Elenco Electronics FM-88K Assembly And Instruction Manual

AUTO-SCAN FM RADIO KIT
MODEL FM-88K
ELENCO®
150 Carpenter Avenue
Wheeling, IL 60090
(847) 541-3800
Website: www.elenco.com
e-mail: [email protected]
To see our complete line of Educational Products
go to WWW.ELENCO.COM
Assembly and Instruction Manual
ELENCO
®
Copyright © 2011 by ELENCO® All rights reserved.
No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
753050
PARTS LIST
GLOSSARY (Continued)
If you are a student, and any parts are missing or damaged, please see instructor or bookstore. If you purchased this
kit from a distributor, catalog, etc., please contact ELENCO® (address/phone/e-mail is at the back of this manual) for
additional assistance, if needed. DO NOT contact your place of purchase as they will not be able to help you.
RF
Radio Frequency.
Sensitivity
The ability of a receiver to pick
up low-amplitude signals.
Speaker
An electronic device that turn
electric impulses into sound.
Surface-mount
Technology
RESISTORS
Symbol
R5
R1
R3
R4
R2
R6/S3
Value
Color Code
10Ω 5% 1/4W
brown-black-black-gold
680Ω 5% 1/4W
blue-gray-brown-gold
5.6kΩ 5% 1/4W
green-blue-red-gold
10kΩ 5% 1/4W
brown-black-orange-gold
18kΩ 5% 1/4W
brown-gray-orange-gold
Potentiometer 50kΩ & switch w/ nut & washer
Part #
121000
136800
145600
151000
151800
192522
CAPACITORS
Qty.
r1
r1
r1
r1
r1
r1
r1
r1
r2
r1
r1
r6
r2
r1
r1
r2
Symbol
C6
C7
C10
C5
C8
C4
C13
C23
C11, C12
C15
C19
C3, C9, C14, C16, C17, C*
C21, C22
C20
C1
C2, C18
Value
33pF
82pF
180pF
220pF
330pF
470pF
680pF
1500pF
3300pF
0.033μF
0.047μF
0.1μF
10μF
22μF
100μF
220μF
Description
Discap (33)
Discap (82)
Discap (181 or 180)
Discap (221 or 220)
Discap (331 or 330)
Discap (471 or 470)
Discap (681 or 680)
Discap (152)
Discap (332)
Discap (333)
Discap (473)
Discap (104)
Electrolytic radial
Electrolytic radial
Electrolytic radial
Electrolytic radial
Part #
213317
218210
221810
222210
223317
224717
226880
231516
233310
243318
244780
251010
271044
272244
281044
282244
COILS
Qty.
r1
r1
Symbol
L2
L1
Value
Qty.
r1
r1
r1
r1
r1
Symbol
D1
D2
D3
U2
U1
Value
BB909/BB910
1N4001
Description
Coil 4-turn
Coil 6-turn
Part #
430150
430160
SEMICONDUCTORS
LM-386 or identical
TDA7088T or identical
Description
Varactor
Semiconductor silicon diode
Red LED 3mm
Low voltage audio power amplifier
FM receiver SM installed on PC board
Part #
310909
314001
350003
330386
MISCELLANEOUS
Qty.
r1
r1
r2
r1
r1
r1
r1
r1
Description
Antenna FM
PC board w/ installed U1 (TDA7088T)
Push button switch 12mm
Battery holder
Speaker 8Ω
Cap push button switch yellow
Cap push button switch red
Knob pot / switch
Qty.
r1
r2
r1
r1
r1
r 3”
r1
Part #
484005
517038
540005
590096
590102
622001
622007
622050
-1-
Description
Screw M1.8 x 7.5mm
Antenna screw M2 x 5mm
Nut M1.8
Socket IC 8-pin
Speaker pad
Wire 22 ga. solid
Solder Lead-free
Part #
641100
643148
644210
664008
780128
834012
9LF99
Trimmer
A semiconductor component
that can be used to amplify
signals, or as electronic
switches.
Varactor
A method of using special
components that are soldered
to the PC board’s surface.
A diode optimized to vary its
internal capacitance with a
change in its reverse bias
voltage.
Voltage
Electrical potential difference
measured in volts.
An
adjustable
fine-tuning
resistor, capacitor, or inductor of
small values.
Voltage Regulator A circuit that holds the DC
voltage.
QUIZ
INSTRUCTIONS: Complete the following examination, check your answers carefully.
