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Old 28th Apr 2018, 6:54 pm   #1
Simon_V
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Join Date: Feb 2014
Location: Pembrokeshire, UK.
Posts: 51
Default Trio TS711 low or no RF power output

I am NOT going to call this definitive as I may want to add to it but it is a good starting point.

These radios are starting to show their age (aren't we all) but that said they are superb radios and more than capable of holding their own against some more recent radios. Audio quality on both RX and TX is excellent.

As long as you are sure you have not been transmitting into a bad SWR and that you have hopefully not destroyed the PA block because they are rarer than dentures for chickens then this is for you.

The first step is NOT to dive in there with a trimming tool, no amount of twiddling will correct the problem.

I purchased my TS711 knowing that it had an RF power problem. The seller was super honest with me and said he had changed the PA block which had made no difference. He also reported that the fan did not run.

The fan was the easy bit, it was hardly surprising that it did not run as the PA was outputting less than 1 watt so it never got hot enough to trigger it on.

Remove the bottom cover and then remove the RF unit (6 screws) 3 coax connectors plugged into this board, 2 Coax fly lead connectors that are plugged into the IF unit and a 5 pin multipole connector that supplies power and various control signals.

The coax plugs and sockets will probably benefit from a good clean, a cotton bud and a bit of contact cleaner should be good enough.

I have attached a couple of pictures that you can use as a guide.

Replace the following ceramic capacitors

C30 - 7 pF
C34 - 3 pF
C36 - 1 pF
C40 - 0.5 pF
C37 - 2 pF
C41 - 2 pF
C33 - 8 pF
C38 - 8 pF
C42 - 8 pF
C44 - 22 pF
C46 - 470 pF
C47 - 100 pF
C45 - 0.001 uF

At this stage on mine from cold I have a really nice 25 watts but this falls away as the radio warms up or I transmit and falls to around 10 watts. I have some more capacitors on order and I have a feeling I am going to end up changing quite a few 0.001 uf caps.

Something else I have noticed on mine is that the RF unit does some odd things if I cool the output transistor Q6 (2SC2538). I do have a new one of these and next time I have the cover off I think I shall change this component regardless as it is not exactly thermally stable which often happens with transistors.

Before I add any more to this a word of WARNING.

The PA output device Q1 (M57727) is capable of around 37watts according to the manufacturers specification sheet. Experience from other radio amateurs suggests that this is not a good idea as it shortens the life of the device. As I said in the beginning, as these devices are getting rare it's not worth over driving them so be careful not to push the PA beyond the rated 25 watts.
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Old 28th Apr 2018, 8:43 pm   #2
Simon_V
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Default Re: Trio TS711 low or no RF power output

Changing Q6 (2SC2538) which I was not happy with has resulted in a now pretty stable 15 watts.

It's not as much as I have seen the rig produce and changing a few more caps when they arrive I think will bring back my missing 10 watts.

Simon - GW6TKK
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Old 29th Apr 2018, 10:42 am   #3
Simon_V
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Join Date: Feb 2014
Location: Pembrokeshire, UK.
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Default Re: Trio TS711 low or no RF power output

Refering to my list in the first post.

On my radio working methodically and monitoring the power levels along the drive strip while also looking at the effect of heating or cooling.

The first 9 capactors C30 to C42 will give the biggest impovement to power output. It may not be anything like full power but should get things pretty stable and up to around 5 watts.

The drive from this stage to the PA to achieve the full 25 watts should be around 0.3 watts.

Nothing so far has come down to a single component, rather the effect has been cumulative and things have got better as I have gone along.

Simon - GW6TKK
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Old 2nd May 2018, 10:57 pm   #4
Simon_V
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Default Re: Trio TS711 low or no RF power output

Pretty much got it sorted out.

output is now a reasonably stable 25 watts.

I must say thank you to GW0PLP Don for letting me pester him to death giving me signal reports.

So here is what I replaced after I reached the 15 watts output. I could make it drop off to around 5 watts by warming the area around the input to the RF board.

C20 & C21 - 33pF
C23 & C24 - 10pF
C25 & C26 - 0.001uf
C27 & C28 - 12pF

Also

R18 & R19 - 10R One measured 11R and the other anything between 10.3R and 10.9R depending if it was warm or cold. Cooling these with freezer spray made the output swing wildly from anywhere from a few watts to nearly full power.

