Explaination of the ATAS-100 Remote Unit circuit. By Chris N0TTW
================================================================== This information is provided for the convenience of trouble shooting the ATAS-100. This explaination only deals with the control board and not the matching network.
Please refer to the ATAS-100 Technical Supplement in the FILES section of yahoo group YaesuATAS ( http://groups.yahoo.com/group/YaesuATAS/ ) before proceeding. These files are listed as ATAS100Tech.zip or the individual page listed as ATAS100Tech1.jpg.
Disclaimer:
The following procedures can possibly void your warranty.
**************Use these procedures at your own risk.***************
Of course I am NOT responsible for any damage caused by disassembly, or any other general messing around with this antenna or your radio, enough said. ===================================================================
HOW TO BREAKDOWN THE CIRCUIT:
The Remote Unit consists of 3 sections, Regulated Power Supply, Voltage Sensing and Motor Control. I will try my best to explain each section as we go along.
REGULATED POWER SUPPLY: The power supply consists of a RF Filtering circuit (C1012, L1001, L1002), and the Regulated Power Supply (C1001, C1002, C1003, C1004 and Q1001). The RF Filtering removes most of the RF and provides the circuit with just the DC voltage to power the circuit. The DC voltage is further filtered by the capacitors around the 6V regulator Q1001. Q1001 provides 6V to the Voltage Sensing OP-Amps (Q1002) and the Motor Control IC (Q1003).
VOLTAGE SENSING: The circuit consists of 3 voltage dividers. One on the input (R1001 and R1008) and 2 connected to the 6V supply (R1002, R1006 and R1003, R1007). The two voltage dividers provide approximately 3.5V (R1002, R1006) and 3V (R1003, R1007) for the Q1002.
Q1002 is an 8-pin IC that has 2 Op-Amps setup as comparators. Voltage from Q1001 is provided to pin 8. Pin 4 is grounded. Input voltage from the input voltage divider is placed on pins 3 (ANT UP) and 6 (ANT DOWN). Comparing voltages are placed on pins 2 and 5. C1006, C1009 and C1010 are used to help remove stray RF from the inputs. The outputs of the Op-Amps are pins 1 (ANT UP) and 7 (ANT DOWN). C1007 and C1011 remove stray RF from the outputs. R1004 and R1005 are pull-up resistors for the outputs. Both pins 1 and 7 are high when the circuit is energized.
MOTOR CONTROL: Motor control is handled by a Fujitsu Bidirectional Motor Control IC, Q1003. VCC is supplied to pins 7 and 6. Pins 2 and 3 are grounded. Pin 1 and 4 are motor control logic pins. Motor drive is done from pins 8 and 5. C1008 is used to filter any RFI/EMI from the motor. C1005 filters stray RF from the power supply.
The Logic table (from the spec sheet) for the IC follows:
Pin1 * Pin4 * Motor Condition Pins 5 and 8 ******************************************** VCC * VCC * Motor Braked (output shorted) <-- ******************************************** |-- MOTOR STOP GND * GND * Motor Open (Standby) <-- ******************************************** VCC * GND * Motor Forward (Pin 5 VCC) ******************************************** GND * VCC * Motor Reversed (Pin 8 VCC) ********************************************
THEORY OF OPERATION: In theory, the lowest voltage at the antenna to go UP is around 10V. Any lower, and the antenna doesn't function properly. Basically the antenna either just sits there or goes down.
When DC voltage is applied from the radio or manual tuner, RF is filtered, and DC is placed across the input voltage divider and the voltage regulator.
6 volts is supplied to both ICs and the two voltage dividers for the each comparator circuit. The Op-Amps gets the 3.5V from R1002/R1006 to pin 5 and Pin 2 gets 3V from R1003/R1007.
Next thing that happens depends on what voltage is present on the coax. Let us use a voltage example of 8 Volts.
If 8V is placed on the coax connector, the voltage from the input voltage divider (R1001/R1008) sends a voltage of 3V to pin 6 and 3. The top comparator looks at and compares the voltage from pin 3 to pin 2's voltage (3V). Pin 1 then goes HIGH/VCC causing Q1003 Pin 4 to go HIGH/VCC. The bottom comparator see the 3V on pin 6 and compares it to the voltage on pin 5 (3.5V). This causes Pin 7 to go LOW/GND, placing Pin 1 on the Q1003 at LOW/GND. Based on the logic table, the motor is reversed (down)
Now if we applied 10V instead, the voltage from the input divider would be 3.53 volts. This would cause a reverse state on pins 1 and 7. Causing the motor to go forward, raising the antenna.
PROBLEMS WITH THE CIRCUIT THAT COULD FAIL: There are some possible failures to this circuit. So I'll list them by location number.
C1002: I noticed that C1002 is only rated at 10V in the parts list, while the schematic shows it to be 50V. This may become a future problem if it is actually 10V and not 50V. Voltages can exceed it with short runs of coax (less than 50 feet) and cause anything from leaking electrolyte to exploding. If at anytime you dissassemble this antenna, check this cap for leakage. Replace with, at minimum, a 25V SMT cap.
Q1003: I noticed no current limiting resistor on the output of this IC. If the motor is jammed or frozen, the current will exceed its rating easily. This will cause the IC to fail. If this IC is damaged, check the motor with 5 volts first before replacing the IC.