TRX2 power out problem

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TRX2 power out problem

Postby F5UL » 22 Jun 2012 08:50

I'm working on a power problem on my TRX2!
You will find thereafter the power level and collector curent I found :

Band Power IC

1.8 2.8 3.06
3.5 1.6 3.05
7.0 2.5 3.04
10.1 3.8 2.81
14.1 4.0 2.80
18.1 12.0 2.06
21.1 11.0 1.98
24.9 13.0 2.22
28.5 12.1 2.09

What disturbed me was that, on the TR1 (BFG591) predriver on PA board the collector RF voltage was around 3.45 volts
on all bands, excluding the band pass filter part. The push-pull IRFR110 is balanced and on each collector I have around 6.0 volts.
The proble seems tied with the IRFI510, where I get a distinct variation depending on the band. I suspected the LowPass filter,
as the full output is obtained with the 30 Mhz filter. That would indicate that all lower frequencies lowpass filters are out of
use.
Does anybody have an idea about where to search for a reply?
Thank you in advance!
F5UL
F5UL
 
Posts: 3
Joined: 31 Dec 2011 09:29
Location: France

Re: TRX2 power out problem

Postby 5B4AIY » 24 Jun 2012 11:05

Hi,
Perhaps I can be of assistance.

You would do well to print out the three schematics that relate to this, the ALL BAND 10W POWER AMPLIFIER CIRCUIT DIAGRAM, the RF FILTER BOARD BPF SECTION, and the RF FILTER BOARD LPF SECTION.

How does all this work? In the receive mode RL1-A and RL1-B are de-energised, and the input antenna signal is routed from the antenna socket, J3 on the ALL-BAND PA board (top right-hand side) to pins 7 and 9 of J2. These pins connect to pins 7 and 9 of J3 on the RF FILTER BOARD LPF section (middle, top) to the right-hand side of the low-pass filters. Once through a filter's relays contacts, it appears on pins 2 and 4 of J3. This connects to pins 2 and 4 of J2 on the ALL-BAND PA, 9again, top right). It then goes via RL1-A, to RL1-B to pin 2 of J1 (bottom left-hand corner) where it is called RF. Pin 2 is connected to pin 2 of J1 of the RF FILTER BOARD (top left hand corner) where it is called RF2. RF2 is routed to C42 (right-hand side) and is fed through the FST3253 IC2 analog muliplexer chip to the band-pass filters. It then appears at the output of the filter on the left-hand side, routed through another FST3253 mux chip IC1, to C40, where it becomes signal RF1. This is connected to pin 2 of J2 (bottom left-hand corner) and is fed to the main board.

In the TX mode, the signal from the main board appears at pin 2 of J2 to become RF1, passes through the band pass filters and their multiplexers to become RF2. This then enters the power amplifier and now both RL1-B and RL1-A are energised, and so the drive signal passes through the attenuator whose attenuation is selected by another FST3253, IC1, and passes to TR1. The output from the PA appears at RL1-A where it is now routed to the RF filter board and through the low-pass filters to the antenna socket.

So, what can go wrong? Well, quite a lot. The first thing to check is to make sure that the filters are being selected. The selection is performed by IC4, 74HC595D on the RF FILTER BANDPASS board. It receives its SPI Latch, Clock, and Cascade signals, and the decoded outputs are the B0, B1, and B2 signals, as well as the !B2 (NOT-B2) signal generated by IC5. These are DC voltages, and you can check them with a multimeter. I suggest you make yourself a really thin probe! Set your transceiver to 200kHz, and check the voltages. B0, B1, and B2 should be zero volts, and !B2 should be +5V. Using the BAND SELECTION CODE shown in the table on the RF FILTER BOARD, tune the transceiver to each of the frequencies shown in the table, and verify that the B0/B1/B2 and !B2 signals are all there in the correct sequence.

This will show that the band-pass filter select logic is working.

The low-pass filter logic is derived from these signals by means of IC6, a 4028 decoder. As you check each of the signals from IC4, also check that one and only one decoded output is high on R13, R14, R15, R16, and R17 in turn. These signals energise the relays on the low-pass filter board via their respective transistors, in turn, TR1, TR2, TR3, TR4, and TR5.

Once you have verified that the filter select logic is working correctly, now turn your attention to the driver transistors. With zero volts on the gate of the transistor, it should be OFF, and there should be +14V (approximately - depends upon your primary power supply voltage) on the drain terminal. If the voltage is zero, then it could indicate a shorted transistor, or, more likely, an open circuit between the relay and the transistor. If the voltage at the drain remains at +14V even when there is +5V at the input gate drive resistor, then there may be an open circuit transistor connection, (Check thoroughly the soldered connections - as I have found, it is all too easy to miss one!) or a faulty transistor. These are FETs, and they are susceptible to static damage.

Verify that all the relays operate in this way, and especially that only the selected pair of relays operate, none of the others.

If the selection logic and the relay drivers and relays are OK, then it's time to investigate the filters themselves. However, before we go there, let me know how these checks work out. If these are all OK, then inspect the input band-pass filter connections very carefully, it is easy to miss solder joint and have only one side of a component soldered.

Adrian Ryan, 5B4AIY
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Location: Cyprus

Re: TRX2 power out problem

Postby F5UL » 25 Jun 2012 20:39

Hi, Adrian,
Thank you for your kind reply.
I will follow tomorow your indication and verify all circuits indicated.
I suspect the low pass filter, by instinct, as predriver and drivers look like they are doing there job.
But I will verify that
Good evening Adrian, c u tomorrow!
F5UL Bob
F5UL
 
Posts: 3
Joined: 31 Dec 2011 09:29
Location: France

Re: TRX2 power out problem

Postby F5UL » 26 Jun 2012 09:28

Hello Adrian,

You where right in the point!!!
The fault was RL-5, who was permanently exited. That was why the 18/28 Mhz was working OK (the relay already in place!)
and with the other low pass filters switched in, well the output was going down!!!
The culprit was TR5, (2N7002) shorted drain/ source!!!
Finaly we are most of the time, in need of somebody else indications!
Thank you for your help, Adrian, and who know, I may be of use to another Ham!
Now I can go finish the PA100D .
73 good day, Adran.
F5UL Bob
F5UL
 
Posts: 3
Joined: 31 Dec 2011 09:29
Location: France

Re: TRX2 power out problem

Postby 5B4AIY » 28 Jun 2012 15:52

OK, glad we managed to sort out the problem. Happy to be of service. Would you like to try my firmware modifications? If so I'd be happy to send you the latest build and the User Manual. Send me an email to: adrian04@cytanet.com.cy

There is also a new version for the PA-100D. If you have any questions on this, let me know, and I'll try to help.

73, Adrian, 5B4AIY
5B4AIY
 
Posts: 180
Joined: 13 Nov 2011 09:22
Location: Cyprus


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