After Sales
Technical Documentation
RAE/RAK–1N
Faultfinding/Disassembly
Page 8 – 15
Original, 05/97
1.1.1.3 Undervoltage lockout removed?
This UVLO is made as hardware limit to shut down Vsys if battery voltage
drops below 5.0V. When the N82 comparator controlling N81 has
worked the shutdown of Vsys is cancelled only after battery voltage
rises over 6.0V! It is possible to test PDA module at voltages between
5.0V and 6.0V but wakeup of Vsys requires voltage higher than 6.0V. This
hysteresis is put to design to prevent oscillation at low battery voltages
after battery cutoff limit is reached and battery voltage rises after its load is
removed.
If battery voltage is higher than 6.0V, battery voltage (nearly) should be
seen at regulator N81 pin 1. If not go to 1.1.1.4.
1.1.1.4 UVLO fault
First check that 4.1V can be measured from reference V84 cathode. If not
replace V84 and check R88. Next check that voltage between R87 and
R89 is higher than voltage across V84. This voltage should be reduced to
V84 voltage level if battery voltage is reduces to 5.0V. If not check R87,
R89 and R65.
If above mentioned is OK check R80. If OK replace N82.
1.1.1.5 Vsys OK?
Measure Vsys voltage for example from C84 positive terminal. It should
be between 3.135V and 3.465V. If not go to 1.1.1.6.
1.1.1.6 Check Vsys regulator
First check that battery voltage is seen at N81 pins 3 and 8. If pin 3 is low
regulator does not exit from ’soft start’ state.
1.1.1.7 Is N81 pin 7 toggling?
If measured with oscilloscope there should be seen voltage level toggling
between 0V and VBatt at frequency of about 200kHz. If not go to 1.1.1.8.
Otherwise go to 1.1.1.9. If the regulator has dropped to a shutdown state
the pulse frequency is lower and pulses appear at irregular time intervals.
1.1.1.8 Vsys controller fault
Replace N81.
1.1.1.9 Check V88, L82, C84
If the controller N81 tries to alternate pin 7 level, even at reduced voltage
magnitude the fault is very likely found from V88, L82 or C84. If the
problem is still unsolved check that Vsys current consumption is less than
500mA. Reasonable value is about 200mA when CPU is fully on. If not
there must be a short circuit in Vsys line.
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