PC-385 PCB

Stalker IX, Realistic TRC-490, Uniden / President Washington, Cobra 142GTL and others that use the PC-385 PCB

If you know of others please let me know !


I decided to write this alignment information down when I got a Uniden (President) Washington in for repair and servicing, I only had some sketches and notes available from when I had worked on the same type of radio before, I needed to work out the whole alignment procedure, that is why I wrote this page.


GENERAL ALIGNMENT INFO


All adjustments are made with the radio set radio to CH19 on the FCC band unless otherwise stated.

Make sure that the clarifier is centered.

You will need:

DC Voltmeter (or a Digital Multimeter)

A good frequency counter with a 10Hz resolution.

The proper (plastic / ceramic) adjustment tools.

A 50MHz oscilloscope (although a 30MHz will do).


Loop oscillator alignment:


 

Attach frequency counter to TP1 (R157)which is located directly next to L27.

Double check that the clarifier is centered before starting !

 

Mode

Adjust

Frequency

Comments

AM

L20

34.985

LSB

L19

34.9825

USB

CT3

34.9875

TX frequency

VR3

34.985

Check during TX on AM

 

Re check all of the frequencies again at this point, they can alter after adjusting the other points.


Offset oscillator:


Attach frequency counter to TP3 (R101) which is located in the middle of the PCB towards the rear, next to TR13.

Mode

Adjust

Frequency

Comments

AM

L17

27.185

Check at antenna socket during TX (do this last)

LSB

CT2

7.7975

USB

CT1

7.8025

Re check all of the frequencies again at this point, they can alter after adjusting the other points.


VCO alignment:


Connect DC Volt meter / oscilloscope to TP9 (top leg of R72, just below the VCO card)

Set radio to channel 1 on the lowest band, adjust L13 so that the base voltage just lifts (should be set to around 2.0 VDC).

Check that the radio will transmit at the set voltage, if not adjust L13 to increase it a little until it does transmit.

Go to channel 40 on the highest band (or the highest channel available), check that the voltage is below 6.8 VDC and that the radio will transmit.


VCO output alignment:


Connect oscilloscope to TP1 (left leg of R184, just above L13, L14)

Adjust L14 for maximum reading.


Loop mixer alignment:


Connect oscilloscope to TP10 (left leg of R193, just above L20)

Adjust L18 for maximum reading.

 


TX mixer cans:


L26, L27

 


TX alignment cans:


L28, L29, L36 (do not adjust L39 as it is the low pass filter trap, for RFI reduction)

 


Driver and final bias adjustments:


Bias of

Adjust

Amperage

Comments

Driver

VR8

30mA

Test at TP8

Final

VR9

50mA

Test at TP7

 

To check the driver and final amplifier bias adjustments set the radio to USB without any mod, use an ammeter to check for the correct bias current.

To locate the test points follow the wire that comes from just below VR8, it will go to the other side of the PCB, it has a special plug that is connected to a pin, this pin is TP8 (as marked on PCB), to test the driver bias just pull the wire from TP8 and connect the ammeter between TP8 and the wire that was removed.

After adjustment connect the wire back to TP8

Directly next to TP8 is TP7, this is the test point for the final bias, use the same procedure as above, just connect the meter between TP7 and the wire that goes to it.


TX power alignment:


Attach an RF power meter and dummy load to the radio.

Adjust VR6 for 4 Watts.

Check that power is equal at each end of the band (CH1, CH40)

 


AMC alignment:


After performing the AMC mod which installs a 1 KOhm preset pot (or just changing the resistor) to increase the AM modulation level the modulation percentage must be checked.

Attach the oscilloscope to the antenna socket and set the scope to the audio range (about 0.5 mS/ Div).

Inject a 100mV 1KHz signal into the mic socket, adjust for 95% modulation.

 


RX alignment:


Adjust these metal cans for the maximum RX signal (make sure the signal used is only very weak otherwise the AGC will activate and cause problems)

Inject a 1 KHz modulated RF signal on 27.185 MHz into the radios antenna socket.

Adjust L10, L9, L8, L7, L6, L5 for the highest reading on the radios signal meter.

 


IF alignment (for RX as well):


Adjust these metal cans for the maximum RX signal (make sure the signal used is only very weak otherwise the AGC will activate and cause problems)

Set the radio to USB.

Inject an unmodulated RF signal on 27.185 MHz into the radios antenna socket.

Adjust the clarifier for the highest reading.

Adjust L3 and L4 for the highest reading on the radios signal meter.


Signal meter alignment:


Increase the RF generator output to 100uV.

Adjust VR1 for a reading of S9 on the signal meter.

 


Noise blanker alignment:


Turn on noise blanker switch.

Connect DC Volt meter / oscilloscope to TP6 (right leg of R9, just below L2)

Adjust L1 and L2 for maximum voltage reading (will be around 60mV).

 


List of adjustments:


 

VR1 Signal meter
VR2 Squelch
VR3 TX Frequency
VR5 Carrier balance
VR6 AM power
VR7 ALC
VR8 Driver Bias
VR9 Final Bias
VR10 RF power meter
VR12 Modulation meter
L1 Noise blanker
L2 Noise blanker
L3 I.F. 1st stage
L4 I.F. 2nd stage
L5 RX (6th stage)
L6 RX (5th stage)
L7 RX mixer output (4th stage)
L8 RX (3rd stage)
L9 RX (2nd stage)
L10 RX (1st stage)
L13 VCO
L14 VCO output
L17 AM offset frequency
L18 Loop mixer
L19 LSB loop frequency
L20 AM loop frequency
L26 TX mixer input
L27 TX mixer input
L28 TX mixer output (1st stage)
L29 TX (2nd stage)
L36 TX
L39 RFI low pass filter trap
CT1 USB offset frequency
CT2 LSB offset frequency
CT3 USB loop frequency

 


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