PA100-D OPER/STBY

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PA100-D OPER/STBY

Postby IZ2ZPH » 17 Apr 2016 14:33

Hello
my PA100-D has been worked as predicted for some time.
A few days ago, at power on, switching from stby to oper, causes my kx3 to becoming deaf, even without antenna connected. Much like a 60 db attenuator
No problem on tx side, power and swr are right. To restore rx signal, the unit must be set to stby
Any clue?
my setup
KX3 and dipoles or vertical, all within swr range
tnx
Paolo
IZ2ZPH
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Re: PA100-D OPER/STBY

Postby 5B4AIY » 18 Apr 2016 08:20

Hi, Paulo,

If the RF signals from the antenna are being severely attenuated, this can happen if RL1 is energised when it should not be. This will disconnect the transceiver from the antenna, and instead connect it to the amplifier's input attenuator. RL1 should only be energised in the OPERATE state when the transmit signal is present, it should be de-energised in the OPERATE state in the receive mode. When you switch to the OPERATE state, verify that the TX indication is not present, and in this state RL1 should be de-energised. Take a look at the PA-100D Main Board Schematic, T-R Attenuator & Current Sense.

In addition, since you are using a KX3, please make sure that your ACC2 I/O is set to OFF. (Press and hold the DISP button to enter the MENU mode. Select the ACC2 IO selection by rotating the OFS knob, and then rotate the VFO knob to select OFF.) You can also ensure that this is really off with a multi-meter. Press and hold the KEYER/MIC knob and set the RF O/P power to 0W. Connect your PTT cable to the ACC2 I/O socket, and then using your multi-meter on the OHMS range, measure the resistance between the tip and the sleeve connection. In the RX mode, it should show a very high resistance (In my case > 2M ohms), briefly press the XMIT button to put the KX3 into transmit, and now the resistance should show essentially zero, (again, in my case < 5 ohms.)

Let me know what you find.

Adrian 5B4AIY
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Re: PA100-D OPER/STBY

Postby IZ2ZPH » 18 Apr 2016 20:40

Hello Adrian
i've checked ...
Kx3 side all is ok
Pa100-d size not good... when switching to oper from stby the tx indication lights up.... even without ant and rtx
RL1 is energized!
another test
if the pa100 is in auto band mode switching to operate will not energize tr1 (NOP) on lcd and does not attenuate rf ....until tx is off
after activating ptt/rf tx stays on until switching twice on auto band button back to NOP
i hope to have clearly exposed the current status
tnx
Paolo
IZ2ZPH
 
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Re: PA100-D OPER/STBY

Postby 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
PA100-Main-Board Schematic-1 T-R Attenuator & Current Sense.pdf
Main Board T/R Logic
(56.22 KiB) Downloaded 260 times
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Re: PA100-D OPER/STBY

Postby IZ2ZPH » 19 Apr 2016 16:51

Adrian,
i've followed your path and .......
the last point is true.
grounding the joint between r4 and r5 the pa100d switch back to oper and returning to tx after removing the patch
so do you think i need to replace tr1? no problem for spourius key signal
tnx and cheers
Paolo
IZ2ZPH
 
Posts: 4
Joined: 17 Apr 2016 11:56
Location: Italy

Re: PA100-D OPER/STBY

Postby 5B4AIY » 20 Apr 2016 06:15

Hi, Paolo,

Yes, unfortunately if you have a +5V signal at the junction of R4/R5 when there are no leads connected to the T/R socket, then it means that TR1 has failed and must be replaced. It also shows that the I/O port sensing the KEY signal is working. If there had been no voltage at the junction of R4/R5 and you were still sensing a KEY signal, then this would have meant that the I/O port of the microprocessor had failed, and that would have been fatal.

In this case, replacing TR1 is fairly easy. You will need to remove the main board of course, and I have found that it is easier if you use two soldering irons with fairly wide chisel bits. If you apply both soldering irons to the board, one on the side where there are two leads, and the other on the single lead, then the transistor will usually simply pop up and stick to one of the irons. Then use some solder-wick to clean the pads, and finally solder in the replacement transistor. Take care not to overheat the board otherwise you risk lifting the pads!

Glad to have been of assistance.

73, Adrian, 5B4AIY
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Re: PA100-D OPER/STBY

Postby IZ2ZPH » 20 Apr 2016 07:28

Good morning Adrian
wow! what's amazing support!
Easy to read and easy to apply too.....with pinpoint precision
Not many brands have such approach with customers! :D :D
In a few days spares will be in my hands so the pa100 can perform as before.....
when a product is well designed even minor (or major) problems can be easily pointed and fixed.
thanks again and have a nice day
73 ciao
paolo iz2zph
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