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22. RA-6 Power Supply Troubleshooting
Chapter 22 - RA-6 Power Supply Troubleshooting
General Description
The power generation and distribution has been simplified by utilizing a traditional analog standby supply providing
unregulated B+ for the main AC relay and regulated 5V for the main CPU, NVM and IR receiver (not shown).
More detail on this circuit will be covered later in the shutdown troubleshooting section.
As shown in Figure 22-1, the main power supply consists of a single oscillator circuit (IC6003) with FET drivers
and a single PIT, or Power Input Transformer. Once the unit is powered up and the main relay RY6002 is closed,
current flows through R6002 to minimize the initial surge. RY6003 closes as soon as 11V is generated by the
secondary. If this relay does not close within two seconds, the oscillator will stop since PH6002 monitors this
relay. This will be covered in Chapter 23.
Starting:
Approximately 300VDC will be supplied to Q6006 and pin 18 of IC6003 to start the oscillator. Pin 1 will monitor
the unregulated B+ for excessive or low voltage. IC6003 will begin oscillating and sending square wave signals
out of pins 12 and 16. These drive signals will always be 180° out of phase and at a 50% duty cycle. The IC does
not require feedback from the T6001 to operate. This makes it simpler to troubleshoot since the oscillator can
run on its own as long as start and correct sense voltage is present. Once the supply is running, it will supply its
own stable power source known as VC1 and input it at pin 8.
When pin 16 of IC6003 is high, Q6006 will turn on. 300VDC will be output at the source to C6047 and it will
charge. Current flows through the primary of the PIT entering pin 1 and exiting pin 2. R6076 and R6080 provide
the ground return for the current. Q6005 is off at this time since pin 12 is low. Once pins 12 and 16 reverse
polarity, Q6006 will turn off and Q6005 turns on. A short circuit is placed across the primary windings and C6047
to discharge the capacitor for the next cycle when Q6006 turns on again.
Regulation:
Voltage regulation is maintained via a feedback path to monitor the 135V line for stability. IC501 and photo
optical isolator PH6001 sends this feedback information to pin 2 of IC6003 to vary the oscillator frequency.
Current monitoring enters pin 9 by looking for a voltage drop across R6070 and R6076. The voltage drop at
these resistors is zero to .2VDC. Any higher voltage level will cause the oscillator inside IC6003 to increase in
frequency to reduce voltage output.
Soft Start:
Soft start is accomplished by keeping the oscillator at high frequency for about three seconds at startup. This is
initiated by the charging of C6021 on pin 6 of IC 6003. The initial AC current is reduced by 50% during this time.
This, combined with the durability of the FET drivers, allows the supply to start and let the unit go into protect
mode, preventing damage to Q6005 and Q6006.
