President Washington 8719 PLL cannot align frequency

[Lkaskel]

Hi Everyone,
I truly hope everyone is well during this challenging time!!

So, someone dropped of a President Washington (3 button) 8719 PLL and asked for an alignment. The radio had a channel conversion that was in the process of being removed and variable power. I removed the 4 wires from the PLL going to 2 separate switches as the owner said he no longer wanted the extra channels. The 4 wires went to pins 10, 11, 12 and 18 of the PLL. I did not find any cut traces. I began the alignment and step 5 is to adjust CT3 to 34.9875 as read on TP1. The initial reading is 34.35*****. It's way off of 34.98***. CT3 does not bring it anywhere close as expected. Any thoughts? Why 600K low?

Thanks as always!!

 

[nomadradio]

Pin 10 of the the 8719 should have been grounded from the factory. If you removed a wire from this pin, that suggest that it is no longer bonded to ground.

Try that.

73

 

[ExitThirteen]

That depends on if the loop mixer crystal was changed. If the loop mixer crystal is 11.1125, then pin 10 of the MB8719 PLL needs to be grounded. If it has an 11.325, or 11.3258 crystal in it, then pin 10 needs to be isolated from ground. Since there are no cuts on any traces at the PLL, the mixing crystal has to be 11.1125 for the radio to have the proper 40 channels.

I suspect a botched channel mod, as the stock 11.1125 mixing crystal will only allow lowers to be installed in the radio, with the exception of 27.415-27.445.

Double check the loop mixer crystal, which will be located just right of the PLL. If it's an 11.1125, you're good to go. If it's an 11.325, or 11.3258, change it out to an 11.1125, make sure pin 10 of the PLL is indeed grounded, and check for your 34.9875. Hope this helps.


~Cheers~

 

[Lkaskel]

Ok, so once again....you all are amazing!! The person that did the channel mod had cut the lead on pin 10 just before it went through the board. I missed that. It did have the 11.1125 crystal (it looks newer) and once I grounded pin 10 the alignment went well. It is amazing how far it was out but I am unsure what they were actually looking for and what equipment they used. I will say this, I am truly blessed to have such a great freq counter with 11 digit resolution and to have you all on here to enable me to accomplish what I can.

Thanks as always!!!