[Elecraft] K2/100 overheating?

[Don Wilhelm]

Ken,

That bias setting is correct.  The current draw seems a bit high to me, 
but may be OK - I do not have typical measurement data.

One more check - make sure that Q6 and Q7 are oriented properly. They 
appear at first glance to have 2 flat sides, but the "round side" has 
chamfered edges.  If those transistors are oriented backwards, they will 
cause the KPA100 to oscillate in the 800 to 900 kHz range.

How hot is your definition of hot?  There will be heat generated. If you 
can hold your hand on the heatsink, it may not be too hot.
The temperature rise should not be much at powers below 20 watts, so if 
yours gets hot at those power levels, there is a problem to be found.

You might want to check the diode voltages as well - both in transmit 
and receive and at power levels below and above 11 watts.  In other 
words, check everything listed in the diode voltage chart.

I just checked the fan direction on my older KPA100 - mine pulls air 
in.  It really does not matter much for cooling purposes in the KPA100.  
The fans were changed about a year ago (availability problem, not design 
change).
The newer fans may not start on the Hi-Lo setting.  You can experiment 
with resistors in parallel with R31.  I would suggest starting with 1000 
ohms and working downward in resistance until the fan starts reliably on 
the Low setting (Hi-Lo starts out low and goes to high when the 
temperature rises).  1/4 watt resistors will be OK unless the value 
necessary goes below 470 ohms, then you should use 1/2 watt.

Make certain the CAL TPA setting in the menu is correct.  The actual 
setting follows the KPA100 temperature, so let it cool for at least 1/2 
hour and set it to the ambient temperature in degC. That will control 
when the fan goes to low and when it goes to high.

73,
Don W3FPR

On 5/23/2017 3:17 PM, N4KS wrote:
> My bias current settings are:
> 275 mA (power knob set fully CCW)
> 475 mA (power knob set to 11 watts)
> Target 875 mA total (with the 400 mA added per the instructions) In CW 
> test mode, I set bias control R6 to show a reading of 875 mA
>
> Current draw:
> 12W = 6.6A
> 40W = 10.0A (note: peaks at 14W then steps down to 12W)
> 120W with Power set full CW
>
> Checked all of the diodes for proper orientation.
>
> Fan is orientated correctly with label out. my fan pulls the air OUT. 
> There seems to be some confusion regarding the direction of air 
> flow. Others advised it should be pushing air in. With the fan setting 
> in "normal" mode, it goes directly to high speed when it kicks in. I 
> should think it would go to low speed first and then step up to high 
> speed if the temperature increases.
>
> Balanced and calibrated the wattmeter.
>
> I checked Q1 Q2 Q3 Q4 DC voltages in RX and TX. All are good according 
> to the Voltage Chart provided in the manual.
>
> I had to order a new Fan, because of a mistake I made. It should be 
> here by the end of the week. I will provide temperature data when it 
> is reinstalled.
>
> 73, Ken N4KS
> k2/100
>
> --------------------------------------------
> On Fri, 5/19/17, Don Wilhelm <donwilh at embarqmail.com 
> <mailto:donwilh at embarqmail.com>> wrote:
>
> Subject: Re: [Elecraft] K2/100 overheating?
> To: "N4KS" <stuberkenneth at yahoo.com <mailto:stuberkenneth at yahoo.com>>, 
> "elecraft at mailman.qth.net <mailto:elecraft at mailman.qth.net>" 
> <elecraft at mailman.qth.net <mailto:elecraft at mailman.qth.net>>
> Date: Friday, May 19, 2017, 6:02 PM
>
> Ken,
>
> Did you set the bias properly?  What is the
> current draw at 12 watts?
> Did you properly
> balance and calibrate the wattmeter?
> Are all
> the diodes oriented properly?  Check against the parts
> layout
> near the back of the manual.
>
> Make certain the fan is
> mounted with the label out and that the red wire
> is in the +hole and the black one in the
> -hole.
> The fan should exhaust the hot air.
> Cooler air flows in at the front of
> the
> heatsink.
>
> 73,
> Don W3FPR
>
> On
> 5/19/2017 8:01 AM, N4KS via Elecraft wrote:
> >  I recently added the KPA100 to my K2.
> The heat sink gets VERY hot at any power level above 11
> watts (that's when the amp kicks in). The fan is running
> at high speed and pulling air OUT of the box. Just wondering
> if this is normal.