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Author Topic: Yeasu 747 GX lossing power.  (Read 907 times)
WA9CFK
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Posts: 86




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« on: January 31, 2013, 08:40:15 AM »

Anyone seen this?

I have a Yeasu FT 747 GX that I bought new and have used for years.

Recently it is losing power. When I turn it on and transmit it runs about 90 to 100 watts. After a couple of minutes of CW it will gradually drop to 35 to 40 watts.

If I hook it up to a dummy load. I get 35 to 40 watts on 1.8 and 3.5 Mhz, a bit more on 7 and 10 Mhz; when I go to 24 and 28Mhz the unit keeps transmitting after key up until the delay kicks out. I have not tried it on SSB.

The unit is clean, that is no dust or dirt in the fan or on the circuit boards.

I just wondered if anyone has seen this before or more importantly where can I send it to get it fixed? 
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K5LXP
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Posts: 4448


WWW

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« Reply #1 on: January 31, 2013, 09:08:46 AM »

Check your DC supply right where it connects to the radio.   A bad fuseholder or a weak connector terminal can cause the symptoms you're experiencing.


Mark K5LXP
Albuquerque, NM
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KA4POL
Member

Posts: 1908




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« Reply #2 on: January 31, 2013, 10:33:24 AM »

This may be interesting: http://www.eham.net/ehamforum/smf/index.php?topic=42071.0
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KA5IWO
Member

Posts: 131




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« Reply #3 on: February 03, 2013, 09:14:24 PM »

You have a failing pre-driver or driver transistors or finals in the PA deck or it could be as simple as an electrolytic cap somewhere in the PA deck failing. Also check your voltage regulators in that radio mounted on the PA cabinet. Those rigs are prone also to bad solder joints when they get old.
I have repaired many of them.
Kevin
KA5IWO
ka5iwo@bellsouth.net
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W4HIJ
Member

Posts: 367




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« Reply #4 on: February 08, 2013, 10:00:28 AM »

Wondering whatever happened to  "freeze spray"?  Or whatever you want to call it. Back in my TV shop days when we were diagnosing problems like this we used it all the time. We'd wait for the TV to get good and warm and the problem to show itself and then we'd give the suspect component or area a little blast. If the problem went away, we were well on our way to finding the issue. Better than guessing. Since this problem has been seen before, there is a starting point but it might still take some detective work.
 Also, taking the handle end of a small screwdriver or an IF tool and lightly tapping around the suspect area doesn't hurt either. Found more problems that way that I can count.
73,
Michael, W4HIJ
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K7KBN
Member

Posts: 2762




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« Reply #5 on: February 08, 2013, 06:26:01 PM »

A lot of the "freeze spray" stuff was pure freon and one spray would cause the end of the world.
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73
Pat K7KBN
CWO4 USNR Ret.
KE3WD
Member

Posts: 5694




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« Reply #6 on: February 08, 2013, 08:24:56 PM »

Freeze Spray for electronics troubleshooting is still readily available from several different mfrs.  

http://electronics.mcmelectronics.com/search?cataf=&view=list&w=freeze+sprAY&x=0&y=0

Use it on pretty much a daily basis on the bench.  

There are plenty of chemicals other than freon that evaporate fast and thus will "freeze" the components.  

One time I realized too late that we'd forgotten to reorder the stuff.  Can was empty, went to the stocking locker and none left on the shelf.  So I went to the shop refrigerator, got a couple of ice cubes, crushed 'em, put them in a sandwich baggie with a little salt, tied it up tight with a couple of rubber bands and was able to use that to proof a leaky junction.  Improvise, adapt and overcome. 


73
« Last Edit: February 08, 2013, 08:27:13 PM by KE3WD » Logged
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