K3 Very Low TX Power below 14 MHz

[Andrew UK]

Hi Does anyone have any idea what has happened: Scenario: TX cal will not work as there is zero watts on 1.9 MHz K3 Died on TX while tuning up on 1942KHz on an AL-811H Ameritron Amplifier, which had word fine previously. The LPA transistors, bias was upset, and Q2 not getting as hot as the others, however, all 3 replaced and bias set: it made not difference: I get the following: I performed a factory reset and recalibrated from scratch and reloaded all the firmware Automatic Transmitter gain will not run as there is zero watts on 1.9 MHz Symptom: 1. 160 M TX power 0 Watts 1.85 Amps SWR no reading 2. 80M TX Power 0 Watts 1.85 Amps SWR no rea 3. 60M TX Power 1 Watt 2.03 Amps SWR no rea 4. 40M TX Power 1.5 Watts 2.2 Amps SWR 1.1-1 5. 30M TX Power 4.5 Watts 2.8 Amps SWR 1.0-1 Fault code err TxG Filter problem? 6. 20M TX power 10 Watts Max 4.7 Amps SWR 1.0-1 7. 17M TX power 10 Watts max 4.7 Amps SWR 1.0-1 8. 15M TX power 8 Watts 4.6 Amps SWR 1.0-1 9. 12M TX Power 8 Watts 3.9A Amps SWR 1.0-1 10. 10M TX Power 9 Watts 4.18 Amps SWR 1.0-1 11. 6M TX Power 8 Watts 2.7 Amps SWR 1.0-1 My original MAX RF power was around 16 Watts on all bands except 6M What could be effecting the drive on low bands to fall to zero? and attenuating the RF power on the high bands power? If the AL 811H (which is not the best engineered amp in the world) provided a strange match or sent power from self-oscillation back to the K3, what else could it affect in the K3? RX seems affected to 20M, 17M, 12M, 10M and 6M all give S9 for 50µV Low Bands below at 50µV 160M S5 80M S8 40M S6 30M S8 These all gave S9 before the fault, so a big clue to the fault Any suggestions where I should start looking, as the RX path is down as well? Is this the biggest clue (Fault code err TxG) on the 30M band? I have made some measurements over the weekend and found the following Using a scope probe in to and R & S FSU spectrum analyser I have been tracing signals on 14 MHz which can give up to 10 Watts, and 1.9 MHz which give zero watts. 1. I have Checked D26,D31 and D27 they seem to check out and switch. 2. D25 seems to have a large DC volt drop on RX and TX 0.9 of a volt! Large for a schottky diode, with 20mA going through, calculated by the volt drop across R48 (should be 0.3V according to the spec sheet) 3. The TX signal is good at W21 on 1.9 and 14 MHz roughly the same. (D1 checks out on a meter) 4. Both signals are amplified through the LPA to the same level on the drains of Q5 and Q4 FETS, but still no RF power on 1.9 Mhz I know A scope probe is not the best way to measure; what does D1 S1M do on the LPA? Controlled by 12T, presume a RF O/P switch? 6dB attenuator is in all the time. What would stop LF (1.9 to 10MHz) being amplified? C23 on the LPA board 100PF is missing I presume this is correct? any suggestion welcome 73's Andrew