[Elecraft] K2 finals

[Don Wilhelm]

John,

What is the DC voltage at the base of Q7/Q8 during a TUNE?  If it is in 
excess of 0.64 volts, then Q11 and Q13 as well as Q7 and Q8 are toast.  
Order and install the K2PAKIT which includes all those parts.  Q7 and Q8 
are connected in push-pull output, so a failure of one will reflect on 
the other.

I don't know how that would change the behavior of the KIO2, so you may 
have multiple problems in your K2.

If you want to do a test, remove the KAT2 and try working into a 50 ohm 
dummy load.  If you then have good power output, the PA transistors are 
OK and the problem lies with the KAT2,

73,
Don W3FPR

On 8/9/2013 11:39 PM, John Zaruba Jr wrote:
> I was using my new to me K2/10 (S/N 50xx) which has been working flawlessly for the last 2 months when out of the blue I started getting a P LO message from the KAT2. I checked the power out with an external meter and it was about .4 watts in general agreement with the K2 power display. No snap, crackle, or other dramatics, just loss of power. Coincident with the output power failure, the KIO2 stopped working, neither receiving or sending data. Coincidence does not imply causality, so I'm going to treat this as a separate issue.
>
> I started signal tracing per the manual with a DSO scope (Tek TDS-210) and the RMS voltages I read on the scope were nothing like the voltage charts, so I was just looking at voltage gains from the various stages. I removed the KSB2 and installed the cap and 2 jumpers to eliminate that module, with no symptom change.
>
> The one anomaly I think I've found occurred with Q7 & Q8, the voltage at each device's base lead was 3.2 VRMS (as measured by the cyclic RMS setting on the scope), but the collector voltages were around 500 mVRMS. Just to clarify my thinking, I would expect the collector voltage to be significantly higher than the base voltage.
>
> As an additional question, if I have had a final amplifier failure, what might cause both devices to fail, rather than one or the other? Hopefully I can receive some wisdom from the list before I call the factory on Monday to order parts (to make sure I get the correct ones) I'm also thinking I should order new thermal pads and shoulder washers, if new finals are indeed required.
>
>