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Author Topic: Yaesu FT 950 - No RF output.  (Read 5524 times)
VK6NDT
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Posts: 38




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« on: September 04, 2010, 07:09:01 PM »

Hi folks, so the story goes, my son got into the radio room and found the variable voltage knob on the power supply. 16+volts while the FT950 was turned on. Now there is no RF output.

I have gone through and checked the menu to make sure its still set at 100% power and i have also performed the full reset on the radio hoping, just hoping it went into some silly state because it noticed the voltage increase but no luck.

from 160 - 30m there is less then 5w output and from 20m - 6m it goes as high as 8w.
My thoughts are that the PA transistors have not liked the extra couple of volts one bit and have packed it in.

Your thoughts? Cheers Jono VK6NDT
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KE3WD
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Posts: 5694




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« Reply #1 on: September 05, 2010, 08:37:43 AM »

Your thoughts may be correct.  Typically the finals get power directly from the supply with no intervening regulation circuitry inside the radio.  16V is typically the upper limit (standard is "11 to 16VDC). 

However, you should look inside the rig and see if there may be some sort of fusing arrangement between that power line and the PA amplifier stage.  Sometimes it is in the form of fusible resistors of low resistance and if you are lucky, they have popped and thus protected the much more expensive finals.  I don't have time to download and peruse the schematic of the 950 right now, good idea for you to do that, tracing that 13.8V from power input to the finals, looking for some component in between that could serve as a sacrificial fuse. 

If you are lucky. 

If not, well, you know where that is going...

New finals.

That 5W output is a ray of hope, though. 

Good luck, OM

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VK6NDT
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Posts: 38




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« Reply #2 on: September 10, 2010, 05:57:08 PM »

Just a little more info.

3.5Mhz - 0.09W @3.7A
5Mhz - 0.07W @3.8A
10Mhz - 1.8W @5.4A
14Mhz - 10.2W @8.4A
21Mhz - 15.7W @8.76A
28.4Mhz - 35.3W @9.6A
50Mhz - 47W @10.7A
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KE3WD
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Posts: 5694




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« Reply #3 on: September 11, 2010, 07:24:48 PM »

Sounds like it may be in the Low Pass Filter switching. 

Look for a stuck relay, or bad relay driver, something like that could be keeping one of the filters always on. 

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VK6NDT
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Posts: 38




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« Reply #4 on: June 15, 2011, 08:01:39 PM »

Just thought id post an update.. turned out that it was the Final PA. After speaking to Yaesu i found out that they would look at it for me, repaired and returned under warranty and the turn around time was fantastic.

Hasnt skipped a beat since Smiley
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N4NYY
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« Reply #5 on: June 16, 2011, 02:24:56 PM »

That is fantastic!
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KA5N
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Posts: 4380




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« Reply #6 on: June 17, 2011, 06:05:42 PM »

First thing I would do is to get a power supply that doesn't have a voltage setting
knob on the front panel.

Allen
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VK6NDT
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Posts: 38




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« Reply #7 on: June 19, 2011, 06:54:46 AM »

Power supply has been "upgraded" to a fixed voltage now, although makes it a little bot of a pain when it comes to project work.

I am how ever a little shocked i guess that there wasn't some protection in the radio but a simple fix and its all good now Smiley
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AD6KA
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Posts: 2232




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« Reply #8 on: July 04, 2011, 06:14:03 PM »

Sounds like you dodged a bullet, mate!
Kids & pets! Dontcha love 'em?

I was noodling about on 20m CW one afternoon when the
tree trimmer guy came to the door with a question. I went out
to talk to him for maybe 10-15 minutes. As I walked back toward the shack
I heard an uninterrupted string of Morse dashes. One of my Abyssinian cats had
fallen asleep on the shack desk with her head against that side of the paddles!
(Ham sounds: bleeps, beeps, sqwuaks, digimodes, all the cats are used to them) :>
Thank God it was one of the few times I've used the rig's speaker in QSO.
%99 of the time I use headphones! If THAT had been the case and I
had been even more distracted, who knows how long my cat would have been
on the air? I was sure I was going to be DF'd and get a letter from the FCC.

Ken,  AD6KA
« Last Edit: July 04, 2011, 06:16:27 PM by AD6KA » Logged
VK6NDT
Member

Posts: 38




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« Reply #9 on: July 19, 2011, 06:38:58 AM »

I hope your cat was correctly identifying ha-ha yes kids and animals can be great when it comes to ham gear.
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K2CMH
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Posts: 275




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« Reply #10 on: July 21, 2011, 10:22:23 AM »

So I guess when you got the cat off of the key, he became an SK (Silent Kitty)?   Grin
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AD6KA
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Posts: 2232




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« Reply #11 on: July 22, 2011, 12:40:37 AM »

So I guess when you got the cat off of the key, he became an SK (Silent Kitty)?   Grin
Heh. Good one, but nahh, she's too much fun.

Another one of them has the nickname "RTTY Kitty" because he camps out
on the back of my operating chair during contests. For hours! He's absolutely fearless.
I have an AL80A with no "Voltage Inrush" circuitry. Consequently
sometimes if I turn it on and the AC voltage cycle happens to be at the exact
spot in it's sine wave, the transformer becomes an electromagnet for
120th of a second before the PS caps load. The AL80A's case is steel,
so there's a loud BANG!
Even if the cat is near the amp, or sometimes even ON TOP of it,
he is so used to that sound it doesn't even faze him! The cat does nothing. It's amazing!


Does anybody else have the problem of cats liking to scratch/rub up
their chin on the nice hard rubber "big knob" on their rigs?
I am forever having to push "lock" to prevent that!
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K2CMH
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Posts: 275




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« Reply #12 on: July 28, 2011, 12:36:16 PM »

>So I guess when you got the cat off of the key, he became an SK >(Silent Kitty)?   Grin
>Heh. Good one, but nahh, she's too much fun.

Oops...I think you took that the wrong way...I didn't mean it in the traditional meaning of SK, but rather that she was no longer keying the transmitter...lol

Cats are fascinating animals, I have one myself, and she is a lot of fun as well.
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