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16. RA-5A Power Supply Troubleshooting
PH6005
OPTICAL
ISOLATOR
N
CH
N
CH
IC6002
DRIVER
MCZ3001D
16
12
9
15
18
2
6
8
10
14
1
2
C6099
1
IC6107
ERROR DET.
uPC1093C
3
1
AC
RECT.+
FROM
IC6001/1
(D BD.)
R6099
0.47 OHMS
R6007
R6098
R6097
R6096
R6092
C6093
VC1 VC2 VB F/B
OCP
R6095
+
+
T6004
Q6008
Q6007
TIMER
R6084
R6083
R6163
R6164
D6130
C6017
6.5V
SOURCE
D6115
D6183
7V SOURCE
11V
SOURCE
V
SENSE
FIGURE 16-2 - PRIMARY POWER SUPPLY RA-5A CHASSIS
340VDC
160V
3V
1.86V
D6007
18.4V
4
2
15
10
11
14
14
11
6
7
C6045
R6165
C6116
R6162
D6050
D6048
D6051
D6049
C6086
C6085
Vcc TO
IC6001/
PIN 8
R6082
R6081
16.2TVP14 1465
6/13/02
A BOARD
Activating the oscillator is accomplished by closing the main power relay RY6001 when the set is turned on. This
will provide approximately 340VDC to Q6008, a startup voltage to pin 18 of IC6002 along with a sample of the
unregulated B+ to pin1. Once the IC receives voltage at pin18 and the divided-down sample at pin 1 is 1.7VDC
or greater, the oscillator will run and output drive signals as long as the incoming AC voltage is higher than
70VAC.
When pin 16 of IC6002 is high, Q6008 will conduct and send the unregulated B+ to the primary of T6004.
Current will flow and charge C6017 through R6083 and R6084. Q6009 is off at this time due to the low at its gate.
Once the drive signals reverse phase, Q6009 will turn on and discharge C6017 while Q6008 is off. Current is
monitored at R6083 and R6084 and input to pin 9 of IC6002. The voltage at this point is zero under normal
operating conditions. A rise above .2V causes the oscillator to run at high frequency. Since the shift to high
frequency may alleviate the over-current condition, a fluctuation of normal to high frequency bursts can occur.
Regulation is accomplished by monitoring the 6.5V source at the secondary by IC6107. The voltage monitored
at pin 1 is inverted at pin 3. The pull-down of the cathode of the LED inside PH6005 will control light output to the
phototransistor. This will be output at pin 1 and sent to IC6002 pin 2. Any rise in the 6.5V line will cause the
phototransistor to pull down IC6002 pin 2, causing the oscillator frequency to increase.
Soft start is accomplished by keeping the oscillator at a high frequency during initial turn-on. This minimizes the
initial current surge by charging filters. The charging of C6093 at pin 6 of IC6002 initiates the soft start and
reduces the initial AC current approximately 50%. This initial current limiting, combined with the durability of the
FET drivers, allows the supply to survive direct shorts on the secondary lines before the protect circuits react.
Once the oscillator is running, it will provide power to itself via pin 6 of T6004. This voltage is rectified and filtered
to supply 20VDC to pin 8 of IC6002 and place the oscillator in full running condition. This same voltage will
continue on to the secondary supply and will become one of the “must haves” for it to operate.