PA100D PTT Pblm

General discussion

PA100D PTT Pblm

Postby KC2EE » 30 Jun 2013 20:22

I have just reconfigured my station and placement of the PA100D & have the following problem:
When powering up the amp, the "Operate" mode is "Standby" . With the PTT left open. when I press "Operate" it goes into "TX" mode.
Thus I can only use the amp in this manor. "Stby" to receive & manually pres "Oper" to go into "TX". & the same to go back to "STBY" to rcv.

Thus, I am manually changing the PTT operation, as if the circuit when active is in "TX". I have to go into "STBY" to rcv.
Evidently the PTT circuit is not working properly. It is as if there was a physical external to the PTT, or something happened internally.

Thanks for your input

Sid KC2EE
KC2EE
 
Posts: 3
Joined: 03 Sep 2012 11:21
Location: USA

Re: PA100D PTT Pblm

Postby KH2BR » 01 Jul 2013 05:56

Disconnect all of the cables except for power. Try it again. Did the malfunction go away when you switch to operate?
KH2BR
 
Posts: 29
Joined: 13 Nov 2011 07:01
Location: USA

Re: PA100D PTT Pblm

Postby 5B4AIY » 01 Jul 2013 07:17

OK, let's see if we can explain what's going on here. It will be essential to download the schematic for the MAIN BOARD, T/R, ATTENUATOR, CURRENT SENSE. The logic associated with the transmit/receive switching is on the lft-hand side, and is the T/R socket with !KEY-OUT and !KEY-IN (NOT-KEY-OUT, NOT-KEY-IN - negative logic, active low.) TR1, TR2, and the TRX socket.

Since you have not said with what transceiver you are using the amplifier, there are two possibilities, JUMA TRX-2 or TRX-1 or a non-Juma transceiver. In any case, do the following, connect the linear amplifier to a 50 ohm dummy load. Remove all cables including the RF input, except for the power cable. Switch the amplifier on. If you are using my firmware, then the amplifier will power up in the STDBY mode, if you are using the original firmware, it will power up in the last selected mode, which may be OPER.

Select the OPER mode. Does the amplifier still go into transmit? If so, then the fault is with the internal logic, which I will describe later. If not, then the fault is in the external connections.

Internal Logic
If the fault is internal to the amplifier, then this is how the internal logic works. There are two ways for the amplifier to be placed in the TX state.

1. Via a keying voltage on the RF input connector (This is the standard Juma TRX-1/TRX-2 transceiver method.)

2. Via a ground applied to the tip of a 3.5mm plug inserted in the T/R socket, the !KEY-IN line.

Method 1 - RF I/P Connector
The Juma TRX-1 and TRX-2 transceivers apply a +12V keying voltage to their RF O/P sockets when they are in the TX mode. This voltage is current-limited to about 1mA by a resistor in the transceiver so that no damage occurs if this voltage is shorted to ground. The voltage is sensed by R1 at the TRX RF I/P socket of the amplifier, and this resistor is bypassed to RF via C2. This voltage, identified as JUMA KEY IN on the schematic, forces D1 into conduction and is applied to the gate of TR2, forcing it into conduction, which repeates the inverted keying voltage on the !KEY-OUT line. In addition, this voltage is passed via pin 10 of J5 to the DDS/Display board where it is connected to pin 17, the KEY input sense line of the microprocessor. When the microprocessor senses a logic high on this line, it activates the transmit circuitry.

Method 2 - External Keying
In this mode the transmit/receive state is governed by the logic input to the !KEY-IN line of the T/R socket. In the receive state, this line is high or open, and as a result the gate of TR1 is held high by R3, forcing TR1 to the OFF state. With a logic low or a ground applied to the !KEY-IN line, TR1 is forced into conduction, and the voltage at R4 is high, placing a high on the KEY line, which is sensed by the microprocessor as before, asserting the transmit state.

Diode D1 in the JUMA KEY IN line is reverse biased in this state, thus ensuring that no DC key voltage is reverse fed to the connected transceiver.

