Elenco AM Radio Kit - Manual (Page 34)

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DC Voltages
The voltage readings below should be used in troubleshooting the AM radio. Measure the voltage on transistors
Q4 - Q6 with switch SW2 in the top position. When measuring the voltage on the IC, make sure the switch SW2
is in the down position.
Q1 B 1.5V Q6 B 5.8V
E 1.0V E 5.2V
C 8.9V C 9.0V
Q2 B 1.4V Q7 B 4.6V
E 0.7V E 5.2V
C 8.9V C 0.0V
Q3 B 1.7V U1 1 - 1.3V
E 1.0V 2 - 0
C 9.0V 3 - 0
4 - 0
Q4 B 5.7V 5 - 4.5V
E 5.2V 6 - 9V
C 8.3V 7 - 4.6V
8 - 1.3V
Q5 B 8.3V
E 9.0V
C 5.8V
Test Conditions
1. Volume control set to minimum.
2. Connect a jumper wire between capacitor C2 (side that
goes to red lead of coil L1) to negative battery.
3. Battery voltage: 9.0V
4. All voltages are referenced to circuit common.
5. Voltage reading can vary +10%.
AM ALIGNMENT WITH NO TEST EQUIPMENT
It is best to use an earphone for this alignment
procedure. Rotate the tuning knob fully counter-
clockwise and place the label on the knob with the white
arrow pointing at the 540kHz marking.
With an alignment tool or screwdriver, turn coils L2, T1,
T2 and T3 fully counter-clockwise until they stop. DO
NOT FORCE THE COILS ANY FURTHER. Turn each
coil in about 1¼ to 1½ turns. Set the antenna coil about
1/8” from the end of its ferrite rod. Refer to Figure L on
page 29.
Turn the power ON and adjust the volume to a
comfortable level. Tune the dial until a weak station is
heard. If no stations are present, carefully slide the
antenna back and forth on its ferrite rod and retune the
dial if necessary. With an alignment tool or screwdriver,
adjust T1 until the station is at its loudest. Reduce the
volume control if necessary. Adjust T2 until the station is
at its loudest and reduce the volume control if necessary.
Adjust T3 until the station is at its loudest and reduce the
volume if necessary. Retune the radio for another weak
station and repeat this procedure until there is no more
improvement noticed on the weakest possible station.
This procedure peaked the IF amplifiers to their
maximum gain.
Tune the radio until a known station around 600kHz is
found. It may be necessary to listen to the station until
their broadcast frequency is announced. If no stations
are present at the low side of the AM band, adjust L2
until a station is heard. Once a station is found and its
broadcast frequency is known, rotate the dial until the
white pointer is aligned with that station’s frequency
marking on the dial. Adjust L2 until the station is heard.
Tune the radio until a station around 1400kHz is heard.
It may be necessary to listen to the station until their
broadcast frequency is announced. If no stations are
present at the high end of the AM band, adjust the
oscillator trimmer on the back of the gang. Once a
station is found and its broadcast frequency is known,
rotate the dial until the white pointer is aligned with that
station’s frequency marking on the dial. Adjust the
oscillator trimmer located on the back of the gang until
a station is heard. Repeat these steps until the oscillator
alignment is optimized. This procedure set the oscillator
range at 995kHz to 2055kHz.
Tune the radio for a station around 600kHz. Carefully
slide the antenna back and forth until the station is at its
loudest. Tune the radio for a station around 1400kHz.
Adjust the antenna trimmer located on the back of the
gang until the station is at its loudest. Repeat these steps
until the antenna alignment is optimized. This procedure
set the antenna to “track” the oscillator. Once the
antenna is properly aligned, carefully apply candle wax
or glue the antenna coil to the ferrite rod to prevent it
from moving (as shown in Figure 33).