Motorola Gm Series Detailed 6864115b62 A Manual

Controlhead Model for GM380, and GM12802-9
prevents radio circuitry from discharging this capacitor. The +5V at the second anode of D0855 
speeds up charging of C0856, when the host radio is turned on by a high level at the ignition input 
while the supply voltage is applied to the radio. This prevents the microprocessor from accidently 
entering bootstrap mode.
4.3 Power On / Off
The On/Off/Volume knob when pressed switches the radio’s and the controlhead‘s voltage regulators 
on by connecting line ON...

2-10THEORY OF OPERATION
controlhead µP can drive the line. The microprocessor sends serial data via pin 79 and D0872 and it 
reads serial data via pin 78. Whenever the microprocessor detects activity on the BUS+ line, it starts 
communication.
When the host radio needs to communicate to the controlhead µP, it sends data via line BUS+. Any 
transition on this line generates an interrupt and the µP starts communication. The host radio may 
send data like display information, LED and back light status or it...

Controlhead Model for GM380, and GM1280 2-11
output of the op-amp to rise and to reduce the base to emitter voltage of Q0943. This decreases the 
current of Q0941 until the loop has settled.
The back light for the LCD module uses a similar circuitry. The only differences are that µP port PH2 
controls the back light brightness and that the LED’s are located on the LCD module which is 
connected via J0821. Control line BL A GREEN connects to the anodes and control line BL K 
GREEN connects to the cathodes...

2-12THEORY OF OPERATION
informs the µP about the pressed PTT button. The µP will inform the host radio about any status 
change on the PTT IRDEC line via SBEP bus.
When line PTT IRDEC is connected to FLT A+ level, transistor Q0851 is switched on through diode 
VR0851 and thereby pulls the level on line ON OFF CONTROL to FLT A+ level. This switches on the 
radio and puts the radio’s µP in bootstrap mode. Bootstrap mode is used to load the firmware into 
the radio’s flash memory (See controller sub section...

Chapter 3
TROUBLESHOOTING CHARTS
1.0 Controlhead GM140/340/640 Troubleshooting Chart
1.1 On/Off 
Radio can not be switched on via ON/OFF Volume 
NO
YES
YES
NO R0823 Pin TAB
= 5V ?
R0823 Pin TAB1
when pressed
= 5V ?Check / Replace 
Volume Pot R0823
Check / Replace
R0822 / VR0822 / 
D0822
NO
YES
J0801 Pin 2
> 10V ?Check / Replace
Q0821
Check / Replace
Q0822 / R0821
YES
NO
J0801 Pin 2
=5V ?Check / Replace
D0821 / R0852
Press and hold
On/Off Volume Knob 

3-2TROUBLESHOOTING CHARTS
1.2 Microprocessor 
Power Up Alert Tone is OK but volume knob 
does not operate and no indicator is on
NO
YES
YES
NO
YES
NO
YES NO
YES
EXTAL
U0831 Pin 31
= 8.00 MHz ?
RESET
TP0833
= HIGH ?Check / Replace
C0833 / R0832 / U0831
Check radio controller Data Signal
on J0801 Pin 5
BUS+ ?
Data Signal 
on TP0836
SCI_RX ?
NO
Data Signal
on TP0837
SCI_TX ?
Check / Replace
R0831 / U0833 / U0831
Check / Replace
R0837 / R0836
Check / Replace
U0831
Check / Replace
D0831 / R0838
Measure with...

Controlhead GM160/360/660 Troubleshooting Flow Chart 3-3
2.0 Controlhead GM160/360/660 Troubleshooting Flow Chart
2.1 On/Off 
Radio can not be switched on via ON/OFF Volume Knob
NO
YES
YES
NO
R0823 Pin TAB
= 5V ?
R0823 Pin TAB1
when pressed
= 5V ?Check / Replace 
Volume Pot R0823Check / Replace
R0822 / VR0822 /
D0822 / C0822
NO
YESJ0801 Pin 2
> 10V ?Check / Replace
Q0821
Check / Replace
Q0822 / R0821
YES
NOJ0801 Pin 2
=5V ?Check / Replace
D0821 / R0852
Press and hold
On/Off Volume Knob 

3-4TROUBLESHOOTING CHARTS
2.2 Microprocessor
Power Up Alert Tone is OK but volume knob does 
not operate and no indicator is on
NO
YES
YES
NO
YES
NO
YES NO
YES
EXTAL
U0831 Pin 31
= 8.00 MHz ?
RESET
TP0833
= HIGH ?Check / Replace
C0833 / R0832 / 
Check radio controller Data Signal
on J0801 Pin 5
BUS+ ?
Data Signal
on TP0836
SCI_RX ?
NO
Data Signal
on TP0837
SCI_TX ?
Check / Replace
R0831 / U0833 / U0831
Check / Replace
R0837 / R0836
Check / Replace
U0831
Check / Replace
D0831 / R0838
Measure with scope...

Controlhead GM160/360/660 Troubleshooting Flow Chart 3-5
2.3 Display
Power Up Alert Tone is OK, volume knob does operate,
indicator/backlight is on but nothing on display
YES
NO
YES
NO
V5 (against 5V)
TP0973 between
-6V and -7V ?
Activity on
Address & Data lines
A0 / D0..D7 / CS1
of U0971?Check for shortage
U0831 / U0971
Check LCD Assembly
Check / Replace
C0971 / C0973 / R0972
R0973 / R0974 / U0971 

3-6  TROUBLESHOOTING CHARTS
2.4  Backlight 
Power Up Alert Tone is OK, volume knob does operate,
YES
NO
Check for shortage
YES
NO
Check / Replace