Nokia 9000i, Service Manual

Page: 255 / 434

After Sales
Technical Documentation
RAE/RAK–1N
Faultfinding/Disassembly
Page 8 – 13
Original, 05/97
1.1 Vsys OK?
Start the Power–On check by connecting the power supply to the target.
The power supply voltage limits are: 5.8V (min.) – 7.2V (nom.) – 8.5V
(max), The current consumption in a working PDA is typically
about120mA.
If the Vsys is out of the limits (2.97V..3.66V) or the current consumption
differs from the normal, then check the PDA power unit.
1.1.1 Check PDA Power Unit
The following picture illustrates the troubleshooting diagram that can be
used with the PDA power unit malfunctions. As a rough check it is good to
glance through the power section of PDA module and check that there are
no short circuits by alien particles and that no component has ’burning’
signs, especially tantalum capacitors. If yes, the fault is most probably
cured by replacing that component. In such a case it is recommended
that the complete power unit check is done after replacing the faulty
component.
If power unit check is not solving the problem there is a possibility that
battery line or some regulator output has a short circuit somewhere. Vsys
is distributed all over the board and it may be difficult to find possible short
circuit cause. There are test strips going to the edge of PCB in middle
layers. The strips are cut when the module is cut from the panel in
production. If the device is used in high moisture environment it is
possible that those copper strip ends corrode and form some ohmic short
circuit to neighbouring strips. Use of glass fibre brush to test strip ’necks’
on the edge of PCB is recommended. Current supplying capabilities of
different regulators are: Vsys:500mA, VCC5:50mA, LCDVEE:5mA. Each
current is for the specific regulator output voltage. VCC5 is linear
regulator, VSYS and LCDVEE are made by switch mode regulators.
1.1.1.1. Input filter OK?
Between board–to–board connector battery line and regulators there is
LC–filter to reduce interference conducting through battery line from CMT
to PDA module and visa versa. Overcurrent and overvoltage may
damage filter components. If battery voltage is not seen in equal value at
positive terminal of C83 and at board–to–board connector battery line
then check that L80 is not open circuited. If not check that C81 and C83
are not short circuited to a finite resistance (<100 ohm) and there is no
visible damage in capacitors. If fault is still not found check also bypass
capacitors C93, C94, C96, C87 and C97.
1.1.1.2 Input filter fault
Replace faulty component. If fault is not focused try to change tantalum
capacitors first. If that is not helping there is a possibility that one of the
IC’s N80, N81, N82 or N83 has internal short circuit.