Stephen,
I recently posted on this topic. It's worth a repeat -- see below.
73,
Wayne
N6KR
* * *
I recently discovered that a 20-amp power supply with poor power-up
characteristics can cause some odd indications on power-up of the
KPA100. These indications have been reported by several customers.
Technical Details
If the power supply voltage has a significant "bounce" when first
turned on, going high and then low before stabilizing, the
microcontroller on the KPA100 may take an invalid sample of the
temperature. This can cause the fan to come on at high speed for about
two minutes initially, even if it's not set for "high" fan mode. If you
transmit during this two minutes, you may see "PA HOT" on the LCD. If
you go into the CAL tPA menu entry, you may briefly see "tPA 255" until
the next temperature sample has been taken. Once the temperature has
been reset (or if you've waited for over 2 minutes before
transmitting), the unit should function normally. This start-up anomaly
will not damage the KPA100 or K2 in any way, and you can continue to
transmit with the KPA100.
What to Do?
If you experience the above symptoms, you can take one of three steps:
1. We've just added some self-defense against "bouncy" power supplies
to the KPA100 firmware (revision 1.10). This version is shipping with
all new KPA100 kits. It can also be ordered from our parts/firmware/mod
kits web page:
http://www.elecraft.com/order_form_parts.htm#fw
or by calling elecraft sales at 831-662-8345.
2. Turn on the K2's power before you turn on power to the KPA100. This
is what I do, and it's why I hadn't noticed the problem before. The
best way to power the K2 separately is to connect a low-current (4A)
backup supply or battery to the K2's DC barrel jack. (Less convenient
would be to run a "Y" cable from the 20-amp supply to the K2's DC
barrel jack, and not connect the KPA100's APP power supply connector
until after powering the K2 up.)
3. If you notice the fan running at high speed at power up, even if
it's set for "nor" or "loHi" mode, you can go into CAL tPA to force the
KPA100 to take a correct reading. It should function normally after
exiting the menu. (Or, you can wait 2 minutes before transmitting.)
73,
Wayne
N6KR
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