[Elecraft] K2 trouble shooting

[Mike-WE0H]

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