[Elecraft] K2 trouble shooting

Wed Nov 4 09:53:31 EST 2009

Mike,

Yes, it sounds like you have it adequately analyzed and I do agree with 
your conclusions.  FP U3 has a bad pin 14 output and the MCU input for 
ENC A also has a problem and is dragging the signal down.

73,
Don W3FPR

Mike-WE0H wrote:
> Hi Don,
>
> OK, I can see those signals on pin 6 & 16 easily. Pin 14 is dead. It 
> stays low. I am using DC coupling. ENC-A is only going to 2v and ENC-B 
> goes to 5v. Both those data lines show data when the encoder is spun in 
> either direction. Both lines will either rest at zero or a high state. 
> But, ENC-A high is 2v not 5v. ENC-B high is 5v. Something is not right 
> with ENC-A. If I pull the jumper wire from the encoder's ENC-A line and 
> put the scope on the encoder's ENC-A terminal, I now get the 5v p-p 
> signal that I would expect out of the encoder. So with that said, the 
> MCU is not letting the ENC-A data line swing from 0-5v. It only allows a 
> 0-2v swing which is not enough. Would you agree the MCU is faulty & the 
> U3 IC? Having two IC's giving troubles is rare but this radio suffered 
> from severe spikes on the 14v line which shorted a electrolytic cap and 
> one final transistor.
>
> BTW, I am copying this to the Elecraft reflector so it is in the 
> database for someone else down the road. This is definitely a strange 
> problem with this radio. I think we are getting closer to the solution.
>
> Mike
> WE0H
>
>
>
> Don Wilhelm wrote:
>   
>> Mike,
>>
>> Do you have the 'scope vertical amp set to DC?  This is logic level 
>> switching and the DC levels are significant, not the peak to peak 
>> variation.  Yes, the levels must be above or below the switching 
>> thresholds.
>> On the /ENC RD line, compare it to the levels at FP U3 pins 6 and/or 
>> 16 - it should be similar.
>> To really tell the whole story, one would have to use 3 probes on the 
>> 'scope - trigger on the /ENC RD signal going low and observe the state 
>> of the ENC A and ENC B signals at that time.
>>
>> Elecraft does repairs, but only on complete kits.  If this is the 
>> route you need to go, contact sales at elecraft.com for further 
>> information and obtain an RSA number with instructions for packing and 
>> where to send it.
>>
>> 73,
>> Don W3FPR
>>
>> Mike-WE0H wrote:
>>     
>>> Hi Don,
>>>
>>> OK, on that line which is pin 14 on U3, there is only a couple mv but 
>>> no pulses. The state of that line never changes. The other strange 
>>> thing is the ENC-A data level only being 2v p-p verses ENC-B which is 
>>> a full 5v p-p signal. Shouldn't both ENC data lines be a full 5v p-p 
>>> TTL signal?
>>>
>>> Worst case, does Elecraft take in repairs direct? I could send in 
>>> both display boards if that is the case. I sure wish I had test 
>>> boards to swap in, to verify which board is causing the issues.
>>>
>>> I received the final amp rebuilding components the other day but I 
>>> will wait to install them until after this dead VFO issue is repaired.
>>>
>>> Mike
>>> WE0H
>>>
>>>
>>>
>>> Don Wilhelm wrote:
>>>  
>>>       
>>>> Mike,
>>>>
>>>> Other than the wiring paths for ENC A and ENC B signals through the 
>>>> connectors and to CB U6 pins 8 and 16,
>>>> there is nothing else for these two signals.  However, for the 
>>>> encoder to be read, the /ENC RD signal must be at a low level and 
>>>> that signal is generated from FP U3 pin 14.  Look for low going 
>>>> pulses with your scope.  If they are not present, FP U3 may be at 
>>>> fault.
>>>>
>>>> 73,
>>>> Don W3FPR
>>>>
>>>>
>>>> Mike-WE0H wrote:
>>>>    
>>>>         
>>>>> Hi Don,
>>>>>
>>>>> Ref K2 #6698:
>>>>>
>>>>> I tried a new encoder but it did nothing different than the 
>>>>> original encoder. Tonight I see that ENC-A is only 2v p-p while 
>>>>> ENC-B is 5v p-p. This is measured right on the encoder terminals 
>>>>> and on the U6 MCU chip. I don't see any resistor network pull ups 
>>>>> on these lines. Do you think the MCU could have gotten hurt with 
>>>>> the spike on the 14v VCC line that shorted the one final and that 
>>>>> VCC filter cap? I see data on both ENC lines when I spin the 
>>>>> encoder. The Encoder VCC is a solid 5.0vdc. All other functions 
>>>>> work on this radio except anything where I need to turn the encoder 
>>>>> to access something in a menu or change anything. The radio 
>>>>> receives fine on whatever the display freq is and transmits fine on 
>>>>> the same freq on all bands. I just can't change any VFO digit other 
>>>>> than the far right digit, or if I spin the encoder shaft left & 
>>>>> right, it will slowly increase the displayed freq but not go down.
>>>>>
>>>>> Mike
>>>>> WE0H
>>>>>           
>
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