6. The capacitance of the varactor is determined by . . .
r A) the voltage level.
r B) the amount of current in the circuit.
r C) the signal strength of the RF carrier.
r D) the amount of resistance in the circuit.
1. The number of cycles produced per second by a source
of sound is called the . . .
r A) amplitude.
r B) vibration.
r C) sound wave.
r D) frequency.
7. The ability to select a specific band of frequencies,
while rejecting others, is called . . .
r A) selectivity.
r B) sensitivity.
r C) demodulation.
r D) none of the above.
2. The frequency of the modulating signal determines the
...
r A) number of times the frequency of the carrier
changes per second.
r B) maximum deviation of the FM carrier.
r C) maximum frequency swing of the FM carrier.
r D) amount of amplitude change of the FM
carrier.
8. The process of mixing two signals to produce a third
signal is called . . .
r A) filtering.
r B) detecting.
r C) rectification.
r D) heterodyning.
3. The FM broadcast band is . . .
r A) 550 – 1,600kHz.
r B) 10.7MHz.
r C) 88 – 108MHz.
r D) 98.7 – 118.7MHz.
9. The circuit designed to supply substantial power output
into low impedance load is called . . .
r A) power supply.
r B) pre-amplifier.
r C) power amplifier.
r D) detector.
4. The AFC circuit is used to . . .
r A) automatically hold the local oscillator on
frequency.
r B) maintain constant gain in the receiver to
prevent such things as fading.
r C) prevent amplitude variations of the FM
carrier.
r D) automatically control the audio frequencies
in the receiver.
5. The device most often used for changing the local
oscillator frequency with the AFC voltage is a . . .
r A) feedthrough capacitor.
r B) variable inductor.
r C) varactor.
r D) trimmer capacitor.
10. The gain of the LM-386 amplifier can be set in range
from . . .
r A) 1 to 20.
r B) 20 to 200.
r C) 0 to 200.
r D) 50 to 100.
Answers: 1. D, 2. A, 3. C, 4. A, 5. C, 6. A, 7. C, 8. D, 9. C, 10. B
Qty.
r1
r1
r1
r1
r1
r1
Transistor
-14-
PARTS IDENTIFICATION
TROUBLESHOOTING
Contact ELENCO if you have any problems. DO NOT contact your place of purchase as they will not be able
to help you.
®
r d) Have any solder bridges formed? A solder
bridge may occur if you accidentally touch an
adjacent foil by using too much solder or by
dragging the soldering iron across adjacent
foils. Break the bridge with your soldering
iron.
1. One of the most frequently occurring problems is
poor solder connections.
r a) Tug slightly on all parts to make sure that
they are indeed soldered.
r b) All solder connections should be shiny.
Resolder any that are not.
Resistor
LM-386
6-turn
3. Make sure that all of the parts are placed in their
correct positions. Check if the IC, diode and lytic
orientations are correct.
LED
Electrolytic
Discap
radial
Diode
-OR-
AGC
Automatic Gain Control.
AF
Audio Frequency
AM
Amplitude Modulation
Amplifier
Converts input signal to output.
Anode
The positive terminal of a diode.
Detector Circuit
Diode
Receiver circuit that recovers
the modulated portion of the
signal impressed on the RF
carrier wave.
Frequency Modulation.
Any device that either radiates
a signal or pulls in a signal.
Frequency
Wave or pulse repetition rate.
Baffle
Used to ensure positive airflow.
Gain
Signal multiplication.
Bandwidth
The amount of frequency
spectrum, in hertz, utilized by a
filter or channel.
IC
Integrated Circuit.
LED
Light Emitting Diode. A
semiconductor device that
emits light when voltage and
current are passed through it.
PC Board
Printed Circuit Board.
Potentiometer
Three-terminal variable resistor,
volume control.
Bypass Capacitor A capacitor used to shunt AC
around a component.
An electronic component that
has ability to store a charge and
block DC current.
The negative terminal of a
diode.
Coil
A component with inductive
reactance.
Current
Transport
of
electrons
throughout a conductor and
measured in amps.
Power Supply
Resistor
-13-
50kΩ Potentiometer
and switch
4-turn
FM antenna
Speaker
Battery holder
Push button switch
Cap push button
switch
Knob (pot / switch)
Speaker pad
An electronic circuit that
produces the necessary power
for another circuit.
An electronic component that
obstructs (resists) the flow of
electricity.
