[Elecraft] KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...

[C. J. Hawley]

Good idea...I'm at that stage where I need to check parts and try to isolate. The receiver and all works well.
Thanks, Chuck, KE9UW

---- Original message ----
>Date: Wed, 21 Oct 2009 08:42:52 -0400
>From: Don Wilhelm <w3fpr at embarqmail.com>  
>Subject: Re: [Elecraft] KE8UW Re: Just finished K2 and finals look to be oscillating at 450KHz...  
>To: c-hawley at illinois.edu
>Cc: elecraft <elecraft at mailman.qth.net>
>
>Chuck,
>
>Since you have a 'scope, I would suggest you remove the PA transistors 
>from the picture and see if the oscillation persists.  You can easily 
>de-solder T3 which will remove voltage from the PA collectors.
>If you still have the oscillation at the base of Q7/8 (or at the 
>collector) of Q6, then you can more easily troubleshoot it without fear 
>of damaging the PA transistors.
>Q6 can similarly be taken out of the operating condition by removing a 
>choke or resistor.  I don't have the schematics with me while on 
>vacation, so you will have to find out which one on your own.
>
>73,
>Don W3FPR
>
>C. J. Hawley wrote:
>> Yes the W6 point gets 8 volts either thru the diode D2 or D6 depending on whether in receive or xmit. I think I have an oscillator at Q5-Q6. I am checking all the feedback chokes and capacitors. I may need to unsolder C118 and see if it is infact a capacitor inside the shell and maybe also C120. RFC6 checks ok, R49, R470, etc. 
>> Thanks for the interest and help. 
>>
>> Chuck, KE9UW 
>>   
>>