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

[David Broger]

Hi Michael
Thanks for the quick respons.
When I "tune up" the frequency by putting a finger on t5, followings
happend:
 - as long the frequency is rising the voltage at R30 is 8.1 volts
 - when frequency arrives at 9.1MHz the voltage at r30 goes to 4volts. The
frequency goes down to 8.9MHz
when I make the finger wet, the frequency rises much faster and the voltage
at r30 changes faster too.
I tried to adjust l30. It was possible to adjust it to 6 volts (with the
finger at t5). When I removed the finger, the voltage goes up to 8.1 volts.

Is it possible that I increase the inductivity with the finger???
Can it be that the core has a invisible crack (falling down on the floor)?

C96 is "105" -> 1000'000pF -> 1uF -> ok

The voltage at r9 is at the front-connector 8.1 volts and at the
backside-connector 1.6 volts. By putting a finger to t5 the voltage at r9
(backside-connector) rises linear withe the frequency. At 8.9MHz the voltage
is 2 volts. When die voltage is rising there ist a quiet sound in the DMM.
It starts at fow frequency and stops at high frequency. At 1.6 volts and 2
volts is no sound.

I put the finger between the connectors 2 and 4 at t5.
The serial-number is 3613.
I have only a DMM.

Next intresting point: I measured the voltage between ground and connector 4
of t5 - its 0.07 volts (touching t5 has no effect) but the frequency goes up
to 8.8 MHz!! When I touched the connector 4 with a insulator or metal-piece
the frequency goes not to 8.8 MHz.

73 de David


-----Urspr�ngliche Nachricht-----
Von: Masleid, Michael A. [mailto:Michael.Masleid@ispat.com]
Gesendet: Dienstag, 19. August 2003 18:06
An: David Broger
Betreff: RE: [Elecraft] K2 - VCO-Test (Alignment an d Test, Part II)


Hello David,

Seems like T5 must be good.

>I made a new toroid - exactly according the manual - with good
>solderpoints - all exact - but no success - frustration becomes larger!!
>What's the problem?? I can't see a problem at t5. Putting a finger between
2
>and 4 (at t5) the frequency moves to  8.6 MHz (it takes about some seconds)
>but I can't see changing in resistance at t5.

You should be seeing a voltage change at R30 as this is happening.  Do you?

The time delay is due to C96 mostly.  This is 1uF, right?

Look at the voltage on R9 on the collector side of Q16.  Does this change
suddenly when you get your finger by T5?  (Oscillator level control)

I think perhaps T5 is not oscillating, and adding a finger may be increasing
feedback around C68 just enough.  Of course, I don't see where TP1 is
getting
the 1 MHz signal, but feed back circuits do weird things sometimes.

If Q18 isn't kicking into oscillating at 8 MHz, check out components around
Q18 also.  There's some things in troubleshooting that might also help.

This is getting interesting.
Exactly where are you putting your finger?

I don't have too many quick ideas right now.  I'll take mine (#3430) apart
and see
what it looks like around T5.  But that will be 10 hours from now.
What serial number is your K2?  What type of test equipment do you have
available?

73 de Masleid AB9GV