Varactor
MISCELLANEOUS
An electronic component that
changes alternating current to
direct current.
FM
Cathode
SEMICONDUCTORS
COILS
IC Socket
GLOSSARY
Capacitor
CAPACITORS
2. Use a fresh 9V battery.
r c) Solder should flow into a smooth puddle
rather than a round ball. Resolder any
connection that has formed into a ball.
Antenna
RESISTORS
PC board
Screw
M1.8 x 7.5mm
Screw
M2 x 5mm
Nut M1.8
-2-
TESTING - SECTION 2
You Will Need:
• 9V Battery
• 25 or 30 watt Soldering Iron
• Small Phillips and Slotted Screwdrivers
• Long Nose Plier
• Side Cutters
Voltage reference chart for U1 TDA 7088T (turn radio
on and press reset).
Test
IDENTIFYING RESISTOR VALUES
Verify that FM signals are present in your location by
listening to another FM radio placed near the FM-88K.
Use the following information as a guide in properly identifying the value of resistors.
BAND 1
1st Digit
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Digit
0
1
2
3
4
5
6
7
8
9
BAND 2
2nd Digit
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Digit
0
1
2
3
4
5
6
7
8
9
Multiplier
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Silver
Gold
Color
Silver
Gold
Brown
Red
Orange
Green
Blue
Violet
Tolerance
±10%
±5%
±1%
±2%
±3%
±0.5%
±0.25%
±0.1%
2. Bend the antenna to vertical position and
adjust for maximum length.
BANDS
2
1
Multiplier
Tolerance
Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or μF (microfarads).
Most capacitors will have their actual value printed on them. Some capacitors may have their value printed in
the following manner. The maximum operating voltage may also be printed on the capacitor.
Warning:
If the capacitor is
connected
with
incorrect polarity, it
may heat up and
either leak, or cause
the capacitor to
explode.
Multiplier
For the No.
0
1
2
3
Multiply By
1
10
100
1k
Second Digit
First Digit
4
5
8
10k 100k .01
100V
Means
Pico
nano
micro
milli
unit
kilo
mega
0.1
Tolerance*
Maximum Working Voltage
The value is 10 x 1,000 =
10,000pF or .01μF 100V
Polarity
Marking
* The letter M indicates a tolerance of +20%
The letter K indicates a tolerance of +10%
The letter J indicates a tolerance of +5%
Note: The letter “R”
may be used at times
to signify a decimal
point; as in 3R3 = 3.3
METRIC UNITS AND CONVERSIONS
Abbreviation
p
n
μ
m
–
k
M
9
Multiplier
103K
Multiply Unit By
.000000000001
.000000001
.000001
.001
1
1,000
1,000,000
Or
10-12
10-9
10-6
10-3
100
103
106
-3-
3. Turn ON power switch (rotate clockwise until a
“click” is heard). RED LED should light. Turn
the VOLUME CONTROL potentiometer to
middle position (comfortable level).
4. Press and release “RESET” ( R ) button.
IDENTIFYING CAPACITOR VALUES
Electrolytic capacitors have a positive
and a negative electrode. The negative
lead is indicated on the packaging by
a stripe with minus signs and possibly
arrowheads.
Figure L
1. Install fresh 9V battery into holder.
Resistance
Tolerance
Multiplier
1
10
100
1,000
10,000
100,000
1,000,000
0.01
0.1
If the radio is receiving station frequencies higher than
90MHz after pressing the “RESET” button, you will
need to adjust coil L2 to a higher value (by making the
gap between the coils smaller as shown in Figure L).
Carefully press the coils of L2 together.
Press and release the “SCAN” ( S ) button once or
a couple of times; a station should be heard. Press
and release “SCAN” button again; the radio should be
automatically searching for other broadcast station.
When you press the “SCAN” button in several times,
there should be other broadcast stations coming
before the HIGH-END frequency (FM106-108MHz).
If test fails;
If the radio is receiving station frequencies smaller than
87MHz after pressing the “RESET” button (to receive
regular FM stations you need to press the “SCAN”
button several times), then you will need to adjust the
L2 coil to a smaller value (carefully slide a small
screwdriver between coils to get the spacing shown in
Figure M).
Make sure that all of the parts are placed in
their correct position. Check if the orientation
of D1 is correct.
Short pins 2 and 14 of U1 several times using
a wire. If you don’t hear tapping from the
speaker, check U1, capacitors C22 and C23,
resistor R2, and potentiometer R6.
