AW: HB9RVS: RE: [Fwd: RE: [Elecraft] K2 - VCO-Test (Alignment an d Test, Part II)]

[David Broger]

Hi Gery
Thanks for the infos.

>It is a very good idea to resolder every part in the PLL/VCO section to
>be sure there are no cold solder joints or poor connections.

why not.. maybe not the worsest way....

>Look in the Secondary Menu to be sure the "d19" entry is set to "n", not
>"Y". This is a reserved setting for a future option.

it's ok

>Also make surehere are no diodes installed at D19, D20 for the same reason.

it's ok

Many times I have seen an incorrect value cap installed in the VCO
section. Make sure all of them are identified correctly and are the
correct values. Check for broken or loose leads on all of the caps, and
that all of the VCO relays are installed in the correct direction and
have all 10 leads soldered well.

>Check that the PLL reference oscillator range test at TP3 is OK, as on
>page 57.

The range is ok (12.084MHz - 12.098MHz)

>Make sure the little 100uH RF choke that is installed on the bottom of
>the RF board at U4 pin 16 is not open. It should show less than 10 ohms
>series resistance on an ohmmeter. U4 will partially work even if this
>RFC is open, but there will be stability problems with the output signal
>from U4 pin 13.

It's 8.3 ohms. The contact is ok.

>Also make sure there is 5VDC at U4-16,

it's ok

>and that U8 is not reversed.

it's ok

Check too, for reversed diodes at all of the varactors,
>and at D8, D11, D13, and D18.

all ok

>If Q17 is open or shorted, the DC voltage at T5 pin 3 will be either too
>high or too low (VFO ALC). It is normally about 1-2VDC on all bands, and
>is self-adjusting as you change bands.

normal measured the voltage is 0.85 volts. When I touch t5 I get about 1.2
volts.

>You can bridge C60 or Q17 D to S if you find
>Q17 is open. This will allow the VCO to have a DC return path so it will
>oscillate. But there will then be no VFO ALC until Q17 is replaced with
>a new part.

I replaced c60 with a bridge. And the frequency is stable at 8.9 MHz!! I can
adjust l30 to 6 volts at r30!
I installed c60 and replaced q17 with a new one. I thought the problem will
be solved.... but it's not!!!!! The frequency is down. When I shorten c60
the frequency ist at 8.9MHz and when I take the bridge away the freq goes
down.

I checked the solderpoints at d11,13,8 and 18. Then I swiched on - the
frequency was 8.8 MHz. I thought the problem is solved but the frequency
falls slowly down (about 10 seconds) to 1.7MHz...


>A bad part is rare, but possible. If you eliminate poor connections and
>parts placements errors, you may need to try a new device for Q18 (or
>Q17). There are other J310 transistors in some of the kits you could
>borrow as a test, or email parts@elecraft.com and Scott will send you
>replacement parts.

At the moment I haven't a J310 so I can't change Q18



73 de David