President JFK info?

[Cable Guy]

I have one sitting here, is there anything else like it that is better documented? Like a block diagram? I found a schematic and "alignment" but that alignment info seems vague. I am going to check it out tonight and wanted a heads up if anyone knows. I think it's marketed to the french.

 

[sp5it]

Which JFK?

 

[Cable Guy]

The ugly one I guess, I dropped some pics below. PC-713AG board with uPD2816C pll.

 

[Cable Guy]

It may be related to the ?uniden pegasus 3? It needs a complete overhaul to make it usable and I don't think I want to do it unless it's rare. There is a thread on wwdx about it that had some good info, the schematic is impossible to read.

 

[brandon7861]

I found 3 schematics (I know you said you had it, wanted to look anyhow). The Rick Jackson one from CBTricks in blue, another from the zip file referenced in the thread you mentioned above (the one that is hard to read with a 6-pin mic), and one online that someone took colored pencil to. I don't know if the Rick Jackson one is the same as the colored one.

Edit: added the 713 schematic to the other thread

 

[Cable Guy]

Cool, I didn't notice the Rick Jackson one, i will give that a glance. It's listed under president JFK? This is a 4 pin rig. I checked it out some, tp1 is full tilt 8v always, the vco can does change the vco frequency, all 3 loop xtals are working at the oscillator and all within about 200hz. Changing channels does nothing to vco or tx/rx because tp1 (vco) is getting a full send from pll. It does tx and rx at whatever the vco is running at and something strange, the pll shows locked on the ld pin. This thing is in rough shape and I really should clean it and recap before troubleshooting it much. I will look at it more tomorrow.

 

[brandon7861]

CBTricks Rick Jackson schematic

President J.F.K.

Thread with the one I just uploaded

Post in thread 'President JFK (PC-713 Circuit Board)'

Jun 12, 2025

Putting this here for others that search.

• brandon7861

The only 6-pin one I found was the hard to read one.

 

[brandon7861]

Seems like that PLL is experiencing two seperate issues. Changing the VCO with the varactor steady should make it fall out of lock, its not. Thats problem #1. The other problem is that the only way TP1 can have full rail voltage is if pin 19 is open.

This doesn't necessarily mean the PLL is bad, it might simply mean that it isn't getting power. I assume these two pins are open collector, and if the PLL supply is dead, both of these features would be acting like open circuits.

When you get back to it, verify the supply voltage at pin11. I have a hunch it is dead, either from a bad cap, or that zener being shorted.

 

[Cable Guy]

Seems like that PLL is experiencing two seperate issues. Changing the VCO with the varactor steady should make it fall out of lock, its not. Thats problem #1. The other problem is that the only way TP1 can have full rail voltage is if pin 19 is open.

This doesn't necessarily mean the PLL is bad, it might simply mean that it isn't getting power. I assume these two pins are open collector, and if the PLL supply is dead, both of these features would be acting like open circuits.

When you get back to it, verify the supply voltage at pin11. I have a hunch it is dead, either from a bad cap, or that zener being shorted.

Thanks for lending your brain Brandon, I was thinking the pll was bad when I hooked it up last week, but I had to clear the bench for a rush job so I didn't get to follow through. It was getting proper voltage at pin 11 last night so the zener is okay and the caps aren't resistive or shorted. I was getting a divided down frequency on pin 22 although it wasn't in the range specified by Lou in his pll handbook. T/R pin is okay. I checked pin 19 after seeing 8v on tp1, it is the same 8v.

 

[sp5it]

Attached schematic and service manual.

 

[Cable Guy]

Attached schematic and service manual.

Thanks sp5it, I never took French in high school but I think I can figure it out given the usual alignment format and similar words. And it has a block diagram that I can read! That's awesome.

 

[Cable Guy]

Ignoring the lock for the moment, the down mix signal to pin 22 causes the pll to allow full voltage to the vco, and assuming the vco is okay, the divider circuit could be fault. Or the vco or varactor could be fault? I will check that later.
Back to the lock detector, I can't see how the ld pin would stay high unless the pll is bad, it should pull that pin low. Brandon, I think you're right about multiple issues, and I believe the pll is bad for sure. I think I have an old 29ltd parts rig with the same pll.

 

[brandon7861]

Ignoring the lock for the moment, the down mix signal to pin 22 causes the pll to allow full voltage to the vco, and assuming the vco is okay, the divider circuit could be fault. Or the vco or varactor could be fault? I will check that later.
Back to the lock detector, I can't see how the ld pin would stay high unless the pll is bad, it should pull that pin low. Brandon, I think you're right about multiple issues, and I believe the pll is bad for sure. I think I have an old 29ltd parts rig with the same pll.

Sounds like you are right. I think it's bad too if its getting proper supply voltage.

 

[Cable Guy]

Sounds like you are right. I think it's bad too if its getting proper supply voltage.

I swapped out pll's and now tp1 is controllable. I will try alignment and get back.

 

[brandon7861]

If there was a problem with the VCO, it wouldn't change freq with the can. You can test the varactor by connecting a 10k resistor to ground at TP1. It will cut the varactor voltage in half and you should see a freq change that way too.

edit: posted too late, your post just came through