PC-833 PCB

President AR144, AX144, Uniden PC-244
and others that use the PC-833 PCB

If you know of others please let me know !


I decided to write this alignment information down when I converted a President AR144, 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.

UPDATE

A visitor to my site sent me some more information and clarifications on the correct alignment procedure for this radio, unfortunately I have lost his details since he contacted me, I have updated this page to match the corrections he pointed out.


GENERAL ALIGNMENT INFO


All adjustments are made with the radio set radio to CH19 on the FCC or NZ RFS23 band unless otherwise stated. (alignment detials for the NZ band are also included)

Make sure that the clarifier is centered

 

You will need:

A good frequency counter with a 10Hz resolution

The proper (plastic / ceramic) adjustment tools.

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


Offset oscillator alignment:


Attach frequency counter to TP3 (bottom leg of R105, to the left of L6)

Double check that the clarifier is centered before starting !

 

FCC Band alignments

Mode

Adjust

Frequency

Comments

AM

L16

16.490

 

LSB

L18

16.4875

 

USB

L17

16.4925

 

TX frequency

VR3

16.490

Check during TX on AM

 

NZ Band alignments

Mode

Adjust

Frequency

Comments

AM

L16

15.85500

 

USB

L17

15.85750

 

LSB

L18

15.85250

 

TX frequency

VR3

15.85500

Check during TX on AM

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


Carrier oscillator:


Attach frequency counter to TP5 (right leg of R34) which is located to the right of X2 below TR18

Mode

Adjust

Frequency

Comments

AM

L19

27.185 (FCC) /
26.550 (NZ)

Check at antenna socket during TX (do this last)

LSB

L21

10.6925

 

USB

L20

10.6975

 

Another method which has been suggested is shown here:

Disconnect the transmitter by removing the vertical PCB connecting the driver and modulator DC supplies (TP6, TP7 & TP8).

Connect the frequency counter to TP9 (D19, beside the SSB Crystal Filter)

Unbalance the Double Balanced Modulator (IC3, AN612) by joining pin 1 to earth (usually by using your multimeter on diode test through the BE junction of TR24, making it conduct to earth).

On AM Transmit, adjust L19 for 10.69500 MHz

On USB Transmit, adjust L20 for 10.69750 MHz

On LSB Transmit, adjust L21 for 10.69250 MHz

 

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 TP2 (top leg of R93, just to the left of L14)

Set radio to channel 40 and adjust L14 for 4.5 VDC.

Set radio to channel 1, check that the voltage is above 1.8VDC, if required adjust L14, go to channel 40, check that the voltage is below 8.0 VDC and that the radio will transmit.

 


VCO output alignment:


Connect oscilloscope to TP3 (bottom leg of R105, to the left of L6)

Adjust L15 for maximum reading.

 


Offset oscillator filter (tripler) alignment:


Connect oscilloscope to TP4 (left leg of R34, to the right of L13)

Adjust L13 for maximum reading.

 


TX mixer alignment:


Carefully align L39 and L40 for maximum transmitter output on AM with the transmitter DC supply reconnected. 

 


TX alignment:


Carefully adjust L38, L37 and L27 for maximum transmitter output on AM. 

 


Carrier Balance alignment:


Connect the oscilloscope to the Antenna Socket using a 10x probe.

Set Mike Gain to minimum.

Carefully adjust VR4 on USB transmit with no modulation for minimum transmitter output visible on the oscilloscope. Check on LSB, if noticeably larger, adjust VR4 so that it is at a minimum for both (and relatively equal). 

 


Driver and final bias adjustments:


Bias of

Adjust

Amperage

Comments

Driver

VR9

25-30mA

Test between TP8 and TP7

Final

VR8

45-50mA

Test between TP8 and TP6

 

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 test remove the shorting PCB at the rear of the radio, test between the points listed above, then replace the PCB.

his reading will vary as the transistors warm up, hence the reading window of 5mA. It is important that there is no modulation applied to the SSB transmitter whilst making these readings, the carrier oscillator and the Carrier Balance (VR4) has been adjusted before adjusting the bias.


