Uniden Washington Channel Mod Issues

[Dave Whitehead]

HI Guys,

I am brand new here and I'm not a tech. Let me first thank you all for any help you may be able to give me. I am grateful there are websites like this to possibly help with great people like you all!! My issue is this. I have a Uniden Washington , 5 pin mic that I am trying to make channel mods on. The PLL is the 8719. The research I found for this radio is using 2 spst switches. Cutting the trace on pin 10 of the PLL and solder 1 of the spst switches on each side of the cut on that trace. Then 2nd spst switch is to be soldered between pins 11 and 12 on the PLL. I have done all that. Solder joints look good. Don't see any issues with that. I have looked several times.
My problem is I've lost my regular 40 channels some how. The switch between pins 11 and 12 seem to work changing frequencies as I understand it should. If I understand the modification correctly I should have several channels below and several channels above. I do have the channels above. I did replace the 11.1125 crystal with the 11.3258. I have no idea what to check on getting my original 40 channels back. What could I be overlooking? There has to be something that I've done that I'm not seeing. Again thank you so much for any suggestions, comments, help!!!!!

added: The switch used to bridge the trace cut of pin 10 of the PLL doesn't do anything. Switch seems to be in good working order.

Dave

 

[TM86]

I'm hoping you have a volt meter handy. Check the voltage on pin 10 with the switch in one position, then the other. In one position you should have somewhere around +5 to +8 volts on that pin. In the other position you should have 0 volts (or ground) on that pin. If you find that you have 0 volts or +5 volts (or more) in both positions, then you need to recheck you soldering, or ohm out your switch (with the radio power off!) to make sure it isn't shorted or open.

Since this radio originally had a 11.1125 MHz crystal, on the other side of the cut trace at pin 10 it should probably be a positive voltage all the time. When you switched to the 11.3258 MHz crystal I think it should be 0 volts to get the "normal" 40 and +5 to get the "extra" channels, but I haven't played with a MB8719 in years so I may have that backwards.

 

[nomadradio]

Yep.. Gotta know the identity of the PLL's loop crystal first. Two frequencies were used in the Uniden SSB CB radios with the 8719 PLL chip.

These two crystal frequencies each produce a set of channels that are 64 channels apart one from the other. A radio built with the 11.1125 crystal will have pin 10 soldered to a ground foil.

A radio built with the 11.325 crystal will have no connection to pin 10 at all. There is an internal resistor called a "pull up" that forces this input pin to a logic high state until you ground it.

Changing your radio from the 11.1125 crystal it was built with to the other one is the fast way to put upper channels above channel 40 in the radio. The original crystal would get you mostly just lower frequencies below channel 1.

If you have the 11.325 crystal, you'll need to switch any connection to pin 10 OFF to obtain channels 1-40.

73

 

[TM86]

Go with what Nomad said, he works on this stuff all the time so I'm sure it's fresher in his mind than it is in mine.

 

[Dave Whitehead]

Thank you guys. I very much appreciate your advice!!!