Colt 357A PLL Problem C5121

[SuperLid]

I have no experience with this PLL and there are no service docs that I can find, apart from a datasheet for the C5121. This leaves me with some questions, that hopefully someone with experience knows the answers to.

1: The channel selection is stuck on channel 9. No up or down changes.

2: The radio does receive signals and will change when the VCO tuning is changed.

3: What is the unlock pin voltage level supposed to be when unlocked?

4: What is the VCO voltage when tuned and from where is the test point?

5: This radio has never worked correctly. It was given to me a long time ago and I just found it. I figured I would try it.

Thanks,

SL

 

[19wrc333]

Sorry, I don't know the PLL.
Curious that it is stuck on channel 9, does it have a channel 9 switch?

The CB PLL databook has the following snippet about that particular PLL.

 

[brandon7861]

I would expect the VCO voltage to be around 2/5 of whatever the PLL supply voltage is (at ch20). 2/5 instead of 1/2 because varactors move more at lower voltage and moving it down gets it more into the linear-ish range where the pF's move more with voltage (centers the range of the varactor that way).

 

[brandon7861]

I wonder how close it is to the DNT contact 2
nevermind, thats an FM radio.
Looks the same and has the same pll

 

[sp5it]

It is CMOS pll. Fragile to static etc...
If crystal is OK, then PLL is dead.
Mike