Fault Finding.
It is necessary to first determine whether the fault is with the RF I/P connector line or the T/R line. First, short the RF input socket centre pin to ground. Did this clear the fault? In other words, if the RF input has a DC short on it, does the transmit/receiver logic now work correctly?

It is unlikely that there is a DC voltage present at the RF input socket, but it is necessary to make sure.

Now, plug a 3.5mm stereo patch lead into the T/R socket, and with a multimeter measure the DC voltage on the tip - it should show a logic high - if the multimeter has a 10M-ohm input impedance, you will see +12V on this pin.

Now measure the DC voltage on the ring terminal, it should show zero. To further check, set your multimeter to the low ohms range and with the negative lead connected to ground, and the positive lead connected to the ring terminal, you should measure a very high resistance, essentially an open-circuit.

To prove that TR1 is working, when you ground the tip of the patch lead the resistance measured between the ring and ground should drop to a very low value, typically between about 2 ohms and 5 ohms.

In all probability there is a fault associated with TR1 which is causing it to conduct and place a logic high on the KEY line. If this is not the case, then you may have an open circuit connection between pin 10 of J5 and the DDS/Display board. If this connection is open, then the microprocessor will sense a logic high on pin 17 and that will be interpreted as a transmit command. In this case, carefully check the ribbon cables, as well as the continuity of the connections on the DDS/Display board. It is not unknown for a poor soldered joint to initially work, but to go open after being moved or otherwise disturbed.

If you need any more assistance, let me know, and I'll try to help.

73, Adrian, 5B4AIY
5B4AIY
 
Posts: 178
Joined: 13 Nov 2011 09:22
Location: Cyprus

Re: PA100D PTT Pblm

Postby KC2EE » 01 Jul 2013 14:17

Thank you Adrian & Robert for suggestions.
It's good to know that KH2BR is here in the states if I need help/repair...
First, my PA100D has version 1.04 software & was assembled in Finland for me. I am using non JUma radios with amp. KX3, SDR Cube (modified to use TRX2 12 keying option, and various Military Packsets at 4 watts output.

With regards to Adrian's Fault finding items. I removed input/output cables & still had the Stby/TX operation. THere was no DC voltage present on input or output Coax's.
-Shorting the RF input socket, this did not clear the problem
-Stereo patch cord plugged into T/R socket: Multimeter shows +12vdc whether in Stby or TX.
-Measuring DC voltage on ring terminal shows zero, whether in Stby or TX
-Measuring ohms on Ring terminal to ground shows 4 ohms in both Stby or TX. NOT high/open as would be normal!
-TR1 operation: Grounding tip to sleeve yields 4 ohms, never high!

Is this showing a faulty TR1 ??? Or something else ??

Thank you for your help..

Sid
KC2EE
 
Posts: 3
Joined: 03 Sep 2012 11:21
Location: USA

Re: PA100D PTT Pblm

Postby 5B4AIY » 02 Jul 2013 05:25

Hi, Sid,
Yes, you definitely have a fault with the Tx/Rx switching logic. The fact that you measure essentially zero ohms on the ring terminal at all times means that either TR2 is shorted, or, more likely, that it is permanently turned on. This in itself would not affect the Tx/Rx switching, TR2 is only used to repeat the incoming !KEY-IN line to the output pin of the T/R socket in order to control an external antenna switch or other even higher power linear.

To prove that this is so you will need to remove the top cover, and measure the DC voltage across Z1/R5/C4 on the main board. These components are clearly marked, but unfortunately are located beneath the Frequency Sense module. It is JUST possible with a fine probe to reach the R4/C4 junction. You can also measure this voltage on pin 6 of J3, the F-SENSE board.

Remove the bottom cover, and place the amplifier upside down on the table, with the rear panel facing away from you. J3 is the set of 8 pins immediately in front of and to the right of the RF input socket. Pin 8 is nearest the rear panel. Pin 1 is nearest the front panel, and is connected by a long trace to pin 2 of J5. Measure the voltage on pin 6.

With the amplifier switched on and in the OPER state with all cables disconnected except for the power lead (Obviously!), you should see 0V - if you measure a significant +ve voltage, then this indicates that TR1 has failed short-circuit. Z1 is there to limit the positive voltage to a maximum of +5V for the logic input to the _RB5, pin 17 input to the microprocessor, so if TR1 has failed s/c then you will in all probability see +5V there all the time, which is why the microprocessor is commanding the linear into the transmit state when you release the STDBY inhibit by selecting OPER.

