[Elecraft] K2 - KAT2 receive 4.7v voltage out on U4 pin 1 and 7

[Don Wilhelm]

Chris,

If I understand you correctly, you have a very low voltage on U4 pin 3 
during receive, and the 4.6 volts on pin 1 did not decrease after you 
transmitted. (pin 1 and pin 2 should be at the same voltage).

I believe what is happening is that the charge on U4 pin 1 had no where 
to bleed off, so it stayed at greater than 4 volts.
If that is the case, I do not think there is any problem - that behavior 
will cease when you install R6..

U4 is wired as an op amp buffer.  Normally the voltage on pins 1 and 2 
will be the same as the voltage on pin 3.

73,
Don W3FPR

On 7/14/2013 11:05 PM, ChrisM wrote:
> I have finished building the KAT2 got the null to 001 and then checked the
> voltage at pin 1 at U4 which read at 0 on receive then went into tune at 5W
> and P1, U4 read about 4.6v. When I went back to receive the voltage at P1
> and 7, U4 was 4.7v. Checked voltages on receive and P8, U4 read 6.06v and P3
> read 0.01v to 0.02v, P4,5, and 6 of course at 0.00v. P5 of U1 and R1 center
> also read between .01 and .02v. Assuming U4 was bad I replaced U4 with
> another LM358 (not 100% sure if good, never used before.) and now have 4.8v
> on 1 and 7 with all other voltages the same as before. Could U4 be good and
> am I missing something or do I need to buy a new LM358 that I know is good
> (have another LM358 how can I check it before I install it?)? Any help or
> Ideas would be appreciated.
>
> The K2 itself passed all tests once I got a good Dummy load. Just been
> listening and limited to 20m to 10m due to size of my hobby room. Have yet
> to make any contacts as I still have to get a mic or learn CW.
>
> Thanks,
>      Chris KD0WDK
>