[Elecraft] [P3] P3 woes - repaired but now claims my K3s puts out 873W!

[Dave New, N8SBE]

Alan,

I tried changing the SensorCal entry, but you are correct there isn't 
enough range.  It only cut the reading by less than half.

When I change the MtrScale entry, it changes the meter scale, but it 
still shows over 800W (and runs over the smaller scales) in text on the 
screen.

I did a visual inspection of the sensor board, but without a schematic I 
couldn't check the resistor and capacitor values.  I couldn't find a 
schematic for the P3 TX Mon sensor board.  Do you have one handy?  I did 
find schematics for the sensors themselves in the W2 documentation.

And yes, the SWR is way low, about 1.5, compared to what my KAT500 shows 
for the antenna side of the tuner (I have one of those display boxes on 
the KAT500, so I can see all the tuner values).  I have the P3 sensor 
between my KAT500 and the antenna feedline using a short coax jumper 
between the KAT500 and the sensor, which is currently going to a 75 ft 
coax run to a ZS6BKW window-line fed dipole in an inverted vee 
configuration.  In the past, I've seen 'raw' SWR of 2.5 to 4:1 or so on 
80m in particular.  On 40m right now, I have 2.93 antenna SWR shown on 
the KAT500, which is corrected to 1.18 SWR reflected back to the KPA500 
or the K3s if the KPA500 is in bypass mode.  Given my setup, the P3 SWR 
should agree closely with the KAT500 antenna-side SWR, but it is about 
half.

73,
-- Dave, N8SBE

On 2023-04-07 17:15, Alan Bloom wrote:
> Hi Dave,
> 
> There is a "SensorCal" entry in the Transmit Monitor Menu, but I don't
> think it has enough range to correct such a large error.
> 
> There is also a "MtrScale" entry to set the full-scale power on the
> meter display.  Does the reading change when you change the scale?
> 
> In addition to the I/O board, the problem could also be on the Sensor
> board (the small board that connects the sensor RJ45 connector to the
> I/O board).  If one of the resistors on this board went open or
> shorted it could cause a power error.  Is the reverse power reading
> way off as well?  (i.e. does the SWR read wrong for SWR not close to
> 1:1?)  If so, that could be due to a resistor problem on the Sensor
> board.
> 
>> I'm wondering if the new revision I/O board is somehow incompatible 
>> with the older TX Monitor board,
> 
> No I don't think so.  There was a minor change in the sensor design at
> one point but it was just a capacitor change to improve the detected
> bandwidth so the envelope would display correctly.  (The same sensors
> are used for the W2 wattmeter.)
> 
> 73,
> 
> Alan N1AL
> 
> 
> 
> On 4/7/23 12:12, Dave New, N8SBE wrote:
>> So, I was the guy that had a P3 display/boot problem recently.
>> 
>> I sent it to the mother ship for repair, and they found that (get 
>> this) the 12V supply was shorted to the 3.3V supply (eep!).
>> So, a new(er) I/O board (which contains the supplies) and a 
>> replacement blown 3.3V LCD controller later, I have an (almost) fully 
>> functional P3 again.
>> 
>> EXCEPT, the TX Monitor function is now funky.  It claims that my K3s 
>> is putting out 873 (or so) watts!  I've tried both sensors (I had a 
>> 200W HF sensor on the shelf since I added a KPA500 and changed to a 
>> 2KW HF sensor), and although the scale max changes on the P3 display 
>> when I change sensors, it still way overstates my output power.  The 
>> KPA500 is showing 1360 watts on the P3!
>> 
>> I unplugged/re-plugged everything, did a visual inspection of the TX 
>> Monitor adapter board under a lighted magnifying glass, looking for 
>> missing/broken SMD resistors or caps, but so far no soap.
>> 
>> I'm wondering if the new revision I/O board is somehow incompatible 
>> with the older TX Monitor board, or maybe there is a missing 1M-ohm 
>> resistor to ground on the I/O board at the sensor connector, or an 
>> incorrect series resistor value there.
>> 
>> And yes, I sent a note to support, but I haven't heard back, yet. 
>> Wondering if anyone (Alan?) has any ideas where this behavior is 
>> coming from.  The wattmeter in both my K3s and KPA500 are working 
>> normally.  It's just the P3 wattmeter that's gone off the deep end, 
>> now.
>> 
>> Thanks, and 73,
>> -- Dave, N8SBE
>> ______________________________________________________________
> 
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