Power Output Drop and Calibration Issues on Flex 8400M

Rickyfly

I am opening a ticket to request technical assistance for my Flex 8400M but while I'm at it I'll also expose it to the community:

The radio is experiencing a significant and band-selective
drop in RF power output. Although 100W is selected in SmartSDR, the
actual power output varies drastically across bands:

• 20 meters: 95W (Near full power)
• 12 meters: 93W (Normal operation)
• 17 meters: 81W
• 15 meters: 75W
• 10 meters: 70W
• 6 meters & Low Bands (40m/80m): 50W (Strictly locked / Power Foldback)

The
fact that the radio can deliver over 90W on certain bands proves that
the LDMOS final transistors are physically intact. However, the severe
degradation on other frequencies suggests either a corrupted PA
Calibration Table in the firmware or an efficiency issue with the
internal Low Pass Filter (LPF) relay matrix.

Troubleshooting steps already performed:

1. Power Supply Check: Checked with a heavy-duty power supply. Voltage remains rock-solid at 14.2V under load, with no voltage sag.
2. Antenna & SWR Check: Antennas have been verified using a VNA. For instance, on 6m, the SWR
   is 1.38:1 with a purely resistive impedance, yet the radio still limits
   output to 50W.
3. Software Configuration: Checked
   TX Band Settings; all bands are set to 100% max power. DAX audio
   streaming from JTDX (FT8) is working properly and driving the TX stream.
4. Deep Factory Reset: Performed a full hardware factory reset (holding the power button until
   the LED turned solid White). The issue persists even on a clean,
   default profile database.
5. Diagnostic LED Flash: During one of the reboot cycles after the reset, the radio temporarily halted and threw a "1 Red Flash" error code (Fan/thermal controller alert) before booting up again.

Given
these symptoms, it seems the radio needs a forced PA Gain and Power
Calibration Routine via a remote session, or a physical inspection of
the LPF board.

On 17 meters, the SWR is a perfect 1.1 with 0.0W reflected and a
rock-solid 14.6V on the PA. However, the output is limited to 81.0W.
This is the definitive mathematical proof that the issue is strictly a
corrupted internal software calibration (PA Gain Table) and has nothing
to do with external antenna factors or foldback protection."

Best regards,

Riccardo