[Elecraft] K2 BFO issues

[Don Wilhelm]

Anthony,

If you are getting 7 volts onto R98, there is no need to look into the 
U10 circuits.
Check the values and soldering in other parts of the RF Board BFO and 
Q24 area.
Is D36 installed properly using pins 2 and 3 on the SMT board with the 
#2 lead in the hole of the silkscreen with the banded end?

73,
Don W3FPR

On 5/30/2017 11:26 AM, Anthony Clare wrote:
> Don:
>
> I just looked at the schematic. I do remember checking the voltage at R98 now
> that I look at it. I do recall getting over 7 volts in and somewhere around
> 5.8 give or take at the drain of Q24.
>
> I never thought to look at U10 or associated circuitry. I will do that as soon
> as I get home.
>
> Thanks,
> Anthony
> n3kcb
>
> ------ Original Message ------
> Received: Tue, 30 May 2017 10:14:48 AM EDT
> From: Don Wilhelm <donwilh at embarqmail.com>
> To: Anthony Clare <n3kcb at usa.net>, elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K2 BFO issues
>
> Anthony,
>
> If you do not find more than 7 volts at the end of R98 that is furthest
> away from Q24, then look at the U10A/Q8 circuit on the Control Board.
> Check the associated components and their soldering.  That is more
> likely to be the problem than the active devices.
>
> 73,
> Don W3FPR
>
> On 5/30/2017 9:28 AM, Anthony Clare wrote:
>> Hello:
>>
>> I am not at home to try, so I will have to check R98 later. I remember
> fitting
>> the encoder and it was definitely a tight fit. I used a dremel sanding drum
> to
>> almost completely flatten the pins in the affected area on the encoder
> board
>> and control board. Then I reflowed all the connections that I flattened and
>> placed fiberglass tape over the encoder board. Once I did this, I could
> look
>> between the boards and see no physical contact.
>>
>> I will separate the control and front panel boards and see what happens when
> I
>> get home.
>>
>> Thanks,
>> Anthony
>> n3kcb
>>
>> ------ Original Message ------
>> Received: Tue, 30 May 2017 08:51:03 AM EDT
>> From: Don Wilhelm <donwilh at embarqmail.com>
>> To: Anthony Clare <n3kcb at usa.net>, elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] K2 BFO issues
>>
>> Anthony,
>>
>> When you put the K2 into CAL FCTR mode, what is the voltage at the ends
>> of R98 (on the bottom of the board).  I am interested only in the
>> highest voltage.
>>
>> With the new K2s (those using the new encoder board), many strange
>> problems are caused by contact of the encoder board with the Control Board.
>> You must flush trim the leads on the encoder board - and I mean almost
>> right down to the board level.
>> Also you must flush trim the back of the Control Board in the area that
>> could come in contact with the encoder board.
>> Make sure the rubber bumper pads are in place at the top corners of the
>> Front Panel Board.
>>
>> As a test, remove the 2 screws that secure the Control Board to the
>> Front Panel and tilt the top of the Control Board to the rear.  If
>> things then behave normally, you can be certain that contact between the
>> encoder board and the Control Board is causing the problem.
>>
>> 73,
>> Don W3FPR
>>
>> On 5/30/2017 8:07 AM, Anthony Clare wrote:
>>> Hello:
>>>
>>> Looks like I am not the only one to have this problem. Just finished
>> assembly
>>> phase 2(?) on the K2. It was during the BFO tests that I realized there
> was
>>> not enough signal at the test point for the internal counter. I checked
> for
>>> poor solder, improper varactor diode install, verified that L33 was intact
>> and
>>> not being shorted by the 5 meg resistor, etc. I ran one crystal at a time,
>> but
>>> neither one would provide the proper signal level alone. I even checked
> L33
>> on
>>> the inductance meter and it came out to about 39uH, which seems about
> right.
>> I
>>> assume the inductance meter has some error. The resistor measures out to
>> about
>>> 5 meg.
>>>
>>
>
>
>