Motorola 880 Service Manual page 57

#8 NPU Repair Procedure
No CE signalling present at pin 26 and 27 of U702 and U705 respectively.
If there are no CE (chip enable) pulses being sent from U701 to the software chips
U704 and U705 it means that U701 is not trying to communicate with the EPROMs.
• Check that U701, U704 and U705 are not physically damaged, have no dry joints
and are positioned correctly. If none of the mentioned problems are apparent,
replace U704 and U705.
If replacing the above components does not eliminate the fault, return the PCB to a
Motorola Hi Tech Center.
#9 NPU Repair Procedure
No signalling present at pins 39 and 40 of U702.
If there are no RAM1CS or RAM2CS (1&2 chip select) pulses being sent from U701
to the SRAM chip U704, it means that there is a problem in communication between
U701 and the RAM.
• Check that U701, and U702 are not physically damaged, have no dry joints and are
positioned correctly. If none of the mentioned problems are apparent, replace
U702.
If after replacing all the above components the fault is still apparent, return PCB to a
Motorola Hi Tech Center.
#10 NPU Repair Procedure
No OE+ signalling present at pin 1 U705.
If there are no ROM2OE pulses being sent to the EEPROM U705, it means that there
is a problem in communication between U701 and the EEPROM.
• Check that U701 and U705 are not physically damaged, have no dry joints, and are
positioned correctly. If none of the mentioned problems are apparent, replace
U705.
If after replacing the mentioned chips the fault is still apparent return the PCB to a
Motorola Hi Tech Center.
12/9/97 68P09403A50
Troubleshooting
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