by 5B4AIY » 19 Apr 2016 06:45
Good Morning, Paolo,
OK, let's see if we can determine what is wrong here. You have already demonstrated that the PA-100D has a fault, and therefore you can now disconnect your KX3. The following tests will serve to verify the TX/RX logic is working.
You will need to connect the amplifier to a dummy load, but do not connect a transceiver to the TRX I/P socket. You will need a standard 3.5mm stereo patch lead, with a 3.5mm stereo plug at each end. Plug this patch lead into the T/R socket on the rear panel. By grounding the tip of this patch lead, to a screw on the front panel, for example, you can manually switch the amplifier between RX and TX.
1. STDBY Logic
In the STDBY state the TX/RX logic is disabled. Ensure that the display shows 'STDBY' and ground the tip of the patch lead - there should be no response from the amplifier in this state.
2. OPER Logic
In the OPERATE state there are a number of checks that are made to ensure correct operation.
a. MANUAL Band Selection
Press the OPER button and place the amplifier in the OPER state, and verify that the display shows 'OPER'. Press the AUTO button and ensure the display shows 'M' for manual band selection. Using the BAND+ or BAND- buttons, select any band. Verify that the display still shows 'M OPER' and a band. Ground the tip of the patch lead. Verify that the display now shows 'M TX'.
Remove the ground and verify that the amplifier returns to the OPER state.
b. AUTO Band Selection
Since there is no transceiver connected, no matter what AUTO BAND mode is selected, there is no band indication, and thus the band display should show either '?' or '?!'. With the amplifier in the OPER state, ground the tip of the patch lead. Depending upon what firmware you have installed the display should show either 'NOP' (No Operation) or 'Err' Error.
These tests verify that the transmit/receive and OPER/STDBY and Manual/Auto band selection logic is working. If you do not get these results then there is a problem with the T/R logic hardware.
Now comes the fun part. Let me explain how the transmit/receive logic works so that you can do some fault finding. For this you will need to print the PA-100 Main Board Schematic - 1 T-R Attenuator & Current Sense. I am attaching this to this post to save you having to search for it. In the top left hand corner you will see TR1, TR2, TR3, and the T/R and TRX input sockets.
The amplifier can be switched into transmit in a number of ways. If you are using the Juma TRX-2/TRX-1 transceivers, then there is a +12V logic signal present at the TRX socket when the transmit state is required. This is coupled via R1 10k and decoupled to RF by C2, 1nF and then to D1 and pin 10 of J5 where it is recognised as the KEY logic signal. It is also sent to the gate of TR2. With +12V at this point TR2 conducts and repeats this logic signal to pin 3 of the T/R socket, which is the sleeve connection.
If you are using a KX3 or other transceiver with a PTT out signal, then this signal appears at the tip of the T/R socket. The logic signal is open circuit for receive, and ground or low for transmit. With a ground on the tip of the T/R socket this is conveyed via R2 1k to the gate of TR1, turning it on. This will cause it to conduct and there will then be +12V at R4, and the logic is then the same as with the TRX-2 +12V signal.
I suspect that in your case you will find that you always have a positive voltage at the junction of R4 and R5, and that this is providing a spurious KEY signal. You can check this with a digital multi-meter. In other words, you will probably find that TR1 has failed. The KEY signal is sensed via the I/O port of the microprocessor, and as a result of the OPER state plus the KEY state, then the +TX signal will be generated by the microprocessor, thus turning TR3 on and energising RL1, the transmit/receive relay.
You can prove this by disconnecting the patch lead, and temporarily shorting the junction of R4 and R5 to ground, in which case the display should immediately switch back to 'OPER', and RL1 should de-energise.
You can also check for a spurious KEY signal by checking the continuity between the ring connection and the sleeve of the patch lead plugged into the T/R socket. In the RX state, there should be an open circuit between the ring and sleeve, if there is a spurious KEY signal present, then TR2 will be forced into conduction, and you will find a short circuit between the ring and the sleeve.
Let me know what you find.
Adrian, 5B4AIY
- Attachments
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- PA100-Main-Board Schematic-1 T-R Attenuator & Current Sense.pdf
- Main Board T/R Logic
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