[Elecraft] Alignment of VCO - Problem

[Don Wilhelm]

David,

The PLL Reference is apparently OK and your problem is in the VCO itself.
The lack of RF voltage says the circuit is not oscillating - but we cannot
declare Q18 dead just yet.

OK, next step is to check the DC voltages at Q18 - compare with the DC
Voltage chart in Appendix E.

Double check T5 against the diagram in the manual page 55 (leads 1 and 3
should come from the top of the core and the green winding must be in the
same direction as the red winding) - if one of the windings is reversed, the
oscillator will not oscillate.

Check the voltage at the drain of Q17 and compare with the DC voltage
chart - measure the gate and source while you are at it, and just for a bit
of additional information, check the DC voltages at Q16.

Tell us what you find.

73,
Don W3FPR

> -----Original Message-----
>
> I read 12098.20 down to 12084.54 at TP3 in the PLL Reference Oscillator
> Range test.
>
> I checked the windings of T5 very carefully, as well as the resistances
> between pads - they appear correct.
>
> The soldering at T5 and Q18 looks good.
>
> The RF Voltages at Q18 are all zero :-( ... Dead?
>
> DC Voltages at U3:
> Pin 6: 4.02
> Pin 7: 8.02
> Pin 8: 0.00
>
> RF Voltages at U3, Pin 3 & 6 are all zero :-(
>
> On Tue, Nov 14, 2006 at 07:24:04AM -0500, Don Wilhelm wrote:
> > David,
> >
> > Do you read a proper frequency at TP3? Does the PLL Reference Oscillator
> > Range test produce the correct frequencies? (see the manual page 60).
> >
> > If the answer to the above question is YES, then check the
> winding of T5.
> > Be certain the turns are correct and the leads are inserted
> into the correct
> > holes.  Check the tinning and soldering.  Check the soldering in the
> > vicinity of T5 and Q18.  What are the RF Voltages that you read
> at the gate
> > and source of Q18?
> >
> > Check the DC Voltages (compare to chart in Appendix E) at U3.
> What are the
> > RF Voltages at U3 pin s 3 and 6?
> >
> > 73,
> > Don W3FPR
> >
> > > -----Original Message-----
> > >
> > > I don't know. Must be asleep at the switch.
> > > Here's what's what so far this end.
> > > The probe verifies -- it did read correctly in step 3 on page 46.
> > > The leads are correct.
> > >
> > > I have replaced the suspect diode but the probe will not read anything
> > > at TP1.
> > >
> > > I have constructed the RF Probe and connected it to my DMM.
> > > It reads voltages at certain points, but sees nothing at TP1.
> > >
> > >
> >
>
> --
> David Dawson
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