Motorola 880 Service Manual page 44

Dual Band 880/890 (DCS/GSM)
Table 6: GSM Receiver Troubleshooting and Repair Chart
RX Symptom
1. Portable tele-
phone exhibits
poor reception
and/or erratic
operation
(such as calls
frequently
dropping,
weak and/or
distorted
audio, etc.).
2. Receive audio
is weak and/or
distorted.
36
Probable Cause
a) Antenna assembly is
defective.
b) Defective or mis-phased
RF/Audio-Logic Board.
c) Defective keypad board.
(i.e. SEND key won't work)
a) Connections to/from
Keypad/Display circuit
board defective.
b) Earpiece speaker defec-
tive.
68P09403A50
Verification and Remedy
1. Check to make sure that the antenna pins
are properly connected to the Logic/RF
assembly. If OK, substitute a known good
antenna assembly.
2. If the fault is still present, proceed to b.
1. Check for appropriate frequencies and
power level gains/losses in the RX path.
Reference RF Block Diagram.
2. Replace malfunctioning components if
listed on parts list. Likely fail components
are: FL400, FL480, Q410, Q460, Q480, and
U220.
3. If parts replacement doesn't correct the
fault, replace transceiver.
1. Substitute keypad and logic board with a
known good keypad and logic board.
2. If known good board works, place the
keypad from the defective unit onto it and
attempt to function.
3. If unit functions properly, replace the mylar
barrier on the defective unit and then
attempt to function defective unit with orig-
inal keypad.
4. If fault persists, replace the logic board.
1. Gain access to Keypad/Display board as
described in "Disassembly" on page 29.
2. Check connection from earpiece to Keypad/
Display circuit board. Make sure to check
polarity and solderability. If connection is
not at fault, proceed to b.
3. If Keypad/Display board is faulty, examine it
for improper solder and/or connections.
Likely fail components: J500.
1. Gain access to earpiece speaker as
described in "Disassembly" on page 29.
2. Substitute a known good earpiece speaker.
Place a call and verify improvement in
earpiece audio. If good, re-assemble
portable with new earpiece speaker.
3. If earpiece speaker not at fault, re-install
original earpiece speaker and proceed to c.
12/9/97