TX power alignment:


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

Adjust VR10 for an unmodulated average carrier power of 4 Watts.

Check that the unmodulated average power is equal at each end of the band (CH1, CH40). It should be at least 3.7 Watts.

 


ALC alignment:


Connect a RF Wattmeter and dummy load to the antenna socket.

Set The Mike Gain Control to Maximum.

Inject a 50mV 1KHz signal into the microphone socket, adjust VR6 for 12 Watts Peak Envelope Power on Ch 19 USB Transmit. 

Confirm on Ch 1 & 40 that the output Power is still between 11 and 12 Watts PEP.


AMC alignment:


Connect a modulation meter (or oscilloscope) and dummy load to the antenna socket.

Set the Mike Gain control to Maximum.

Inject a 30mV 1KHz signal into the microphone socket.

Adjust VR5 for 95% modulation.


Tx Meter Alignment:


On AM Transmit (un-modulated), Adjust VR7 for the 4W marking on the meter. 

 


RX alignment:


Make sure the signal used is very weak otherwise the AGC will activate and cause problems.

Adjust these metal cans for maximum received signal, take into consideration both the signal displayed on the signal meter and the audio volume, strictly speaking it should be adjusted purely on volume.

Inject a 1 KHz 30% AM modulated RF signal on 27.1850MHz (FCC) / 26.55000 MHz (NZ) into the radios antenna socket.

Set the RF Gain control to maximum.

Adjust L3, L4, L5, L6, L7, L8, L9 and L10 on AM for the highest reading on the radios signal meter. Adjust the signal generator to keep the tuning effect obvious on the meter (as you go through the alignment, reduce the output of the signal generator).

Tip - Detune L9 whilst adjusting L3 to L8 and L10 to make the peaking more obvious, then peak L9 last.

 


Signal meter alignment:


Increase the RF generator output to 100uV unmodulated.

Ensure the RF Gain control is fully clockwise.

On AM adjust VR1 for a reading of S9 on the signal meter.

 


Squelch alignment:


Keep the RF generator output at 100uV.

Set the Squelch and RF Gain Controls Fully Clockwise.

On AM adjust VR2 counter clockwise until the squelch opens, then adjust it clockwise until it just closes.

 


Noise blanker alignment:


Turn on noise blanker switch.

Set RF Gain control fully clockwise.

Connect High Impedance DC Volt Meter to TP1 (bottom leg of D2 to the right of L2)

Adjust L1 and L2 for maximum voltage reading.

 


List of adjustments:


 

VR1 Signal meter
VR2 Squelch Preset
VR3 TX frequency
VR4 Carrier balance
VR5 AMC (AM Modulation)
VR6 ALC (SSB Power)
VR7 RF power meter
VR8 Final bias
VR9 Driver bias
VR10 AM power
L1 Noise blanker Amp Input
L2 Noise blanker Amp Output / Detector
L3 RX Input Coupling
L4 RX Band Filer (1st stage)
L5 RX Band Filer (2nd stage)
L6 IF Filter 1 st stage
L7 IF Filter 2nd stage
L8 IF Filter 3rd stage
L9 IF Filter 4th stage
L10 IF Filter 5th stage / Detector
L13 Offset Oscillator Filter
L14 VCO
L15 VCO Buffer
L16 AM Offset frequency
L17 USB Offset frequency
L18 LSB Offset frequency
L19 AM Carrier frequency
L20 USB Carrier frequency
L21 LSB Carrier frequency
L27 TX (3rd stage)
L37 TX (2nd stage)
L38 TX mixer output (1st stage)
L39 TX mixer input
L40 TX mixer input

 


List of test points:


 

TP1 Noise blanker
TP2 VCO Control Voltage
TP3 VCO output
TP4 Offset Oscillator Filter
TP5 Carrier oscillator Output
TP6 Transmitter DC Supply (Bias common)
TP7 Driver Bias Measurement point
TP8 Final Bias Measurement point
TP9 Double Balanced Modulator Output

 


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