Re: Cooked K2/PA100 with PSK

Posted by Don Wilhelm-4 on Jun 01, 2010; 10:34pm
URL: http://elecraft.85.s1.nabble.com/Cooked-K2-PA100-with-PSK-tp5128043p5128362.html

Casey,

Since it always transmits at maximum power, that alone may be your only
problem.  Look at it this way - if you had 40 watts requested and it was
putting out maximum power no matter what the power setting, it would be
operating at 100 watts or more and yes, on PSK, the heat sink would get
mighty hot.

The condition is that the K2 microprocessor is not being properly
signaled with the output level (the uP thinks there is no power), so it
ramps up the drive in an attempt to develop more power.  In SSB, the
control is on the KSB2 board which behaves a little differently, so
right now I am not very concerned with the power output level in SSB -
maybe later, but that is to be seen after you get power level control back.

The first thing to check is the condition of KPA100 diodes D16 and D17.  
You can check them in-circuit with your ohmmeter, just as you would
check any diode. low resistance one way, high resistance with the leads
the other way - if they do not measure like that, replace them.

If the diodes are both OK, then there is the possibility that there is a
problem with U5 or U6.  Let me know and I can give you some checks for
those circuits.

BTW, when things cool down (power off for more than two hours), check
the CAL TPA setting, and make certain the fan works at both low and high
speed.  It sounds suspiciously like your fan did not come on at high
speed like it should have.

73,
Don W3FPR


TI2/NA7U wrote:

> I was running my K2/100 at 40W during PSK and the heat sink was too hot to
> touch (ooops!). Now it has the following symptoms of sickness:
>
> - in CW mode key down it generates either 100W or 10W when in high or low
> power mode respectively. In other words, always outputs maximum power.
> - in SSB mode it won't put out more than 20W and only if I drive the audio
> pretty hard. I only do this for a second or two, not trying to make things
> worse =^)
>
> I need advice on how best to organize my triage of the problem, where to
> look first, second, etc. I'm handy with tools, DMM, and at following
> instructions. :)
>
> TIA,
>
> Casey
>  

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