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Author Topic: Astron power supply hum  (Read 3821 times)
K6ELE
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Posts: 26




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« on: July 01, 2012, 06:00:04 PM »

My Astron 35A linear power supply has an intermittent hum (5-10 seconds, 1-3 times an hour) coming from the transformer.  I called Astron and they said tighten bolts on transformer to see if it would stop. Did that and still hummed.  Called again and they said transformer was failing and to send it back would replace transformer (was out of warranty), which they did.  Got it back and was DOA, so they sent me the PC board for it.  Installed the new PC board and started it up.

Still hums.  Opened it up and put rubber pads under transformer feet, still hums but less noticeable.

So I have been using it to run my Icom 7600 and letting it hum.

Question:  Is Astron correct that transformer is failing? And if so is it OK to run until it fails.  Or should I dump it and get different PS?

Thanks,
Ed
K6ELE
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WX7G
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« Reply #1 on: July 01, 2012, 06:03:31 PM »

I suspect the AC line voltage rises during the times you hear the humming. The transformer is beginning to saturate.

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AA4PB
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« Reply #2 on: July 01, 2012, 06:22:43 PM »

Does it hum when there is no load on it or with the receiver load or only when you are transmitting? I'm not sure how a transformer would start failing intermittently. Usually the windings either short or open and its done.

Do you see any change in DC output voltage when the hum starts? How about the AC voltage across the secondary of the transformer -or the primary line voltage?

Or, maybe its just humming because it doesn't know the words  Grin
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W6EM
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« Reply #3 on: July 01, 2012, 07:14:03 PM »

So, Astron replaced the transformer, and the circuit board and it still has the intermittent hum?  You might want to monitor the unregulated DC.  It could be a filter capacitor intermittent short that clears itself.  If they didn't replace the capacitor(s), that might be it.  It would show a dramatic drop in unregulated DC when the hum happens.

At any rate, the hum is likely from an intermittent heavy load causing enough external magnetic flux to vibrate the cabinet.  Especially since you're on your second transformer and they're both doing the same thing.

73,

Lee

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WX7G
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« Reply #4 on: July 02, 2012, 09:12:14 AM »

My Astron RS-20A hums when the line voltage rises to 125 VAC.
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KB1GTX
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« Reply #5 on: July 02, 2012, 11:58:32 AM »

Might want to check the grounding on your house?

Do your lights dim in the house when you turn on something like a toaster?
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KQ6Q
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Posts: 961




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« Reply #6 on: July 02, 2012, 12:53:57 PM »

I second the motion on checking the wiring. Some years back I would get a huge hum when I connected a modem to the phone lines. Solved the problem by getting an optically isolated modem. A while later, the electrical service to our mobilehome park required maintenance, and turned out there was a burned bus bar connection, resulting in a difference of several volts between AC ground and phone company ground -which caused the hum in my cheaper modem.
See what happens with a Ground Fault Interrupter, connected between your power supply and the wall...
Another solution - use a switching power supply - no transformer to hum!
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K8AC
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« Reply #7 on: July 02, 2012, 03:23:01 PM »

This has been covered so many times in so many forums.  I've owned 5 or 6 Astron supplies of all sizes.  They've all hummed.  In most of the cases, the hum is actually the paper thin steel cabinet, being excited by stray flux from the transformer.  Normally, one could tame this by using a sound deadening material on the inside of the steel enclosure.  But, because of the cabinet design, you can't do that.  Chances are that applying the adhesive-backed sound deadening material on the outside of the cabinet (primarily the top) would quiet things down.  The real answer is to stop buying high current power supplies with a non-toroidal transformer core housed in a thin steel cabinet. 

73, K8AC
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W6EM
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Posts: 692




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« Reply #8 on: July 02, 2012, 04:52:29 PM »

My Astron 35A linear power supply has an intermittent hum (5-10 seconds, 1-3 times an hour) coming from the transformer.  I called Astron and they said tighten bolts on transformer to see if it would stop. Did that and still hummed.  Called again and they said transformer was failing and to send it back would replace transformer (was out of warranty), which they did.  Got it back and was DOA, so they sent me the PC board for it.  Installed the new PC board and started it up.

Still hums.  Opened it up and put rubber pads under transformer feet, still hums but less noticeable.

So I have been using it to run my Icom 7600 and letting it hum.

Question:  Is Astron correct that transformer is failing? And if so is it OK to run until it fails.  Or should I dump it and get different PS?

Thanks,
Ed
K6ELE

After a while, sometimes threads go astray.  Ed has an intermittent problem, not a continuous one.  So, it isn't stray flux from continuous exitation.  And, not from over excitation, since it's intermittent.  Besides, let's give Ed the credit of monitoring his incoming AC line voltage to see if its dancing all around.  Besides, if that were the case, his lights would be doing the same thing.  Getting bright, then dim.  Loose neutrals on service drops can cause that to happen, but its very obvious.

