BENCH TESTING
RELATED SECTIONS:  BLOCK DIAG RF PATH and DIGITAL (J12 test point)

Do not connect the tuner to the radio.  Connect a 13.8 Volt regulated Power Supply directly to the power terminals on the PCB, as shown on the picture (negative =  black, positive = red).  CAUTION: AH-3 has no overcurrent protection so set the current limit on your Power Supply to 2A or put a 2A fuse in line.  You do not need to connect anything to START and KEY terminals at this time.  Also, no RF input and termination is required.

After applying DC power to the unit you should hear several relay clicks and the current consumption should settle around 600 mA. The tuner has two voltage regulators:

 

AH-3 voltage regulators
 Schematic Ref IC 19 IC 20
 Test Point output pin CP9  J12 (see DIGITAL)
 Output Voltage + 8 V + 5 V
 Part number M78L08 M8705
 Power for IC 14, IC 15, IC 17

IC 1

4.0 Volt analog bias voltage is derived from + 8 Volt line.
Note that the relay drivers IC 10, 11, 12 and 13 (Darlington pairs) are not supplied from + 5 V line.


DEFAULT STATE:  After power-up, all relays should default to a RF bypass path, which you may verify by probing voltages on  J5, J6 and CP17:
J5 (inductors)
PIN # VOLTAGE
1 13.8 V (source)
2 0 V (not connected)
3 0.8 V
4 0.8 V
5 0.8 V
6 0.8 V
7 0.8 V
8 0.8 V
9 0.8 V
10 0.8 V
11 0.8 V
12 0.8 V

J5 and J6 headers
NOTE:  pin numbers in tables correspond to numbers
in yellow on the above photo

J6
(capacitors)

PIN # VOLTAGE
1 13.8 V
2 13.8 V
3 13.8 V
4 13.8 V
5 13.8 V
6 13.8 V
7 13.8 V
8 13.8 V
In the default state, the voltages on J5 pins 3 to 12 should be all low (about 0.8 V), corresponding to all relays enabled, shunting the series inductors. Note that the  0.8 Volts is the output voltage across a saturated Darlington pair (not zero Volts!).   At the same time, voltages on J6 pins 1 to 8 should be all high (and equal to your set Power Supply voltage).  This means that all parallel capacitors are disconnected.

The CP17 (top left corner on the picture below) default state is high (13.8 V), which indicates that relays RL1 and RL2 are disengaged.

CP 17 location

Uploaded: 29 Dec 2000