VCO Alignment

[MikeH-3]

Hello all, and thanks to those who responded to my recent message
regarding the PLL reference oscillator test.

I no sooner resolved that issue than I ran into a more puzzling issue
during the VCO alignment. On the initial test, I had reasonable
voltages through the entire band (ranging from 2.066V to 7.95V).
Several high voltages, but most were well within the range. However,
when I tapped the band switch button to get back down to the lower
bands, everything went haywire and has not been right since.

I ended up with voltages of 18mV at 4MHz and below. L30 became
unresponsive. Voltages were similarly low up into about 10MHz. Then,
above that, voltages moved up, and became very high, around 7.95, and
again unresponsive to adjustments of L30. I could fiddle with the radio
(band switching, powering off, then powering back on), and at times get
back to the original readings, but I could never get the voltage down
to 7.5V or below. In other words,  the radio is acting very strangely.
As an aside, the band switch seems to operating incorrectly in the
lower bands (below 10MHz), often not switching to the lower bands at
all, sometime just not switching the the proper band (ie. the next
lower band). I don't know if this is a cause or and effect of the
voltage problem. I am very suspicious of one or more relays because of
the odd band switching. And I'll just "fess up" here and admit that I
did (inadvertently) clip the leads on several relays AFTER soldering
them; the manual says not to trim the leads. Did I mess up relays and
cause the voltage problem? During the Alignment and Test: Part I, the
relays seemed to work fine, but that was before I clipped any leads.

I've check all values of components in and around L30, as directed in
the manual. I've reheated solder joints and looked for soldering
problems. I've verified the turns and connections on T5. So I'm
basically at a loss.

I appreciate your suggestions.

Mike/NR7F

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[Don Wilhelm-3]

Mike,

Since you suspect a relay problem, the easiest thing to do is check them,
and actually that is mot difficult - the first page of the K2 schematic
section has a chart of 'which relay is set/reset' for each band, and the
schematic itself shows the relays in the reset condition.  These are
latching relays, so switch to the band you wish to check and then turn power
off the K2.  The position of the relay points can easily be determined with
an ohmmeter.  The pins are numbered, and pin 1 is the round solder pad
(others are square).

Actually the more likely thing would be that you have an unsoldered
connection somewhere in the PLL/VFO area (it was making contact before, but
a bit of a bump changed that). Look at the K2 schematic to identify the
components in those circuits, then check each of them physically.

The other thing to check carefully is the thermistor board - it is quite
easy to create a solder bridge on this board.  You may have to remove it to
check.

73,
Don W3FPR

> -----Original Message-----
>
> Hello all, and thanks to those who responded to my recent message
> regarding the PLL reference oscillator test.
>
> I no sooner resolved that issue than I ran into a more puzzling issue
> during the VCO alignment. On the initial test, I had reasonable
> voltages through the entire band (ranging from 2.066V to 7.95V).
> Several high voltages, but most were well within the range. However,
> when I tapped the band switch button to get back down to the lower
> bands, everything went haywire and has not been right since.
>
> I ended up with voltages of 18mV at 4MHz and below. L30 became
> unresponsive. Voltages were similarly low up into about 10MHz. Then,
> above that, voltages moved up, and became very high, around 7.95, and
> again unresponsive to adjustments of L30. I could fiddle with the radio
> (band switching, powering off, then powering back on), and at times get
> back to the original readings, but I could never get the voltage down
> to 7.5V or below. In other words,  the radio is acting very strangely.
> As an aside, the band switch seems to operating incorrectly in the
> lower bands (below 10MHz), often not switching to the lower bands at
> all, sometime just not switching the the proper band (ie. the next
> lower band). I don't know if this is a cause or and effect of the
> voltage problem. I am very suspicious of one or more relays because of
> the odd band switching. And I'll just "fess up" here and admit that I
> did (inadvertently) clip the leads on several relays AFTER soldering
> them; the manual says not to trim the leads. Did I mess up relays and
> cause the voltage problem? During the Alignment and Test: Part I, the
> relays seemed to work fine, but that was before I clipped any leads.
>
> I've check all values of components in and around L30, as directed in
> the manual. I've reheated solder joints and looked for soldering
> problems. I've verified the turns and connections on T5. So I'm
> basically at a loss.
>
> I appreciate your suggestions.
>
> Mike/NR7F
>
>

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