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Author Topic: Kenwood TS-120S Output  (Read 416 times)
KD0AFQ
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Posts: 17




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« on: April 12, 2007, 08:31:10 PM »

Good evening,

I am a new ham and recently bought a Kenwood TS-120S for Phone and PSK31 use.  Obviously the radio is very old but cosmetically it is in very good condition and the power supply that it came with seems to work well.  

My question is this:  On 10 and 15 meters the radio has an output of about 100 watts.  The strange thing is that the radio keys without any audio modulation whatsoever, almost like it is in AM mode or something.  

On 20, 40, and 80 meters it only puts out about 10 watts but seems to at least "swing" properly in side band when I speak into the microphone.

My question is this....Do you think the radio just needs to be tuned?  Do I need new finals?  Do you have any recommendations on where i could have this done or do you think that I could accomplish this task?

I am moderately good with a soldering iron and could probably follow simple directions or schematics.  

Any help would be appreciated.

Thanks!
Steve
KD0AFQ
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N3OX
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« Reply #1 on: April 12, 2007, 08:45:49 PM »

"On 10 and 15 meters the radio has an output of about 100 watts. The strange thing is that the radio keys without any audio modulation whatsoever, almost like it is in AM mode or something."

What's your antenna?  This sounds like RF feedback to me.

I used to have this problem all the time when I was running an end fed wire with a tuner... RF would get into the microphone circuit and be rectified and that made an audio input that would keep the RF going.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KD0AFQ
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Posts: 17




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« Reply #2 on: April 12, 2007, 09:00:11 PM »

I am using a Inverted "V" slinky antenna that is inside my room.  I haven't been transmitting much because the SWR's are high and I don't yet have an antenna tuner.

Thanks
Steve
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N3OX
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« Reply #3 on: April 12, 2007, 09:07:58 PM »

"I haven't been transmitting much because the SWR's are high and I don't yet have an antenna tuner."

There's your problem... the antenna in your room will be very prone to feeding back RF into the radio and if the SWR is high, then the radio will reduce power to keep from damaging the finals... you must have an OK SWR on 10 and 15m but then the strong RF feeds back.  On the other bands, you only get 10 watts out because the radio is trying to protect itself from high SWR.

Work on getting the SWR down and when you do, try low power and see if you can succesfully transmit.

It's also worth figuring out how to get an outdoor antenna if possible, or at least putting some seperation between the radio and the antenna..

Radio's working fine...

73 and good luck,
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N6AJR
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Posts: 9890




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« Reply #4 on: April 12, 2007, 11:22:12 PM »

and remember. om ssb, there is no carrier, so no sound , no transmit power.  a long whistle or a Helloooooooooooooooooooooooooo ( into a dummy load of cours) will show pretty close to actual power.

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KA5IWO
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Posts: 131




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« Reply #5 on: April 13, 2007, 06:02:34 PM »

Get yourself a good tuner to lower the swr to acceptable levels. The TS-120s does have a high swr protection feature but do not rely on it 100%.
Also there are diodes on the RF board that are prone to fail and cause the power output showing even with no modulation. Any questions just ask, I have repaired a ton of the TS-120 and TS-130 rigs. They are still fine little workhorse hf rigs from the late 70's early 80's. If treated right and kept up they will still give you may years of service.
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K5EXE
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Posts: 54




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« Reply #6 on: April 13, 2007, 06:19:17 PM »

This is a common problem with these radios -- I got a TS-120 in a trade last year that had this problem.

To start, open up the radio (yes, open it up...you're a ham, aren't you?) and tighten ALL the screws on the printed circuit boards. Even better, loosen them and then tighten.

If this doesn't work, check out www.mods.dk for a more detailed -- and complicated -- fix.
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KA5IWO
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« Reply #7 on: April 13, 2007, 07:59:43 PM »

The actual fix for the 120/130 rigs is not too bad just a little tedious. It involves replacing a few diodes on the RF board that have become leaky.
Take your time and the outcome will be a fine little rig. All the info about this common problem/repair can be found in Kenwood service bulletins.
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VK2ACM
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« Reply #8 on: April 14, 2007, 05:06:45 AM »

Hi Steve,
Just a quick question, I have a question. What does the radio wattage produce on a good 50 ohm load such as a dummy load ? Just curious......73 Clint VK2ACM
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KD0AFQ
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Posts: 17




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« Reply #9 on: April 14, 2007, 07:33:28 AM »

Thank you for the response. I will give it a whirl!

Steve
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KD0AFQ
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« Reply #10 on: April 14, 2007, 07:34:27 AM »

I printed all the service bulletins last night, I will start looking at them today and see what I can find out.

Thanks for the help.

Steve
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N9FAA
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« Reply #11 on: May 21, 2007, 06:09:44 PM »

Hello:

I have taken over ownership of the TS-120S (the same unit mentioned in the blog here).

My initial check indicates a decent signal on 40m; but, very limited power output on 10-15-20.  I am wondering if there is a component in common with the final power amplifier on 10-15-20 and no 40.

Any ideas?

Thanks in advance.

Dave

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