If this is the case, then by shorting pin 6 of J3 to ground you would remove the transmit command, and the amplifier should then return to the receive state. Shorting pin 6 of J3 to ground is safe, the current through TR1 is limited by R4, the 10k resistor, to about 1mA to 1.5mA. Just be certain that it is pin 6 of J3 you are shorting!

If this is so, then time for some Tender Loving Care!

73, Adrian, 5B4AIY
5B4AIY
 
Posts: 178
Joined: 13 Nov 2011 09:22
Location: Cyprus

Re: PA100D PTT Pblm

Postby KC2EE » 02 Jul 2013 15:27

Adrian,
I can't thank you enough for your assistance. Yes, your diagnosis is correct! I read 5 vdc at R4/C4 junction, in STBY or TX.
I then shorted J3-6 to ground, amp changed state from "TX" to "Operate". TR1 will have to be replaced.
I am not sure what caused this but I do have some PTT questions:
1. I am using a Mono, not Stereo plug in the PTT socket. I short sleeve to pin, to switch to "OPERATE". Shall I use a stereo plug with the ring floating ??
2. I am using a few different radios with the PA100D. I am using an external Mono lead with a switch to short the PTT socket when I want to TX.
I take care to short the PTT input, prior to introducing RF into the amp.
I am keeping the input RF wattage to 5 watts or less to operate. I introduced 15 watts once in error, but amp worked!

I do have a KX3 as well as a K3, but only use the KX3 at QRP levels, as I can use the K3 for QRO. I am a CW op, but I like to use my Military Back Pack sets in SSB for Nets associated with Mil Radios. That is when I am using the PA100D These Mil radios have NO external PTT circuitry available, so I manual execute the PTT short just prior to transmitting.. I almost forgot, I do use the Cube SDR which Juha told me how to modify the RF line as in the TRX2 radios.
Would I see any benefit in upgrading from version 1.04 to your current software ?
Again, thank you for your most valued input.
Sid KC2EE
KC2EE
 
Posts: 3
Joined: 03 Sep 2012 11:21
Location: USA

Re: PA100D PTT Pblm

Postby 5B4AIY » 03 Jul 2013 06:06

Good morning, Sid,
Glad to be of assistance. Pity about TR1, but it is an easy fix, there is plenty of room around it on the board, and it is easy to remove without damaging the printed circuit board. I generally use two soldering irons, one touching the two leads on one side of the device, the other touching the single lead, and the transistor then almost immediately pops off and sticks to one of the soldering irons. Clean up the board with a little flux and some solderwick, and solder the replacement device in, and you're done.

1. It is always a good idea to use the correct plug, but in this case since TR2 is open drain, and there is no voltage there, using a mono plug will not hurt it in any way.

2. It is fairly easy to make an automatic RF switch for the PA-100D so that when using it with a military backpack that does not have a keying output it automatically switches into transmit. Send me an email and I'll give you some details on how to do this with a simple circuit that should do the trick.

3. Using my firmware! Well, I would be delighted if you did, quite a lot of people do use my firmware and seem to be happy with it. You could download it from this website, or, again, if you send me an email I'll let you have both the latest Pa-100D firmware as well as the loader package and instructions on how to perform this little operation. My firmware modifications incorporate the necessary changes to get the PA-100D to operate with the KX-3 and automatically change bands as well as switch between Tx and Rx, so, yes you would see a benefit. There are also a lot of other features that you might like as well.

I would certainly reccommend making the RF switch for your PA-100D, you will find it so much easier than manually having to key the amplifier.

Send me an email to: adrian04@cytanet.com.cy

and I'll let you have the whole package.

Once again, always happy to help.
73, Adrian, 5B4AIY
5B4AIY
 
Posts: 178
Joined: 13 Nov 2011 09:22
Location: Cyprus


Return to Juma Discussion

Who is online

Users browsing this forum: No registered users and 1 guest

cron