Nokia NHM-4 Series Assembly, Disassembly And Troubleshooting Instructions page 55

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Keypad
faults 2
Are LK 4
module keys OK ?
Yes
END
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No
Try change LK 4
Is it working now ?
No
Check X303
Measure
ROW0 to ROW4
lines from X303
Are these
~1.8V ?
Yes
Measure
COL1–4 lines
Are these
~ 0 V ?
Yes
Press one key.
Pulses must be in all
ROW and COL lines.
If not, change
first Z301, then UPP
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Yes
Retest
Check ROW0 –
No
4 Lines, X303.
If OK change
Z301. If still fail
change UPP
Change Z301
No
If still fail,
change UPP
1+0
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