Nokia 9000i, Service Manual

Page: 262 / 434

After Sales
Technical Documentation
RAE/RAK–1N
Faultfinding/Disassembly
Page 8 – 20
Original, 05/97
1.3.1 Reset OK?
The PWRGOOD signal, coming from the PDA power unit, should go from
low to high after 140ms when VBatt is connected. If this signal is not
functioning as expected, then disconnect the signal either from the CPU
(D130) or the Reset IC (D80), and isolate the problem to the power unit or
to the CPU.
If this signal rises too fast, or the signal levels are illegal, then check the
power unit. If the signal is OK, but there’s no bus activity at all, then
suspect a CPU fault, see 1.3.1.1
1.3.1.1 CPU Fault
If the PLL is running properly and the CPU gets the RESET signal from
the power unit (PWRGOOD), but there is no bus activity at all, then it is
likely that the CPU is not functioning properly.
If the PLL circuitry surrounding the CPU is OK, but the PLLDIV24 is not,
then it is likely that the CPU is defective.
It is possible that PLLDIV24 is OK as well as RESET but no activity is
detected on CPU address lines. Before you replace the CPU it is
reasonable to check that circuitry around the HPLLI (R137, C153, C154)
and IREFH (R139) is OK. It is hard to measure these signals so a visual
check is usually all that can be done. If no defect can be found, suspect a
defective CPU chip.
If the device beeps during POST CPU related error beeps, then it’s likely
that the CPU is defective.