There's something going on inside the Astron to cause it to intermittently hum and then go quiet.  Since the transformer was replaced by Astron as was the main PC board, about the only thing left would be the capacitors intermittently shorting.

Astron cabinet buzz is well known, as are other supplies like a Pyramid that I have with the cabinet close to the transformer core.  The buzz happens to mine on inrush when turned on, not continuously.

73.

Lee
W6EM

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WX7G
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« Reply #9 on: July 03, 2012, 11:22:39 AM »

Let's do an IBE or Inference to the Best Explanation. This is a problem solving tool that could lead us to the cause of the Astron power supply hum.

Evidence:

Unit hums intermittently
Transformer has been replaced
Regulator board has been replaced
Transformer has been tightened
Aluminum Electrolytic capacitors failing with increasing ESR and decreasing capacitance is by the far the most common failure mode (normal wearout mechanism)
Aluminum Electrolytic capacitors failing shorted is very rare and is due to a manufacturing defect (foil burrs)
Astron power transformers are known to hum at high AC line voltage


Explanation
(in the order of most likely to least likely):
AC line voltage is intermittently high
An Electrolytic capacitor is failing
Transformer is defective
Transformer is loose

« Last Edit: July 03, 2012, 12:08:38 PM by WX7G » Logged
K6ELE
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Posts: 26




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« Reply #10 on: July 03, 2012, 08:23:19 PM »

I appreciate all of the suggestions given regarding my problem. I still think its a PS problem because:
1. AC line has been checked and not high.
2. I ran an Aston 20 A at same location for 10 yrs until about 2 years ago when I upgraded equipment. No hum.
3. loaner Astron 20A was used for over a month here while Astron service had my A35. No hum with loaner.
4. A35 was OK for first 14 months, then started to hum.

I think at this point I am going to go back to a switcher, just did not want the fan noise.
Thanks again to all who replied.

Ed
K6ELE
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KA4POL
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« Reply #11 on: July 03, 2012, 10:11:18 PM »

Did you measure the input current? Does it change when the hum starts?
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WX7G
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« Reply #12 on: July 04, 2012, 09:27:20 AM »

Hypothesis and Experiment:

The AC line voltage needs to be continuously monitored and measured before, during, and after a hum event. If the line voltage rises during hum event the voltage hypothesis is proved.

The non-hum of the Astron 20 does not provide strong evidence for the line voltage hypothesis. It uses a different transformer than that used in the Astron 35 and might be designed to operate further from saturation.

The Astron 35 not humming for the first 14 months does not provide good evidence for or against the line voltage hypothesis. Line voltage can change over time as the power company changes things. The line voltage in the US has been rising for a number of years.

To test the failing capacitor hypothesis an experiment can be conducted. The Astron 35 can be loaded (a transceiver can be used) and checked for hum. If the hum does not appear the capacitor hypothesis is disproved.

To test the high line voltage hypothesis one of three experiments can be conducted:

1. One is to monitor the AC line current with an oscilloscope and a current transformer. The onset of transformer saturation is indicated by the current peaking sharply at the top of the AC waveform, especially during a hum event. This experiment provides data on how much margin the Astron transformer has.

2. Another experiment is to monitor the line voltage with a DMM or oscilloscope and wait for a hum event. If the line voltage rises during a hum event the line voltage hypothesis is proven.

3. And a third experiment is to apply a higher voltage using a boost transformer and a Variac. Raise the voltage and note at what point the hum, if any, occurs. If it does not hum at 130 VAC that is evidence against the line voltage hypothesis.





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AC5UP
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« Reply #13 on: July 04, 2012, 09:47:12 AM »

1. AC line has been checked and not high.
2. I ran an Aston 20 A at same location for 10 yrs until about 2 years ago when I upgraded equipment. No hum.
3. loaner Astron 20A was used for over a month here while Astron service had my A35. No hum with loaner.
4. A35 was OK for first 14 months, then started to hum.

Playing Devil's Advocate, I can see a few issues here:
1) The AC line voltage was not high during the test period. That's all you know for sure. Before or after the test could be otherwise, and was the supply humming when you were testing...? If not, you checked it at a time when everything was working properly.

2), 3), 4)  There is a graveyard a mile and a half north of me and it's my understanding that almost everyone in that graveyard was at some time in the past vibrant and healthy... Some for 70 years or longer. How does that relate to their present state of health?

 Wink

 
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K8AXW
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« Reply #14 on: July 04, 2012, 10:42:13 AM »

Since this and that has been replaced the other things have been tightened and what is left over has been checked and eliminated.

Why not grasp at a straw and replace the rectifier(s)??  'bout all that's left and they do cause hum on occasion.... like 60Hz hum and not 120Hz hum.  (I'm speaking of cabinet hum, not output hum)

Al - K8AXW
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