[Elecraft] KAT1 Problem

[Niel Wiegand]

I'm having trouble getting my new KAT1 through initial test.

My K1 (s/n 750) MCU is marked "109E" and returns 109 for the version
level and my KAT1 has firmware version 1.2. I'm testing into a dummy
load. My problem shows up with either of two filter boards installed and
I confirmed normal operation without the KAT1 installed.

I can step through the ATU menu just fine and all of the relays work but
I do not get r8.5 when tuning in the Fx.x mode. Instead I see
continuously/randomly varying Px.x from 0.1 to about 5.0. In normal
operation now when keying my K1 the display shows 6 bars no matter what
power level setting but it has no measureable power output. I do hear
the signal, though, on another radio. If I put the ATU into tune mode
and then tune I do have measurable output and the relays clatter
searching for a good match. Keying the rig after this results in a
second or two of output before the K1 shuts down output power.

I used a scope to look at the SWR data signal from pin 3 of U2 on my
KAT1 to pin 2 of U1/MCU on the K1 front panel board as the "r8.5" test
is running. Pin 3 of U2 shows a clean digital signal running between 0
and about +5VDC. Pins 1/2 of U2 show the same sort of signal but with a
lot of RC time constant round off. Enough, in fact, that many
transistions towards 0 volts only go down to about 3 volts. This same
poor quality digital signal shows up on pin 2 of U1/MCU.

It appears that the MCU is not recognizing the output from KAT1/U2 as
digital SWR data. It is interpreting the signal as analog data and
displaying the changing analog value during the "r8.5" test.  

I've checked for problems/shorts around U2, D3 and associated parts. I
also pulled T1 and checked that transformer. I've also looked at the RF
Output detector area on the RF board. R36 is lifted and C43 appears to
be the correct value (.01mfd). D3 on the KAT1 board is also oriented
correctly and checks good with an ohm meter.

When running the KAT1 r8.5 test, does a clean digital signal normally
show up on pin 2 of U1/MCU?

This sounds to me like a bad U2 on my KAT1. Any other ideas?

Thanks es 73,
Niel - W0VLZ