[DSP-10] PLL locking and voltages at L21

[kd7ts]

At 02:32 AM 12/31/2008, you wrote:
>Hi all
> 
> After getting by the loading of software and other tests, im wondering if anyone can help
> 
>I have 9.1v at L21, is it best to run the udiag2.exe then go back and test the voltage here to see if I can get a locked status?
> 
>Thanks Chris
>_______________________________________________


Hi Chris,

Just some general observations of the circuit around Q4 and U6. Q4 runs from the 5 volt regulator, U13. There should not be any voltage higher than 4.8 to 5 volts in that area. The tuning voltage to the varactor comes from U6 which runs from the 10 volt regulator.  This tuning voltage is appled across L20 and might be anything between  some very small voltage, near zero, to almost the full 10 volts. 

It seems likely L20 is where you are seeing 9.1 volts, which, if true, is nothing extraordinary. And... if this is the case, it means the PLL (U7) wants to run the frequency down as it thinks the frequency it is comparing against, on Fin (pin 4 of U7), is lower than where Q4 is oscillating. Tuning C69 through it's range might be useful if it happens that everything else is working. Adding more C lowers the oscillator freq. It might require some change to the toroid inductor to get this right. It is also possible that U7 is not being programmed with the correct data and the frequency in the U7 registers is just nuts. 

A frequency counter can be very useful here to confirm oscillation and frequency. I don't recall what frequency this comes up on, but I think the tune up procedure covers this.

Do you have the screen displaying on the computer ? Does the clock in the lower left corner update ? We don't care if the time is correct, for now, we just need to know that it updates. The ability to change the displayed frequency on the screen demonstrates some functionality of the serial communications between the display and the EZKIT. 

Do you have the EZKIT or the KDSPX ? There is an error in the KDSPX wiring depending on how old your diagrams are, but I don't think it affects this symptom.

Just got your last message as I was about to send this....

All of the above applies... could the voltage requlator U13 be installed backwards ?? Where is this voltage coming from ?? As I recall the sillk screen for both of the PLL  regulators is incorrect. Might be... Check U103 as well !!

73 Mike KD7TS

Cut from ...http://www.proaxis.com/~boblark/dsp10.htm

Important! - The silk-screen legend is backwards for the 78L05 regulators, U13 and U103. The flat sides of both TO-92 packages should be towards the top of the board. There is no problem in installing the parts, of course. The sketch of the package included with the board is correct. Thanks to KD7TS for catching this. (Added 26 Oct 99)