Radio Shack HTX-400, Service Manual

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30
TROUBLESHOOTING CHART
SYMPTOM PROBLEM REMEDY
Unit does not work at
all 1. Defective power switch VR101
2. Defective INPUT POWER LINE / REGULATOR 1.Replace
2.Replace
No output from speaker
at all 1. Defective external speaker jack
2. Defective IC3,Q111,113,114 & Speaker 1.Replace or repair
2.Replace defective
component
No noise on speaker 1. Measure all the voltage of IC601, IC401, VR101
2. Defective Squelch circuit components
VR101
1.Replace
2.Replace
No modulation 1. Poor audio output and defective modulation
Microphone amplifier components(IC806,807)
2. Defective RV802
1.Replace
2.Replace defective
components
LCD display does not
work 1.Defective X801, IC801 1.Replace
No TX output power 1. Defective
Q101, Q102, Q103, D101, RV101, L108, L105 1.Replace
ERROR MESSAGES
PROBLEM REASON CHECK POINT COUNTER MEASURE
EEP-ROM
Error No 3V input to the 8th
pin of IC802 Check if 3V input is applied to
the 8th pin of IC802 If this problem happens,
1. Turn the power off
2. Press "FUNC+MO" keys
3. Turn the power on
4. Release "FUNC+MO" keys
PLL Error VCO unlock 1. When Q501 collector is
locking, check the "LOW"
2. Check if the VCO locking
voltage is normal or not
3. Check if the output voltage
of Q604/Q603/Q602 is
normal or not
4. Check if the output voltage
of IC601 is 3V or not
5. Check if the output level of
the 4th pin of VCO is
normal or not
Check & Replacement
S-Short Short of external
speaker output
terminal Check the voltage of
CPU Pin 41
Protect On : High
Off : Low Check