Pin #
Voltage
Pin #
Voltage
1
2
3
4
5
6
7
8
2.4
1.3
2.2
2.6
2.6
2.0
1.9
1.2
9
10
11
12
13
14
15
16
1.9
1.9
0.9
0.9
1.8
0
1.7
2.1
If sound is not clear;
Install capacitor C* onto the copper side of the
PC board as shown in Figure N.
If you need more gain (up to 200), install
capacitor C21 (10μF) as shown in Figure D.
Figure M
1. 1,000 pico units
= 1 nano unit
2. 1,000 nano units
= 1 micro unit
Alignment
3. 1,000 micro units
= 1 milli unit
4. 1,000 milli units
= 1 unit
5. 1,000 units
= 1 kilo unit
6. 1,000 kilo units
= 1 mega unit
The first time “SCAN” button is pressed, the radio
should start at the bottom end of the FM band (88-90
MHz). You may need to press the SCAN button a
couple of times. If it doesn’t tune to the low end, you
will need to adjust the coil.
-12-
Figure N
DESCRIPTION AND FEATURES
SECTION 2
ASSEMBLE COMPONENTS TO THE PC BOARD
Place a check mark
in the box provided next to each step to indicate that the step is completed.
C5 - 220pF Discap (221 or 220)
S1 - Push button switch
S1 - Cap yellow
(see Figure J)
R4 - 10kΩ 5% 1/4W Res.
(brown-black-orange-gold)
The ELENCO® FM-88K Kit is a monophonic, two-IC, FM
(frequency modulation) receiver designed to receive FM
signals in the frequency range (88-108MHz). It uses
electronic auto-scan to search for FM stations. This scan
system is done with two button switches - one switch scans
up, the other resets to the start of the tuning position.
The unique design of this radio kit allows you to place the
parts over the corresponding symbols in the schematic
drawing on the surface of the printed circuit board. This
technique maximizes the learning process, while keeping
the chance of assembly error at a minimum.
To simplify troubleshooting the FM radio, it is constructed
in two sections (Audio and RF). There are two IC’s, one
for the audio section, the other for the RF. The RF IC is
surface mounted (SM-IC), pre-installed on the high quality
printed circuit board.
•
•
•
•
C7 - 82pF Discap (82)
S2 - Push button switch
S2 - Cap red
(see Figure J)
C8 - 330pF Discap (331 or 330)
C14 - 0.1μF Discap (104)
• Electronic auto-scan FM RADIO FM-88K is a receiver
for searching FM stations
• Operated by two push button switches
• Frequency range: (88 – 108) MHz
• High sensitivity
C11 - 3300pF Discap (332)
R3 - 5.6kΩ 5% 1/4W Res.
(green-blue-red-gold)
INTRODUCTION
C22 - 10μF Electrolytic
(see Figure D)
The FM (Frequency Modulation) band covers 88 –
108 MHz. There are signals from many radio
transmitters in the band inducing signal voltages in
C6 - 33pF Discap (33)
L1 - Coil 6-turn (see Figure K)
C9 - 0.1μF Discap (104)
Volume control of 8Ω speaker
Telescopic antenna
LED power ON indicator
Power source 9V battery with ON/OFF power switch
the area. Below is a block diagram of a basic
SUPERHETERODYNE FM radio:
C4 - 470pF Discap (471 or 470)
C16 - 0.1μF Discap (104)
Speaker
C15 - 0.033μF Discap (333)
RF
AMPLIFIER
L2 - Coil, 4-turn
(see Figure I)
MIXER
IF
AMPLIFIER
OSCILLATOR
AFC
DETECTOR
AUDIO
AMPLIFIER
r Install FM antenna
C12 - 3300pF Discap (332)
Mount the antenna to the PC board
using two M2 x 5mm screws as
shown.
C10 - 180pF Discap
(181 or 180)
C23 - 1500pF Discap (152)
FM antenna
Note: Capacitors C21 and C* are not used.
Figure I
Figure J
Figure K
Using a spacer, create three
1/16” gaps in the 4-turn coil as
shown. Mount the coil to the
PC board as shown. Solder
and cut off excess leads.
Mount the push button switch flush to
the PC board and solder into place.
Attach the plastic button cap to the
switch by snapping it into place.
Mount the 6-turn coil to the PC
board as shown. Solder and cut
off excess leads.
