Heathkit IM-16 - Page 49

FUNCTIONAL
PARTS
LIST
R1
l-megohm
resistor in
probe.
Re-
duces the
loading of
the
circuit
under
test. Used
only
for
DC
voltage
mea-
surements.
AC
input
voltage
divider
on 1500 volt
range,
DC
return for rectifier
cir-
cuit on
all
AC
ranges.
Voltage
divider and
resistance mul-
tiplier resistors.
Dropping
resistor
in
AC
function, to
reduce rectified
AC
to
equivalent DC
voltage"
Series
resistor
in
gate
eircuit of
transistor
Q1.
With
Q2
and
Q3,
limits
voltage
at
gate
of
Q1.
Ohms
Adjust
control acrossE2.Ad-
justs
bias on
Q?
for full-scale
ohm-
meter
deflection.
Bias Adjust Control.
Sets
bias
range
for
Ql.
Zero
Adjust
Control.
Finer
adjust-
ment of
bias
on
Q1
to
set
meter at
left-end
zero,
Base
bias
voltage divider for
Q4.
Emitter
resistor
of
constant current
source
Q4.
Sets
current
through
Q4
and
Q1"
Emitter
load
resistors for output
transistors
Q5
and
Q6.
AC
Calibration control.
DC
Calibration control.
Base
bias voltage
divider for
Q6
Series
current
limiter
for
neon
pilot
lamp.
Series dropping
resistor for
line
operation"
Sets
current through
D5"
Series
dropping
resistor
for battery
operation.
Emitter
resistor
for
Q?,
With
R17
-
sets
current
of ohms
supply
E2
through
R14"
AC
input
coupling
capacitor" Blocks
DC.
Charging
capacitor. Charges
topos-
itive
peaks
of
AC
input
voltage.
Forms
low-pass
filter with
R16.
Re-
duces
hum at
gate
of
Q1,
AC power
supply
charging capacitor.
AC
bypass for
bias network.
Silicon
diode.
Rectifies AC
input
voltage.
Silicon
diodes
in series
with
D1
for
500
and 1500
volt
AC
ranges,
Silicon diode
power
supply rectifier.
6.8 volt
zener
diode.
Regulates
B+
supply
voltage.
Field
effect transistor
(FET),
Used
as a
source follower to
providehigh
impedance input and
low
impedance
output
to transistor
Q5.
2N3393 transistors
connected to act
as
9-volt
zener
diodes. Protects
Ql
and
output
circuit
from
severe
overload.
Constant
current source
for
Ql.
Used as a
source
resistor.
Output transistors.
Provide
voltage
and
current
to
operate
meter.
Constant
current
source for
ohm-
meter
circuit.
R32
R33
D2, D3
Q2,
Q3
Q4
Q5, Q6
Q7
R2,
R3
R4-R14
R15
Rl6
Rl7
R18, R20
R]"9
RzL,
PJ22
R23
R24, P"27
P"25
R26
R28,
R29
R30
R31
C3
C1
C2
c4
C5
D1
D4
D5
Q1