[Elecraft] KPA100 Low power on the low bands

[Daniel L Brinneman]

Hi,

Take out your KPA100.

Turn the basic K2 on.  If you have the KAT2, put it in the CAL P mode on
ATU menu.   If not hook up your basic K2 RF-board antenna to an external
wattmeter which is hooked up to a good 50 ohm dummy load.  Use an
oscilliscope on AC coupling.   Set your radio to a band of choice, such
as 80m.  With the oscilliscope probe, put ground lead on a ground point,
make sure that your alligator clip has NO WAY of shorting out a component
on either side of the ground point if you were to move your hand.  If it
does, you will definitely short a component out.  With the front of the
K2 facing you, identify the LPF section in the back right-hand corner
near the RF-board antenna.  If you have the 160m option in, you can take
the screw out, take out the module from the pins and lay the board; still
attached to the RX antenna; outside the K2 upside down to the back left. 


To be safe follow this procedure.  Use your RF board schematic (sheet 3
of 4) for these correct test points.
On oscilliscopes' probes there is a hook which can be removed to produce
a point.  
Connect your osciliscope's probe ground to a ground point on the K2. 
Make sure that it will NOT short anything else out while the radio is on.
 The 80m LPF is at the very back of the radio under or behind the 160m
module.  Notice the very left torroid,  place the point of your probe to
the pad for the lead of the very left torroid.  Hold your probe hand
steady and turn on the K2, placing it on 80m.  For all these tests, set
your power out to 1 Watt.  Now press TUNE, notice the internal meter on
your K2 compared to the external meter reading.  If you see Hi Cur, get
out of the TUNE mode.  Don't stay in the TUNE mode too long (5-10
seconds).  Now with the K2 off, move your probe point to the very right
torroid's lead, test the same thing.  You should see that you get a
blurry signal on the very left torroid and a clean signal on the very
right torroid.  

NOW HERE IS THE TEST TO FIND A BAD RELAY THAT IS NOT WORKING IN THE LPF
SECTION.  [With RX set to 80m, then set to TUNE mode, you are looking for
a relay in the LPF that should not be active {meaning no RF on the input
or output on the relay for another band, that is not selected on the RX
display of the K2}, if it is active than that relay(s) needs to be
replaced.  Only 80m should have RF output on its relay and no other
relay.] After doing the tests mentioned above, turn off the K2 and
replace your probe point as discussed above in checking the LPF for the
next band. Turn on your K2, still on 80m RX, go into the TUNE mode and
look to see that THERE SHOULD BE NO RF AT ALL.  Then check the very right
torroid for that band different from the RX band, 80m. THERE SHOULD BE NO
RF AT ALL there also.  Get out of TUNE mode.  Do these steps for every
relay in the LPF pertaining to a different band than 80m.  If you find
bad relays, replace them.  This should bring your power back up.   You
will have to redo the BPF alignment, to get full power out on all bands. 
Remember while waiting for the relay replacements not to use the bands
without relays.  You can use the other bands, but DON'T TX on bands
without a relay.

This information is an accumulation of thoughts from the Elecraft team,
et Gary Surrency.  If you are having anymore problems, or this
information did not help you contact Gary at: gary@elecraft.com

Also check everything in the LPF and the rest of the board for torroid
spacing adjustments, missed soldering a pad, cold grayish color soldering
points.  Check Q7 and Q8 with the K2 off, for high impedance on the B & C
leads, and a short to GND on the E lead, if so your PA transistors are
good.  Check T1-T4 transformers on the last sheet of schematics for the
RF board, for proper winding, tinning of leads, and placement of the
red/white/green leads.  Make sure these are wound according to the book.

Daniel
kg4dni


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