Chapter 6 Vhf Troubleshooting Tables; Troubleshooting Table For Receiver; Table 6-1. Troubleshooting Table For Receiver - Motorola EP450 Service Manual

Chapter 6 VHF Troubleshooting Tables

6.1

Troubleshooting Table for Receiver

Symptom Possible Causes
Radio Dead (no 1. Battery dead or defec-
turn-on beep, no tive.
LED indication)
2. Defective battery con-
tacts.
3. Blown fuse
4. DC switching fault
5. Microprocessor not
starting up.
6. Regulator fault

Table 6-1. Troubleshooting Table for Receiver

Substitute known good battery or
battery eliminator.
Inspect battery contacts for corrosion
or bent terminals.
Check voltage on each side of fuse.
If blown, 0 VDC after fuse.
Verify battery voltage present at
S444 pin 5 when radio is on.
Verify Q494-1 is at least 1 V dc,
Q494-6 is ~0.1 V dc, Q493-3 is at
Vbatt.
Verify clock input to U401-90
(EXTAL) is 7.3975 MHz using high
impedance probe. If clock is 3.8
MHz, check for shorts on U401 pins.
Connect RIB to verify communica-
tion via CPS.
Verify U401-94 (RESET) is high.
Verify U310-5 is 5 V dc, U320-5 is
3.3 V dc, U330-5 is 3 V dc.
Procedure Corrective Action
Charge or replace battery.
Clean/repair/replace J301.
Check for short on output,
check D301, VR301, trouble-
shoot/repair as needed, replace
fuse.
Check/replace on-off-volume
control S444.
Troubleshoot/replace Q493/4.
Verify 16.8 MHz signal at U451-
34. If OK, troubleshoot/replace
U451. If not present, trouble-
shoot U201 Synthesizer. Repro-
gram/reflash as needed.
If RESET is Low, troubleshoot
regulator U320. Check for
shorts at U401 pins. Replace
U401. Reprogram as needed.
Check for shorts on outputs,
troubleshoot/repair as needed,
replace faulty regulator.