I also went along the entire driver strip peeking the coils L14,L15,L16 & L17 and trimmer capacitors TC1 & TC2. The 4 coils interact with each other so you may have to go through trimming them a few times.

Simon - GW6TKK
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Old 6th May 2018, 2:20 pm   #5
Simon_V
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Default Re: Trio TS711 low or no RF power output

It would seem I have not quite got to the bottom of this problem yet as my radio developed a mind of it's own the other day.

It had been a rock stable 25 watts but the weather has warmed up here and turned the radio on to be greeted with around 10 watts, the room was not very hot but warmer than it had been.

Your not going to like this and I would not mess with it if your not confident.

L10 which couples the T IF signal into the RF drive strip has a small tubular capacitor built into the coil base. I couldn't get my meter to give me any kind of sensible reading on the value of it and the coil was very sensitive to the slightest change in temperature.

After a lot of digging around I found the TR9130 uses almost exactly the same circuit and the value of the cap is 39 pF. I have changed it in mine but be warned it needs a lot of care! Also I had to completley re-align the entire strip

I am monitoring the results and will report back if I find more.

Simon - GW6TKK
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Old 16th May 2018, 11:04 pm   #6
Simon_V
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Join Date: Feb 2014
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Default Re: Trio TS711 low or no RF power output

Now this is significant so I thought I had better report it.

Something is still ultra temperature sensitive, not talking artificial warming or cooling just the ambient air temperature in the radio produced by being switched on.

I was monitoring the effects of this and writing down the results suspecting the varicap diode D7 which is connected to 9v on TX and CV which is a correction voltage from the PLL and still applies around 2v to this diode even in RX. The CV voltage is rock stable by the way.

While I had the board out I did a job I had been meaning to do which was change the 3 surface mount decoupling capacitors under L14 - L17 which are C29, C35 & C43 all 0.001uF.

The replacements are modern low ESR types and have made a huge difference. After some careful re-aligning I had 25 watts which I expected would reduce to about 10 watts if I left the radio on. Not so, some 7 hours later with all the covers on and I still have 20 watts.

Just need to find where the missing 5 watts are going now!


Regards


Simon GW6TKK
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Old 20th May 2018, 11:35 pm   #7
Simon_V
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Join Date: Feb 2014
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Posts: 51
Default Re: Trio TS711 low or no RF power output

I think I can finally call this fixed!

Feeling like a bit of a twonk because I lost sight of something really important.

If your power supply voltages are not right then pretty much nothing else will be either.

I did originally set all the voltages but as I have increased the power coming from the RF board I had not re-checked them and as the current being drawn has increased the closer the RF board came to giving the correct 0.3 W so the 9T (9 volts) rail was not able to maintain a steady regulated 9 volts on this rail. I did a few tests and its pretty easy to loose 10 watts in the blink of an eye if you reduce this rail to 8.5 volts.

If you have got up to where I was with 25 watts from cold that falls away without the radio in TX but just switched on then change C10 - 100uF 16v in the AVR unit. Something else I discovered that is important, if your messing around with the RF board (something I have done a lot of) each time you test make sure you have put the 6 screws back in this board and they are tight, the board does some strange things if it's not earthed.

This was not the root cause of the problems. As I said I bought this radio knowing it had an RF power issue and I started out with well under 1 watt. Changing all the ceramics I have listed (which potentially could be 30 years old) has given gradual increases in RF output.

So my final measurements tonight, with the radio far warmer than I would like any radio to be, full power 22.5 watts and stable. cooled down naturally and with a room temperature of 67 deg F 26 Watts and rock stable.

Onwards and upwards, I will start new topics for these. The previous owner complained that the radio was deaf and was using it with a pre-amp. I don't find that to be so, I can hear a Repeater that is some 60 miles away OK. It doesn't move the S meter but it does break the squelch. My friend Don GW0PLP who is some 30 miles away just about lifts the S meter to S2, on my Yaesu FT7900 on the same antenna he shows S7. We have an SSB net here on Thursday evenings and I know I am off frequency by about 4 or 5 KHz on SSB on RX & TX.

Regards

Simon - GW6TKK
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