http://elecraft.85.s1.nabble.com/Re-K2-trouble-shooting-tp3943308p3946115.html
these two components. Thank you again and lets hope this is the final
answer to this damaged K2. I will post when and what all was required to
> with your conclusions. FP U3 has a bad pin 14 output and the MCU
>
> 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
[hidden email] 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