PRELIMINARY SERVICE CHECKS (Continued)
SERVICE CHECKS
MATCH THE NUMBERS ON THE INTERCONNECTING DIAGRAM AND PHOTOS WITH
THE NUMBERS ON THE SERVICE CHECKS TO BE PERFORMED.
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COMPUTER DEAD
(A) Check for 17.5VAC between Connectors A1 and
A2. If the voltage is missing at Connectors A1
and A2, check Power Transformer (T1) for an
open winding. Also check for continuity be-
tween the center tap of the Power Transformer
secondary winding and Connector A3. Check for
an open power cord.
(B) If the voltage is correct at Connectors A1 and A2,
check for 5.0V at the 5.0V source. If 5.0V is miss-
ing, check Resistor R2, check for 5.2V at the
emitter of Transistor Q1. If the voltage is pres-
ent at the emitter of Q1, check Resistor R2.
(C) If the voltage is missing at the emitter of Q1,
check Transistor Q1 and IC1 .Also check Diodes
D3 and D4. Check Power Switch (SW1).
If all of the voltages are correct, refer to the
"Microprocessor Operation" section.
MICROPROCESSOR OPERATION
(A) Computer is dead. Check for pulses at pins 34
and 35 of the CPU IC (IC9). If pulses are missing,
check the SAM IC (IC22) by substitution.
(B) If pulses are present at pins 34 and 35 of IC9,
check for data pulses on pins 24 thru 31 of IC9
when the Computer is turned On. If there are no
data pulses present, check IC9 by substitution.
(C) If data pulses appear on pins 24 thru 31 of IC9
and then suddenly stop, check RAM ICs (IC14
thru IC21), ROM IC(IC12)and Expansion RAM IC
(IC13) by substitution.
VIDEO
(A) No video. Check the Video Display Generator IC
(IC8) and the RF Modulator by substitution.
(B) Dots are missing from alphanumeric characters.
Check (IC8) by substitution.
(C) Wrong characters appear on the screen. Check
Latch IC (IC5) and IC8 by substitution.
COLOR
(A) No color. Check for 3.579MHz at pin 7of SAM IC
(IC22). If the 3.579MHz signal is missing, check
1C22 by substitution.
(B) If the 3.579MHz signal is present at pin 7 of IC22,
check the RF Modulator by substitution.
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(C) Colors are not correct. Check for afrequency of
3.579MHz at pin 7of SAM IC (IC22). If the fre-
quency is not correct, check the adjustment of
Clock Trimer TC1, see "Miscellaneous Adjust-
ments". Also check IC22 by substitution.
SOUND
(A) No sound. Type in and run the following pro-
gram:
10 SOUND 200,200: GOTO 10
Check for pulses at pin 1of DAC IC (IC3). If the!
pulses are present, check the adjustment of the|
Sound Coil, see "Miscellaneous Adjustments"
(B) If pulses are not present at pin 1of IC3, check fori
pulses at pins 3thru 8of IC3. If the pulses are|
present, check IC3 by substitution.
(C) If the pulses are missing at pins 3thru 8of IC3,
check PIA IC (IC2) by substitution.
KEYBOARD
(A) Keyboard is dead. Check the keyboard Connec-
tor (CN2) for good connections.
(B) If the keyboard connector checks good, check
for pulses at pin 11 of Decoder IC (IC11). If
pulses are missing, check IC11 by substitution.
(C) If pulses are present at pin 11 of IC11, check PIAJ
IC (IC7) by substitution.
(D) Agroup of keys do not work. Check the
keyboard Connector (CN2) for good connec-
tions. Also check IC7 by substitution.
CASSETTE
(A) Cassette motor will not run or runs all the time.
Check Relay RY1 contacts between pins 1and 3
of Connector JK4. If the cassette motor will not
run, check for continuity between pins 1and 3
while saving aprogram on tape or loading apro-
gram from tape. If the cassette motor runs all of
the time, check for ashort (relay contacts stuck).
(B) If Relay RY1 checks good, check PIA IC (IC2) by
substitution.
(C) Programs cannot be saved on tape,
and DAC IC (IC3) by substitution.
Check IC2
(D) Programs cannot be loaded from tape.
IC2 and SALT IC (IC1) by substitution.
Check
III
