DAK IX receive problem channels 1-13

[Jimbo165]

I have a Dak IX works good transmits on all 40 channels. It receives good on all channels except channels 1-13 all of these channels do not receive just a muffled sound . Any ideas on what to do ??? Thanks

 

[sp5it]

Start with measuring VCO voltage on TX ch1

 

[Jimbo165]

sp5it I cannot find any info on voltages and where to check them on the Dak. It has the MC145106 pll in it . But do not know exactly how to find just channel 1 to check TX voltage? Channel selector board is numbered 1-8 on back and I can see PLL chip. Sorry not exactly sure.

 

[sp5it]

http://www.cbtricks.com/radios/dak/mark_ix/

PLL CIRCUiT ALIGNMENT PROCEDURE:

1. Set transceiver in Transmit mode.

2. Connect oscilloscope D.C. probe to T.P. 1

3. Adjust L403 and observe the D.C. level swing between zero volts to 8 VDC. Then set the level at 7VDC when channel selector is set at Channel 40, (Note when channel selector is switched to 1. the level will jump to about 3-4VDC.)

4. With frequency counter measure VCO frequency at P408 against the chart. As an example, the channel 1 Transmit VCO should be 16.543 MHz. When changed to channel 1 Receive mode, the VCO frequency will be 16.27 MHz.

 

[Jimbo165]

Thank You sp5it i had put it back on shelf but will get it back down and check and compare those voltages. It transmits and receives great on all other channels and It transmits fine on channels 1-13 but will not receive on channels 1-13. Wouldn't a out of alignment affect all channels not just the 1-13 receive? I picked up radio at a garage sale it really looks nice do not want to sell it would just like to see it working stock and not do a board change.

 

[sp5it]

Do you have freq meter? Measure VCO output on ch1, should be 16.543MHz. P408 from PLL board.
I would check mc145106 truth table...
http://www.s-and-m-software.co.nz/cbsim/ choose your PLL in that software and check if logic state is as it should.
Mike

 

[nomadradio]

Had a problem with the PLL in this model when it first hit the market 40-plus years ago. Setting L403 for the proper VCO tuning voltage was impossibly "touchy". The radio would lock over a range or 20 to 30 channels only, but not the full 40.

The fix was to cut the foil trace that leads to pin 2 of IC401 on the PLL circuit board. It's the MC145106 chip. A 100pf disc capacitor is bridged across the cut in the foil trace.

Improves the range of channels that the chip will lock onto properly.

Got a lot of business from other CB shops when the word got out we could fix this 'factory feature' of the radio.

73