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

[C. J. Hawley]

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 

---- Original message ---- 
>Date: Tue, 20 Oct 2009 23:40:36 -0400 
>From: Don Wilhelm <don at w3fpr.com>   
>Subject: Re: [Elecraft] Just built K2 and finals seem to be oscillating...   
>To: c-hawley at illinois.edu 
> 
>Chuck, 
> 
>I have given you about all the info I can until I can refer to the 
>schematics and make a guess about where the 450 Hz might be coming 
>from.  I am currently thinking that there should be no DC at W6, but I 
>could be wrong on that. 
> 
>As far as the sidetone source - yes, with firmware 2.04r, you must add 
>the sidetone source wiring change to obtain sidetone for all control 
>boards below SN 3000 - whether or not you have the KIO2 or KPA100 
>installed.  The statements in the firmware document override since they 
>are dated later than the A to B upgrade or the KIO2 or KPA100 
>instructions.  Version 2.04r firmware eliminated the U6-25 sidetone 
>output option and will save a lot of support effort in the future. 
> 
>73, 
>Don W3FPR 
> 
> 
>C. J. Hawley wrote: 
>> Thanks. I went back and re-read his note and he did mention K2-T2 as well. Then I went to the newest manual and K2-T1 and K2-T2 are now shown wound the way he did them for me. All reverse from the original manual. So that's not an issue I see. 
>> I still don't have a solution though. I checked 8T, 8R, measured all the D1 thru D4 diodes, took out the 160M board and shorted J14 to restore W1, resistance checked to see that all the chokes, etc. are installed in the T-R switch area. 
>> 
>> After more careful checking with the power knob all the way down, I get about 3 vpp at W6 riding on 8 vdc. I get very small voltage at BPF on transmit and as well on Xmixer and buffer. 40 vpp with 8 vdc on D3-D4 cathodes, 60 vpp at 0 vdc on W1 (with 160 removed), and the same 60 vpp at 0 vdc on the output ant jack. Fundamental freq is about 450KHz. 
>> 
>> I also read the instructions for rev 2.04 firmware which said to revise the A board according to KIO2 mod details for sidetone, but I kept going back to rev B mod page where it said I didn't have to if I didn't have KIO2. The issue is that the new rev 2.04 firmware does not have the option to use U6-25. It only allows U8-4. Once I cut the trace, etc. all works well for the sidetone. 
>> 
>> Beats me... 
>> 
>> Chuck, KE9UW 
>> 
>> ---- Original message ---- 
>>    
>>> Date: Tue, 20 Oct 2009 17:56:27 -0400 
>>> From: Don Wilhelm <w3fpr at embarqmail.com>   
>>> Subject: Re: [Elecraft] Just built K2 and finals seem to be oscillating...   
>>> To: c-hawley at illinois.edu 
>>> Cc: elecraft <elecraft at mailman.qth.net> 
>>> 
>>> Chuck, 
>>> 
>>> The winding sense that The Toroid Guy was referring to is T1 and T2 for 
>>> the KSB2 board, not the base K2. 
>>> The winding sense on those transformers will make no difference. 
>>> 
>>> From your previous post, I see you have an oscillation that appears as 
>>> far back as W6.  That can be a problem muh earlier in the transmit 
>>> chain, like at the TX mixer or the Transmit buffer.  Check the RF levels 
>>> of the VFO and BFO at the transmit mixer (see the Receive and Transmit 
>>> Signal Tracing sections in the back of the manual for the normal levels. 
>>> Also check the frequency at TP2 and TP1 to be certain they are correct - 
>>> the VFO frequencies for each band are listed on the Schematic Key page. 
>>> 
>>> 73, 
>>> Don W3FPR