Button cap
1/16” gap
Push button
switch
Legend side of PC board
M2 x 5mm Screws
-11-
FM RF AMPLIFIER, MIXER, OSCILLATOR
FM DETECTOR
The RF amplifier selects and amplifies a desired
station from many. It is adjustable so that the
selection frequency can be altered, also known as
tuning. The selected frequency and the output of an
Oscillator are applied to the mixer, forming a
frequency changer circuit. The RF amplifier and the
oscillator are the only two resonant circuits that
change when the radio is tuned for different stations.
Since a radio station may exist 10.7MHz above the
oscillator frequency, it is important that the RF stage
rejects this station and selects only the station
10.7MHz below the oscillator frequency.
The amplified IF signal is fed to the detector. This
circuit recovers the audio signal and discards the IF
carrier. Some of the audio is fed back to the oscillator
as an Automatic Frequency Control (AFC) voltage.
This ensures that the oscillator frequency is stable in
spite of temperature, voltage, and other effects
changes. If this occurs, the center frequency of
10.7MHz will not be maintained. AFC is used to
maintain the 10.7MHz center frequency. When the
local oscillator drifts, the radio detector will produce
a DC (direct current) “correction” voltage. This signal
is fed to a filter network that removes the audio so
that pure DC voltage is produced and changes the
frequency of oscillation of the local oscillator.
The frequency of the undesired station 10.7MHz
above the oscillator is called the Image Frequency.
Since the FM receiver has an RF amplifier, the image
frequency is reduced significantly. The output from
the mixer is the Intermediate Frequency (IF), a fixed
frequency of 10.7MHz. The IF signal is fed into the
IF amplifier. The advantage of the IF amplifier is that
its frequency and bandwidth are fixed, no matter
what the frequency of the signals. The IF amplifier
increases the amplitude, while also providing
selectivity. Selectivity is the ability to “pick out” one
station while rejecting all others.
AUDIO AMPLIFIER
The audio amplifier increases the audio power to a
level sufficient to drive an 8Ω speaker. To do this, DC
from the battery is converted by the amplifier to AC
(alternating current) in the speaker. The ratio of the
power delivered to the speaker and the power taken
from the battery is the efficiency of the amplifier. In
a class A amplifier (transistor on over entire cycle),
the maximum Theoretical efficiency is 0.5 or 50%. In
-4-
TESTING - SECTION 1
a class B amplifier (transistor on for ½ cycle), the
maximum theoretical efficiency is 0.785 or 78.5%.
Since transistor characteristics are not ideal in a pure
class B amplifier, the transistors will introduce
crossover distortion. This is due to the non-linear
transfer curve near zero current or cutoff. This type
distortion is shown in Figure 1. In order to illuminate
crossover distortion and maximize efficiency, the
output transistors of the audio amplifier are biased
on for slightly more than ½ of the cycle, known as
class AB. In other words, the transistors are working
as class A amplifiers for very small levels of power
to the speaker, but they side toward class B
operation at lager power levels.
In this test, you will produce a clicking sound by
shorting the bottom volume control pin to ground using
your finger.
You should hear a clicking sound every time the
pins are shorted. If you hear no sound then;
r Check that U2 and C18 are installed in the
correct position as marked on the PC
board.
r 1. Install a new 9V battery into the battery holder.
Turn the power switch on and turn the knob
fully clockwise. The LED should light.
r Check the potentiometer R6 and the
speaker. Make sure the speaker’s wires are
soldered correctly and not shorting
together.
If LED does not light;
Make sure the diode D2 and LED D3,
capacitor C2, and U2 are mounted in the
correct position as marked on the PC
board.
Figure 1
CIRCUIT DESCRIPTION
amplifier then follows, amplifying only one of those
signals - the one whose frequency is equal to the IC
- followed by the limiter, the demodulator, mute
control circuit, and pre-audio amplifier. The FM-88K
is an auto-scan radio containing two switches, scan
“S” and reset “R”. Tuning is done by using a varactor
diode (D1) instead of a tuning gang found in most
radios. The varactor’s capacitance is changed by
varying the DC voltage supplied to its anode over
resistor R3.
