[Elecraft] [K2] No signal at TP1 during Alignment and Test Part 2

[Robert Forster]

Hi Don and Group,

I got a bit of time to troubleshoot this evening.

I do have a good signal at TP3 so I am ignoring the PLL and U4.

I did the DC measurements at Q18 and found some issues.

the gate shows as a negative polarity but at -.001 volts
Source is .08
Drain is at 6.8

This should lead me to suspect T5 correct?
the soldering on the underside of the board for T5 looks ok (no ring for
these points but the topside of the board looks rough!  I used the USB
microscope and took some photos.
Here: https://flic.kr/s/aHsm2aNdeG

 I'm thinking that after the VHF contest I should remove T5 and check the
windings and re strip the ends and retin.  Does this sound like an
apropriate course of action?

Oh and just for the hell of it I bypassed C60 with no effect either.

Thanks again for all your help!

73,
Robert
AD0TA

On Wed, Jun 7, 2017 at 6:33 AM, Don Wilhelm <donwilh at embarqmail.com> wrote:

> Robert,
>
> Do you have a good signal at TP3?  If so, ignore the PLL Reference
> oscillator and U4 for now.
>
> You need to get the VFO operating before doing anything else.
> Do the DC measurements a Q18.  If you do not have a negative voltage at
> the gate, it is not oscillating.
>
> T5 is the most likely problem with the VFO.  Make certain it is wound
> correctly and the leads are well stripped and tinned.  If you see a ring
> around the lead (on the solder side), that lead was not adequately stripped
> and tinned.  Both windings must be wound in the same direction.
>
> If all the above is correct, put a temporary jumper across C60 to disable
> the VFO ALC circuit.  If it oscillates with the jumper in place, but not
> without it, replace Q17.  If that still does not correct it, try replacing
> Q16.  Be certain D11 is oriented correctly.
>
> Ignore the voltages on U4 pins 5, 6, and 7 - those are digital signals,
> and the manual lists the voltage for the active signal, not what you would
> typically measure with a DMM.  If you look at them with a 'scope you can
> see pulses on those lines, and that should be sufficient for proper
> operation.
>
> RFC 15 also needs to be ignored until after you get the VFO operating.
> Once you get a VFO signal at TP1, then you can investigate the operation of
> U4.
>
> 73,
> Don W3FPR
>
>
> On 6/6/2017 9:47 PM, Robert Forster wrote:
>
>> Hello to the group!
>>
>> I'm afraid I need to lean on your collective K2 troubleshooting expertise.
>> After a long break I have finally made it to the Alignment and Test Part 2
>> of my build.  Everything was going OK until I got to the VCO Test.  I have
>> no signal at TP1.  I have tested this with the built in counter as well as
>> an external counter.  I have gone through some of the troubleshooting I
>> could find online:
>>
>> The orientation of D13 and D8 look good
>>
>> I have checked the soldering at relays K13, K14 and K15 and the value of
>> C72.
>>
>> I have checked the varactors at D21 through D26 and they are oriented
>> properly I am nearly certain they are all the correct type
>>
>> I tested RFC15 in the circuit and could not get any continuity through it.
>> When I pulled it out of the circuit it tested fine so I put it back in.
>> I'm sure this is something basic I just dont understand.
>>
>> I know there is some more testing I can do with Q17 and Q18 (I did check
>> that they are the right type and orientation I also check all the
>> component
>> values around Q18) Lets set that aside for just a second though...
>>
>> Here is where I think it gets a little weird.  Looking at the schematic I
>> followed it back to U4.  When I compared the voltage table to what i was
>> actually seeing on U4 I think I may have found my problem.  According to
>> the table pin 7 should have 0 Volts but i'm showing 4.8!  It also shows
>> that pin 13 should have 4 volts but I'm showing 0.  All other pins are
>> normal and match the chart.
>>
>> Following Pin 7 of U4 back to Pin 1 of U5 I see the same 4.8 volts.
>> This is supposed to be a clock line so I'm confused where this sort of
>> voltage would be comming from.
>>
>> I'm still new to alot of this and this is by far the most complex kit I've
>> taken on so any and all help will be appreciated!
>>
>> Thanks and 73,
>> Robert
>> AD0TA
>>
>>
>>
>>


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