[Elecraft] Re: PA HOT

[Dominik Bugmann]

Joe, Rich,

I have/had the same issue here and I posted the findings a few weeks ago on
this reflector
http://mailman.qth.net/pipermail/elecraft/2003-April/053270.html.
What I figured out so far is:
The temperature meter is Q3 and mounted right next to Q1 and Q2. The voltage
drop from B to E is roughly 0.6V and varies over temperature. Fortunately
this effect is very limear (over a high temp range) and much better compared
to a PTC or NTC. Unfortunately the change is only a few mV/C. As you can see
on the page 61 in the manual Q3 is directly connected to U1/PIC16C72 where
they measure the voltage of Q3. To measure a very low level (0.6V) directly
with an A/D converter is not an easy task and I assume that the reference
level within the MCU (U1) is also temperature dependant. When I switch on my
KPA100 I read 8C which goes to 20C within a few minutes. Q3, U1, ..the whole
KPA100 heats up a bit. Nevermind this is not a big issue for KPA100.
Unfortunately there is a softwarebug which occurs as soon as the reading is
below 0C. One would expect a negative number but it is represented as e.g.
255C (underflow of an 8 Bit counter). The controll software for the fan and
"Hot PA" only looks at this number (e.g. 255C) and concludes it must be hot
out there. At least this is my understanding of the whole issue.
My workaround so far: Check the tPA reading of the KPA100 and (re-)adjust if
needed.

73 de Dominik, HB9CZF


>Ditto on what Joe has said. I had my fan on continuously and I check CAL
tPa
>and temp wall 200C. Reset it and no problem.
>Rich
>KQ9L
>
>On 5/13/03 7:04 AM, "Joe Squarzini" <k4aa@verizon.net> wrote:
>
>> Carter, I had the same problem. I found that the PA Temp setting had
>> drifted inexplicably to 256 deg. I reset the parameter to room temp and
so
>> far it has not happened again. I suspect RFI. No proof however. My K2/100
>> is mounted in a separate EC2 enclosure along with the KAT100.   Joe
>>
>> Joe Squarzini, Jr.
>> K4AA
>>