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Author Topic: Audio/Video Receiver Failure during amp tuning  (Read 2986 times)
N4CR
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Posts: 1650




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« Reply #15 on: April 02, 2013, 05:47:39 AM »

Another point of clarification, the A/V receiver shut it self down twice during tuning into the dummy before it shut down for the third and final time and did not come back on (according to the XYL).

You were tuning into a dummy load when it died?

This seems strange, but it means RF is leaking somewhere. With a dummy load, the near field RF should be minimal. Certainly less than 100 watts into an antenna.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
N1FAM
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Posts: 13




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« Reply #16 on: April 02, 2013, 10:19:09 AM »

The tuner is a Vectronics HTP-1500.  The G5RV is an off the shelf Radiowavz 102' G5RV.  From the center insulator to the so-239 connector is a 29' length of 300 ohm twin lead instead of ladder line.  I put the coil of coax at that point based on Radiowavz instructions, some discussions with their tech, and after reading a little on RF.  My understanding being that the purpose of the coil is to eliminate any RF coming back into the shack.  I thought I was OK on grounds but I do plan on cleaning joints, checking wire runs and seeing if I can shorten anything and/or beef up any of the wire.  Most is now braided or solid gauge 10 or better (meaning heavier).  Was thinking of trying to go to flat braided ground strips.  At least from each individual piece of gear to the aluminum bus that they all terminate in before leaving the building on their way to the ground rod buried in the soil.
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N1FAM
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« Reply #17 on: April 02, 2013, 11:49:09 AM »

Just read Phil's (NC4R) comment.  The dummy load is an old military ME-165G dummy load.  My understanding is that even when you are going into the dummy a small amount of RF is going into the antenna so you can tune it as well as it is a low output test that all is well in the antenna.
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KE3WD
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Posts: 5694




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« Reply #18 on: April 02, 2013, 12:12:07 PM »

Look. 

A Chinese made component in the A/V receiver's power supply crapped out. 

This happens quite a lot, actually, and most of the people who lug the things into our shopo for repair have nothing that generates transmitting RF like we do. 

The chinese 7805, 7812, 7815, 7912 and 7915 three-terminal regulators die in these things all the time. 

If a switching supply, the chinese electrolytics often go south. 

And, yes, one of the symptoms may just be that the unit goes off a few times before never coming on again.  No RF of any worthy amount anywhere near the greater majority of 'em. 


73
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KC4MOP
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Posts: 729




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« Reply #19 on: April 02, 2013, 04:26:26 PM »

Look. 

A Chinese made component in the A/V receiver's power supply crapped out. 

This happens quite a lot, actually, and most of the people who lug the things into our shopo for repair have nothing that generates transmitting RF like we do. 

The chinese 7805, 7812, 7815, 7912 and 7915 three-terminal regulators die in these things all the time. 

If a switching supply, the chinese electrolytics often go south. 

And, yes, one of the symptoms may just be that the unit goes off a few times before never coming on again.  No RF of any worthy amount anywhere near the greater majority of 'em. 


73
This could also be the problem too. Just upped and died. The radio tuning was a freak accident.
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N4CR
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« Reply #20 on: April 02, 2013, 09:57:48 PM »

Just read Phil's (NC4R) comment.  The dummy load is an old military ME-165G dummy load.  My understanding is that even when you are going into the dummy a small amount of RF is going into the antenna so you can tune it as well as it is a low output test that all is well in the antenna.

Well, of course some RF leaks out. But it's not even a smidgen close enough to burn out components 50 feet away. It's like saying the butterfly that flew across the ditch next to the road caused your vehicle to flip and roll.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
N1FAM
Member

Posts: 13




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« Reply #21 on: April 03, 2013, 11:28:20 AM »

I probably should not have carried the term "RF Leak" forward in responding to your post.  What I was trying to convey is the ME-165G circuitry is such that when you are tuning the exciter into the dummy, by design, an amount of RF is put into the antenna so that you can likewise tune the antenna before going on line at the exciter power setting and without causing interference with anyone else or any spurious transmissions.  Off the top of my head I do not remember the amount but it is something like 10W or less.  Unlike most dummies that are independent of the antenna the ME-165G is, by design, not.  After you are all tuned up you put the ME-165G selector switch in "operate" which bypasses the dummy and puts your tuned amp and exciter into the matched/tuned antenna.  I always thought this was a neat feature of this particular dummy.  The purpose of this set up was to insure all was well in the field, with both the exciter and the antenna, before the operator went on line.  Sorry for any confusion.
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