The model FM-88K is a monophonic FM receiver
made on base TDA7088T IC, as shown in the
schematic diagram (Figure 2). The circuit contains
two ICs, speaker, two coils, and a few other
components. The IC TDA7088T (U1) (depending on
the manufacturer, may be type SC1088, SA1088,
CD9088, D7088, or YD9088) is a surface mount,
bipolar integrated circuit of a proper FM
“superheterodyne” receiver. The IC contains a
frequency-locked-loop (FLL). The station signals led
from the telescopic antenna to the input circuit
consists of L1, C5, C6 and C7. It is a parallel
oscillatory circuit damper with resistor R4. Inside IC
signals are led into the mixer, where they are given
a new carrier intermediate frequency. The IF
Voltage reference chart for U2 LM386
Check that resistor R1 is the correct value.
Pin #
Voltage
Pin #
Voltage
Check if the battery is properly installed in
the battery holder and that the power switch
is operational.
1
2
3
4
1.3
0
0
0
5
6
7
8
4.5
9.0
4.5
1.3
Check capacitors C3 and C17.
r 2. Touch the bottom and mounting pins with one
finger as shown in Figure H. You may need to
wet your finger.
Voltage Regulator Circuit
Check the following voltages.
r 1. Voltage across D2 and D3 should be 2.6V
r 2. Voltage across the LED D3 should be 1.9V.
This is how the tuning is performed:
When switch S1 “S” (Scan) is pressed and released,
a positive voltage is applied to the input of the Tuning
Search circuit pin 16. Capacitor C14 starts charging
and the voltage on pin 16 increases. This voltage is
Turn the power switch off and remove the battery from
the holder.
SCHEMATIC DIAGRAM FM-88K
Figure H
FM RADIO HIGHLIGHTS
1. The FM broadcast band covers the frequency
range from 88MHz to 108MHz.
5. The number of times the carrier frequency
changes in a period of time is exactly equal to the
audio frequency.
2. FM signals are usually limited to line a sight.
6. The bandwidth assigned for FM is 200kHz.
3. Audio signals up to 15kHz are transmitted on the
FM carrier.
Figure 2
-5-
4. The amount that the RF carrier changes frequency
is determined by the amplitude of the modulating
signal.
-10-
ASSEMBLE COMPONENTS TO THE PC BOARD
Place a check mark
transferred through resistor R3 to the anode of the
varactor diode D1 (BB910), causing its capacitance
to decrease. Decreasing the capacitance of D1
increases the frequency of the local Oscillator (VCO).
in the box provided next to each step to indicate that the step is completed.
The Oscillator voltage and signals of all the other FM
stations (Fs) from pin 11 are inputted into the Mixer.
The output of the mixer is only FM signals whose
frequencies are equal to the differences of the
oscillator and the original station frequency.
C1 - 100μF, Electrolytic
(see Figure D)
R2 - 18kΩ 5% 1/4W Res.
(brown-gray-orange-gold)
C13 - 680pF Discap
(681 or 680)
Equivalent Schematic and Connection Diagrams
VS
6
15kΩ
7
BYPASS
15kΩ GAIN
8
Only a signal whose carrier frequency is equal to
IF can reach the “Demodulator”. Selectivity (ability
to “pick out” one station while rejecting all others)
is accomplished by two active filters made from the
capacitors connected to pins 6, 7, 8, 9 and 10). The
oscillator frequency increases until the condition
Fo – Fs = 70kHz is accomplished. When this
happens, the charging of the capacitor is halted by
the command that is sent into the “Tuning Search”
circuit by two detectors (diode-blocks) located in
the “Mute Control” circuit.
D1 - BB909/BB910 Varactor
(see Figure G)
C17 - 0.1μF Discap (104)
Figure G
Your kit contains one of two types of
varactor. Use the figure that
corresponds to your varactor style
for mounting instructions.
Mount the varactor flush to the PC
board with the printed band in the
same direction as marked. Solder
and cut off excess leads.
Beveled
edge
0.05”
0.3”
-OR-
r Install speaker
Step 1
+
Step 2
Step 3
Pad
PC board marking
Backing
r Install battery holder
Bend the leads of the battery holder as shown.
Fasten the battery holder to the PC board with a
M1.8 x 7.5mm screw and M1.8 nut. Solder the leads
to the PC board pads as shown.
Outer edge of
PC board
Backing
Speaker
M1.8 x 7.5mm Screw
Step 1: If the speaker pad has
center and outside pieces, then
remove them. Peel the backing
off of one side of the speaker
pad and stick the pad onto the
speaker.
Battery holder
Foil side of
PC board
Step 4
Step 2: Remove the other
backing from the speaker pad.
Step 3: Stick the speaker onto
the solder side of the PC board.
