HTX-10 pll problem?

[codecxbox]

Upon studying the cpu, I not having any signal on the VCO input pin..which I think and as Nomad suggested, 1 signal has to go in to be compared and internally mixed with the internal 4.5MhZ signal to produce a 16.2× Mhz sig for the charge pump?

 

[brandon7861]

Upon studying the cpu, I not having any signal on the VCO input pin..which I think and as Nomad suggested, 1 signal has to go in to be compared and internally mixed with the internal 4.5MhZ signal to produce a 16.2× Mhz sig for the charge pump?

If turning L14 changes the frequency, the VCO is active.

If that signal, the VCO signal, is not getting back to the CPU, then look at whats between those two points. The buffer Q39. I don't really see a way to kill that transistor but it does have one electrolytic capacitor associated with it, maybe check that. If that cap shorted, the buffer won't work.

And i think that cap failing could explain the warble if the buffer output was losing strength and right at the detection threshold of the CPU/PLL.

Edit: its C123

 

[codecxbox]

good afternoon.. C123 game out good at 103. But I saw that C131 is not there, seems it broke off..

If turning L14 changes the frequency, the VCO is active.

If that signal, the VCO signal, is not getting back to the CPU, then look at whats between those two points. The buffer Q39. I don't really see a way to kill that transistor but it does have one electrolytic capacitor associated with it, maybe check that. If that cap shorted, the buffer won't work.

And i think that cap failing could explain the warble if the buffer output was losing strength and right at the detection threshold of the CPU/PLL.

Edit: its C123

 

[brandon7861]

good afternoon.. C123 game out good at 103. But I saw that C131 is not there, seems it broke off..
View attachment 72253

That might be a problem! Whats the deal with so many SMD parts being missing? They don't just fall off on their own. Look closely to see what else may be gone.