[Elecraft] K3 Voltmeter calibration ...

Tue Nov 24 21:38:54 EST 2015

On 11/24/2015 8:17 PM, Walter Underwood wrote:
> The measured voltage is what the rig is really seeing, after the
> protection.

That *is not the case* I've checked the voltage on the KPA3 and, again,
the Voltage display is approximately 0.2 Volts *lower* than measured at
"12PA" - the output of CB1.

Again, *HOW DOES ONE CALIBRATE THE VOLTAGE DISPLAY?*

CONFIG: ADC REF matches the voltage measured at pin 2 of the ACC jack
with nothing connected to the +12V Out.  However, the Voltage display
does not match the voltage at either the APP or +12PA.  That the
"meter" is not accurate at *either of the two* most important points
- the two points that have the greatest impact on performance - is not
acceptable.

*HOW DOES ONE CALIBRATE THE VOLTAGE DISPLAY?*

73,

   ... Joe, W4TV

On 11/24/2015 8:17 PM, Walter Underwood wrote:
> The measured voltage is what the rig is really seeing, after the protection. If you don’t want that, you need to put your own voltmeter outside the rig.
>
> A 0.2V difference isn’t calibration, this is you disagreeing with an Elecraft design decision.
>
> wunder
> K6WRU
> Walter Underwood
> CM87wj
> http://observer.wunderwood.org/ (my blog)
>
>> On Nov 24, 2015, at 4:55 PM, Joe Subich, W4TV <lists at subich.com> wrote:
>>
>>
>> As I responded to to Mark off list, I know the REF ADC calibration and
>> had already performed it *before* asking for assistance here.  The
>> voltage display was off by more than 0.5 V prior to performing REF ADC.
>> The remaining the error is still unacceptably high at more than 0.2 Volts when a simple DVM has significantly greater accuracy.
>>
>> I *still* seem to recall a calibration procedure for voltage similar to
>> that for FP, PA, etc. during the initial assembly and test of this K3.
>> It seems inconceivable that such a calibration process would not be
>> present since the "12V" sense point follows at least D6 if not D6, Q2,
>> RFC40 and R36 which in total would introduce a substantial fraction of
>> a volt offset from the voltage at the APP and provided to the KPA3.
>>
>> 73,
>>
>>   ... Joe, W4TV
>>
>>
>> On 11/24/2015 6:32 PM, Mark E. Musick wrote:
>>> I sent Joe K3 manual REV D6 from early in 2010.
>>> On page 53 of that manual it has the following description for ADC REF and
>>> how to calibrate it.
>>>
>>> ADC REF
>>>
>>> Allows calibration of the voltage reference used by the K3 to measure and
>>> display
>>> certain values, such as the rig's supply voltage. (Optional.) First,
>>> disconnect
>>> anything attached to the ACC jack. Next, locate the ADC REF menu entry. It
>>> will
>>> initially show 5.00 volts as the reference voltage. Using a DMM set to DC
>>> volts,
>>> measure the actual voltage at pin 2 of the ACC jack. This must be done while
>>> the
>>> ADC REF parameter is being displayed. (Note: The (-) probe of the DMM
>>> should go to the K3's chassis ground, e.g. at the GROUND lug.) Finally, use
>>> VFO
>>> A to set the ADC REF menu parameter to what you measured at pin 2.
>>>
>>> So you need to set ADC REF to the voltage on pin 2 of the ACC jack. NOT what
>>> is at the APP connection on the RF board.
>>>
>>> 73,
>>>
>>> Mark Musick, WB9CIF
>>>
>>> -----Original Message-----
>>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Brian
>>> & Cyndi
>>> Sent: Tuesday, November 24, 2015 11:19 PM
>>> To: elecraft at mailman.qth.net
>>> Subject: Re: [Elecraft] K3 Voltmeter calibration ...
>>>
>>> And the info below is what I found in Fred Cady's book on the K3. There is
>>> no other "calibration" for voltage in that book.
>>>
>>> Until Don Wilhelm or Wayne Burdick chimes in,  I suspect there may not be
>>> any other adjustment available.
>>>
>>> 73,
>>> Brian, W6FVI
>>>
>>> On 11/24/2015 1:49 PM, Joe Subich, W4TV wrote:
>>>>
>>>> I've already set ADC REF as documented in the manual.  The Voltage is
>>>> still off.  There should be a procedure to set the voltage as there
>>>> was when I assembled this K3 (s/n 1450) several years ago.
>>>> Unfortunately, I can no longer find it in the current Owner's Manual
>>>> or Assembly Manual.
>>>>
>>>> 73,
>>>>
>>>>    ... Joe, W4TV
>>>>
>>>>
>>>> On 11/24/2015 4:01 PM, Brian & Cyndi wrote:
>>>>> Joe, if you just want to make the K3's voltmeter match your "known good"
>>>>> reference meter, you need to adjust the "ADC REF" value.
>>>>>
>>>>> Go into the CONFIG menu, set Tech mode "On", then go to the "ADC REF"
>>>>> setting.  Note what it is before changing anything, in case this
>>>>> adjustment affects anything else adversely.  Adjust the ADC REF value
>>>>> to cause the voltmeter display to read the value you want. You will
>>>>> need to go in and out of the menu display to see the results (kinda
>>> clumsy).
>>>>>
>>>>> Again, this adjustment may affect other measurements, so an accurate
>>>>> K3 voltmeter may not be that important after all.
>>>>>
>>>>> 73,
>>>>> Brian, W6FVI
>>>>>
>>>>> On 11/24/2015 9:32 AM, Joe Subich, W4TV wrote:
>>>>>>
>>>>>> It matters not if there is a series diode.  The Voltmeter should be
>>>>>> calibrated to the input power.  I remember that being the case when
>>>>>> I assembled my first K3.
>>>>>>
>>>>>> 73,
>>>>>>
>>>>>>     ... Joe, W4TV
>>>>>>
>>>>>>
>>>>>> On 11/24/2015 11:02 AM, Michael Blake wrote:
>>>>>>> Joe, is there not at least one diode junction or solid state switch
>>>>>>> in series with the input power inside the K3?
>>>>>>>
>>>>>>> Michael Blake - K9JRI
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> On Nov 24, 2015, at 10:06 AM, Joe Subich, W4TV <lists at subich.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> OK, I'm sure I am overlooking something simple but I can not find
>>>>>>>> (or remember) how to calibrate the voltage display in the K3.
>>>>>>>>
>>>>>>>> I had to repair one of my Astron RS-35A power supplies for the
>>>>>>>> first time in 30 years (one of the diodes shorted) and when I put
>>>>>>>> it back on line I decided to double check the K3 Volts display
>>>>>>>> against the actual output of the supply.  The K3 is reading about
>>>>>>>> 0.2V less than the supply voltage.
>>>>>>>>
>>>>>>>> I've been over both the K3 Owner's Manual and the K3 Assembly
>>>>>>>> Instructions but can't find any reference to calibrating the
>>>>>>>> voltage display.
>>>>>>>>
>>>>>>>> 73,
>>>>>>>>
>>>>>>>>     ... Joe, W4TV
>>>>>>>>
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