Troubleshooting Supplements - Motorola 880 Service Manual

Troubleshooting Supplements

Logic/Processing Supplement 1 - Unit Doesn't Power Up (NPU)
START
Apply power to the radio.
Is 6.5V dc
present at
U900 pin 40?
Press the power key to
initiate PCB power up
process. You will have to
press the power key each
time you wish to take a
reading, unless you tie the
watchdog circuitry high
adding a 10k resistor to the
pads at R904.
Are U900
pins 22 and
28 at
+2.75V?
Is 13MHz clk
present at
U201 pin 57?
Is 13MHz clk
present at
U703 pin 17?
12/9/97
NO
YES
NO
YES
NO
YES
NO
YES
1
68P09403A50
Proceed to "#1 NPU Repair Procedure" on page 46.
Proceed to "#2 NPU Repair Procedure" on page 46.
Proceed to "#3 NPU Repair Procedure" on page 47.
Proceed to "#4 NPU Repair Procedure" on page 47.
Troubleshooting
43