Solder
Step 4: Solder two 1½” wires
from the speaker to the pads
+SP and –SP.
-9-
1½” wires
PC board
(foil side)
GAIN
1
15kΩ
5
VOUT
150Ω
1.35kΩ
2
3
– INPUT
+ INPUT
50kΩ
50kΩ
4
GND
Dual-In-Line and Small Outline Packages
GAIN
In order to hold the frequency, the voltage on pin 16
must not change until the “Scan” switch is pushed
again. That is the function of the AFC (Automatic
Frequency Control) circuit; controlling the voltage on
pin 16.
Printed band
M1.8 Nut
Capacitor C20 is a bypass and necessary for an
amplifier with a high gain IC. Capacitor C18 blocks the
DC to the speaker while allowing the AC to pass.
– INPUT
+ INPUT
GND
When the switch S2 “R” (Reset) is pushed, the
capacitor C14 is discharged, the voltage on pin 16
drops down to zero, and the receiver is set to the low
end of the reception bandwidth 88MHz.
1
8
2
7
3
6
4
5
GAIN
BYPASS
VS
VOUT
Top View
Figure 3
Typical Applications
Capacitor C23 and resistor R2 filter out the radio
frequency component of the signal, leaving a clean
audio signal. Capacitor C22 couples the audio signal
to the input of the power amplifier. Since the
maximum operating DC voltage of the U1 is 5V, the
battery voltage must be regulated down.
Components D2, D3, R1, C1, C17 and C* make up
that circuit.
Amplifier with Gain = 20
Minimum Parts
VS
2
1
8
5
LM386
VIN
10kΩ
6
–
3
+
7
+
.05μF
4
10Ω
Figure 4a
Our kit uses the standard design for the audio amplifier
on base of the integrated circuit (U2) LM-386, or
identical. In Figure 3, you can see equivalent schematic
and connection diagrams. To make the LM-386 a more
versatile amplifier, two pins (1 and 8) are provided for
gain control. With pins 1 and 8 open, the 1.35kΩ
resistor sets the gain at 20 (see Figure 4a). The gain
will go up to 200 (see Figure 4b) if a capacitor
(capacitor C21) is placed between pins 1 and 8. The
gain can be set to any value from 20 to 200 if resistor
is placed in series with the capacitor. The amplifier with
a gain of 150 is shown in Figure 4c. The amount of gain
control is varied by potentiometer R6, which also varies
the audio level and, consequently, the volume.
2
6
–
1
LM386
VIN
10kΩ
Amplifier with Gain = 200
10μF
+
VS
3
7
8
5
+
+
.05μF
4
BYPASS
10Ω
Figure 4b
Amplifier with Gain = 150
VS
2
3
1
7
-6-
8
5
+
4
Figure 4c
+
10μF
6
–
LM386
VIN
10kΩ
47Ω
+
10Ω
BYPASS
.05μF
CONSTRUCTION
SECTION 1
• Turn off iron when not in use or reduce temperature setting when
using a soldering station.
Introduction
The most important factor in assembling your FM-88K Auto-scan FM
Radio Kit is good soldering techniques. Using the proper soldering iron
is of prime importance. A small pencil type soldering iron of 25 - 40 watts
is recommended. The tip of the iron must be kept clean at all times
and well-tinned.
• Tips should be cleaned frequently to remove oxidation before it becomes
impossible to remove. Use Dry Tip Cleaner (Elenco® #SH-1025) or Tip
Cleaner (Elenco® #TTC1). If you use a sponge to clean your tip, then use
distilled water (tap water has impurities that accelerate corrosion).
Solder
ASSEMBLE COMPONENTS TO THE PC BOARD
Place a check mark
Safety Procedures
For many years leaded solder was the most common type of solder used
by the electronics industry, but it is now being replaced by lead-free solder
for health reasons. This kit contains lead-free solder, which contains
99.3% tin, 0.7% copper, and has a rosin-flux core.
• Always wear safety glasses or safety goggles to protect
your eyes when working with tools or soldering iron,
and during all phases of testing.
• Be sure there is adequate ventilation when soldering.
Lead-free solder is different from lead solder: It has a higher melting point
than lead solder, so you need higher temperature for the solder to flow
properly. Recommended tip temperature is approximately 700OF; higher
temperatures improve solder flow but accelerate tip decay. An increase
in soldering time may be required to achieve good results. Soldering iron
tips wear out faster since lead-free solders are more corrosive and the
higher soldering temperatures accelerate corrosion, so proper tip care is
important. The solder joint finish will look slightly duller with lead-free
solders.
