Motorola 880 Service Manual page 56

Dual Band 880/890 (DCS/GSM)
#5 NPU Repair Procedure
The +2.75V dc supply is missing at one or more of pins 45, 46, 58, and 59 of U701.
• Check that there are no dry joints on U701.
• Inspect for broken traces and/or lifted pads on U701.
#6 NPU Repair Procedure
The reset line at pin 30 of U900 does not go high to +2.75V dc.
• Check that U900 is not physically damaged, has no dry joints, and is positioned
correctly. If none of the mentioned problems are apparent replace U900.
If replacing U900 the fault is still apparent return PCB to a Motorola Hi Tech Center.
#7 NPU Repair Procedure
The watchdog line at pin 31 of U900 does not go high to +2.75V dc.
The watchdog line is pulled high by U701 when it receives and executes the initial
blocks of software from the PROM's U704 and U705. If there is a problem with either
U701, U702, U704, or U705 the watchdog will not be pulled high. This will cause
U900 to power down the +2.75V regulator's and halt the power up process.
• Check the CE lines of U702 and U705 respectively for activity.
• If there is no activity, proceed to NPU repair procedure 8.
• If above activity is present, check for activity of RAM 1 CS and RAM 2 CS at U702.
• If there is no activity, proceed to NPU repair procedure 9.
• If above activity is present, check the OE+ line at pin 1 of U705 for activity.
• If there is no activity, proceed to NPU repair procedure 10.
If the above procedures don't eliminate the fault, return the PCB to a Motorola Hi
Tech Center.
48 68P09403A50 12/9/97