwise)
10 MHz TIME BASE - INT

Refer to Pictorial 5-2 for the following steps.
NOTES:

1. Make sure you do not short any adjacent termi-
nals or fails when you make tests or voltage
measurements. If a probe or test lead slips, for
example. and shorts together two adjacent con-
nections, it is very likely to damage one or more
of the transistors. diodes, or 10's.

2. Be especially careful when you test any circuit
that contains an IC or a nansistor. Although
these components have an almost unlimited life
when used properly. they are much more vul-
nerable to damage from excess voltage and cur-
rent than many other parts.

3. Do not remove any components while the unit is
turned on.

4. Use a voltmeter with a high input impedance
when you measure voltages.

( 1 Connect the voltmeter's common lead to the
chassis.

( ) Set your voltmeter to measure +1.5 volts DC.

CAUTION: Integrated Circuits (10's) are complex
electronic devices that perform many complicated
functions in thevcircuit. These devices can be dam-
aged during installation. Read all of the following
information before you install them.

The pins on the [Ca are bent out at an angle. so they do
not line up with the holes in the IC socket. Do NOI try
to install an 1C without first bending the pins as de
scribed below. To do so may damage the IC pins or the
socket. causing intermittent contact.

Heathkit'

IC LEADS

Before you install an IC, lay it down on its side as
shown below and very carefully roll it toward the pins
to bend the lower pins into line. Then turn the [C over
and bend the pins on the other side in the same man-
ner.

Make sure that the pin 1 end of the 1C is positioned
over the index mark on the circuit board. Refer to the
inset drawing on Pictorial 5-2. Also, make sure that all
of the pins are started into the socket. Then press the
IC firmly into the socket. NOTE: An 10 pin can be-
come bent under the IC and it will appear as though it
is correctly installed in the socket.

NOTE: An IC lifter has been furnished so you can
remove a dual-in-line [C from its socket if this should
be necessary.

Push the shorter and of the lifter in between the IC and
the socket and rock the longer portion back and forth.
Be very careful. as the IC pins are very easily bent.

Page 83

Heathkit

The time-base signal is generated by the oscillator at
box C. The signal is sent to box E, where it is accepted
because the control voltage at U83 pin 10 is high (the
control voltage comes through inverting amp UGA).
The time-base signal frequency is then divided by the
divider chain.

Some frequencies go through box F. which sends one
frequency on to box H; box H rejects this input be-
cause the control voltage to U7A pin 2 is low. The four
lowem frequencies from box E are sent to box G. Only
one otthess isallowed to go on tobox K. Range switch
ssz provides a high control voltage to one of the
AND gates (1117 A, B. C, orD). allowing the time-base
frequency for that gate to peas.

Box K accepts the time-base signal because the con-
trol voltage at UBE pin 4 is high (the control voltage
comes through inverting amp 061'). The output of box
K goes to box M.

Box M divides the signal from box K by two. produc-
ing a high control voltage that is equal to one count
period, followed by an equally long low control volt-
age (except as modified by the input from the store-
reset process circuits-mes "Store-Reset Operation,"
Page 79). The box M output goes to box L as a control
voltage and to box N to initiate the store-reset process.

FREQUENCY B MODE

Refer to the Frequency B Block Diagram (Illustration
Booklet. Page 14) as you read the following.

in the frequency count modes. the frequency is pro-
cessed through the circuih'y to the gate in box L. The
box C. E. G. K.and M series opens the gate at bofoor
either 10 msec, 100 mass, 1 sec, or 10 sec. While the
gate is open. the frequency is counted at box R. The
decimal point is adjusted to give the count in terms of
kHz or MHz.

The frequency-to-be-counted signal comes into box B
through jack 12 and is amplitude limited, amplified.
divided by ten. and converted to 111.. voltage levels.
The signal then goes from box B to box D. It is ac-
cepted at box D because the control voltage at 04D pin
12 is high.

Page 31

From this point on. the process is exactly the same as
in the Frequency A Mode.

Box D performs the functions of input selection and
changing the signal-to-be-counted into a series of
very narrow pulses.

The signal from box D goes to box H where it is
accepted because the control voltage at U7D pin 13 is
high (this control voltage comes through inverting
amlpoilsh). The signal passes through box H and goes
to L.

Box L treats the signal from box H as signal-to-be-
counted. and treats the input from box M as a control
signal. When the signal from box M is high (one count
period], the signal-to-be-counted is accepted by box
L. When the signs] is low (between count periods; due
to the store and reset cycles], box L rejects the signal-
to-becounted.

Box 1. sends the signal-to-be-counted to box R where
it is counted. and then displayed at the end of each
count sequence.

The time-base signal is generated by the oscillator at
box C. The signal is sent to box E. where it is accepted
because the control voltage at U83 pin 10 is high (the
control voltage comes through inverting amp U63).
The time-base signal frequency is then divided by the
divider chain.

Some frequencies go through box P. which sends one
frequency on to box H; box H rejects this input be
cause the control voltage to 07A pin 2 is low. The four
lowest frequencies from box E are sent to box G. Only
one oftheseis allowed to go cntobox K. Range switch
SWZA provides a high control voltage to one of the
AND gates (U17A, B, C. or D). allowing the time-base
frequency for that gate to pass.

Box K accepts the time-base signal because the con-
trol voltage at UBE pin 4 is high (the control voltage
comes through inverting amp USP]. The output of box
K goes to box M.

Box M divides the signal from box K by two, produc-
ing a high control voltage that is equal to one count
period, followed by an equally long control voltage
(except as modified by the input from the store-reset
process circuits-see Store-Reset Operation." Page
79). The box M output goes to box L as a control
voltage and to box N to initiate the store-reset process.