'
• Locate soldering iron in an area where you do not have to go around
it or reach over it. Keep it in a safe area away from the reach of children.
in the box provided next to each step to indicate that the step is completed.
D3 - Red LED
(see Figure A)
Figure A
Mount the LED flush to
the PC board with the flat
side in the same direction
as marked.
Flat
D2 - 1N4001 Diode
(see Figure B)
R1 - 680Ω 5% 1/4W Res.
(blue-gray-brown-gold)
PC board marking
• Do not hold solder in your mouth. Solder is a toxic substance.
Wash hands thoroughly after handling solder.
C2 - 220μF, Electrolytic
(see Figure C)
Assemble Components
C3 - 0.1μF Discap (104)
In all of the following assembly steps, the components must be installed
on the top side of the PC board unless otherwise indicated. The top
legend shows where each component goes. The leads pass through the
corresponding holes in the board and are soldered on the foil side.
Use only rosin core solder.
Use these procedures to increase the life of your soldering iron tip when
using lead-free solder:
• Keep the iron tinned at all times.
C20 - 22μF, Electrolytic
(see Figure D)
R5 - 10Ω 5% 1/4W Res.
(brown-black-black-gold)
DO NOT USE ACID CORE SOLDER!
• Use the correct tip size for best heat transfer. The conical tip is the
most commonly used.
What Good Soldering Looks Like
C19 - 0.047μF Discap (473)
Types of Poor Soldering Connections
U2 - 8-pin IC Socket
U2 - LM-386 IC
(see Figure E)
A good solder connection should be bright, shiny, smooth, and uniformly
flowed over all surfaces.
Soldering Iron
1. Solder all components from the
copper foil side only. Push the
soldering iron tip against both the
lead and the circuit board foil.
Rosin
Component Lead
Foil
3. Allow the solder to flow around the
connection. Then, remove the
solder and the iron and let the
connection cool. The solder
should have flowed smoothly and
not lump around the wire lead.
R6/S3 - Potentiometer
Nut & Washer
Knob
(see Figure F)
Soldering iron positioned
incorrectly.
Circuit Board
2. Apply a small amount of solder to
the iron tip. This allows the heat to
leave the iron and onto the foil.
Immediately apply solder to the
opposite side of the connection,
away from the iron. Allow the
heated component and the circuit
foil to melt the solder.
C18 - 220μF, Electrolytic
(see Figure D)
1. Insufficient heat - the solder will
not flow onto the lead as shown.
Soldering Iron
2. Insufficient solder - let the solder
flow over the connection until it is
covered.
Use just enough solder to cover
the connection.
Solder
Foil
Solder
Gap
Component Lead
Mount the diode flush to the PC board
with the printed band in the same
direction as marked.
Printed band
Solder
3. Excessive solder - could make
connections that you did not
intend to between adjacent foil
areas or terminals.
Soldering Iron
Solder
PC board marking
Figure C
4. Here is what a good solder
connection looks like.
Figure F
Polarity mark
Electrolytics have a polarity marking
indicating the (–) lead. The PC board is
marked to show the lead position.
Cut the tab off of the potentiometer as shown.
Insert the potentiometer into the PC board
holes, from the foil side, as shown. Place the
washer over the shaft and tighten the nut.
Solder the potentiometer into place and then
insert the knob onto the shaft.
Warning:
If the capacitor is connected with incorrect (–)
polarity, or if it is subjected to voltage
exceeding its working voltage, it may heat up
and either leak or cause the capacitor to explode.
(+)
Cut tab
Knob
Potentiometer
Foil
4. Solder bridges - occur when
solder runs between circuit paths
and creates a short circuit. This is
usually caused by using too much
solder.
To correct this, simply drag your
soldering iron across the solder
bridge as shown.
Figure D
Figure B
Soldering Iron
Mount capacitor C2 on the back of the
PC board in the location shown. Make
sure the lead with the polarity marking
is in the correct hole as shown.
Polarity mark
(+) marking
Foil
Figure E
Insert the IC socket into the
PC board with the notch in
the direction shown on the
top legend. Solder the IC
socket into place. Insert the
IC into the socket with the
notch in the same direction
as the notch on the socket.
Foil side of
PC board
Washer
Legend
side of
PC board
Notch
Drag
Solder
-7-
Nut
-8-
Shaft