Comark RF500A/AP Service Manual
Tier 3: RF500A Component Level Repair
Common Power Rail (Pwr)
This is the common power rail, it will always be the input voltage (Either external supply, PoE or battery) less the diode
drop of either D306, D311 or D323 (see respective data sheets for diode drop) depending on the input.
5V Rail
This is the switched power rail mainly for the PC module, it can only be measured by switching the main board on
(press and hold the On/Off switch for 4 seconds). The test limits for this rail are +500mV -200mV.
3VM Rail
This rail is a sub rail of the 5V rail. As such it is only active when the 5V rail is active. This measurement should be
performed at the same time as the 5V. The test limits for this rail are +200mV.
3VC Rail
This rail is always present as long as the battery pack is connected, it provide constant power for the RTC and the
control MPU. The test limits for this rail are +200mV.
Battery Charging
The charging current should be 420mA +100mA, to measure this perform the following steps:
1. Set up a DMM to measure current and place on the mains input between the external PSU and the DUT.
2. Switch on the external mains.
3. If the batteries are not being charged the supply current will be less than 100mA, if this is the case hold the
gate of Q301 at 0V, this will force the battery charging to turn on.
4. Verify the supply current is as specified above.
17 November 2011
Page 41 of 65
Short to 0V
(
if required
)
