Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 22nd 16, 09:31 PM posted to sci.electronics.repair
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Default Troubleshooting RFI from switch-mode PS

On Monday, November 21, 2016 at 3:12:13 PM UTC-5, Dave Platt wrote:
In article ,
Jeff Liebermann wrote:

Having a component last longer than the warranty period is considered
wasteful by many manufacturers. Therefore, they select the cheapest
possible part that will work up to when the warranty expires but no
longer. The result is a product where every component blows up at the
same time, just after the warranty expires. The 10 flat screens in
your example will not show one bad component. Instead, there will be
dozens, all different brands and values. This is not due to crappy
manufacturing, but rather due to careful selection for the MINIMUM
lifetime of the component.


That's an "honorable" American tradition that dates back at least a
century. The story goes that Henry Ford has his engineers buy and
disassemble scrapped Ford cars, to see which parts had failed and
which ones were still in good shape. He pointed out that the company
could often save money by redesigning (more cheaply) parts which
rarely failed... so the new versions would wear out and fail at about
the same time as everything else.


Much further back than that:

by Oliver Wendell Holmes (1809-1894)
Have you heard of the wonderful one-hoss shay,
That was built in such a logical way
It ran a hundred years to a day,
And then, of a sudden, it — ah, but stay,
I’ll tell you what happened without delay,
Scaring the parson into fits,
Frightening people out of their wits, —
Have you ever heard of that, I say?

Seventeen hundred and fifty-five.
Georgius Secundus was then alive, —
Snuffy old drone from the German hive.
That was the year when Lisbon-town
Saw the earth open and gulp her down,
And Braddock’s army was done so brown,
Left without a scalp to its crown.
It was on the terrible Earthquake-day
That the Deacon finished the one-hoss shay.

Now in building of chaises, I tell you what,
There is always somewhere a weakest spot, —
In hub, tire, felloe, in spring or thill,
In panel, or crossbar, or floor, or sill,
In screw, bolt, thoroughbrace, — lurking still,
Find it somewhere you must and will, —
Above or below, or within or without, —
And that’s the reason, beyond a doubt,
A chaise breaks down, but doesn’t wear out.

But the Deacon swore (as Deacons do,
With an “I dew vum,” or an “I tell yeou”)
He would build one shay to beat the taown
’N’ the keounty ’n’ all the kentry raoun’;
It should be so built that it couldn’ break daown:
“Fur,” said the Deacon, “’tis mighty plain
Thut the weakes’ place mus’ stan’ the strain;
’N’ the way t’ fix it, uz I maintain,
Is only jest
T’ make that place uz strong uz the rest.”

So the Deacon inquired of the village folk
Where he could find the strongest oak,
That couldn’t be split nor bent nor broke, —
That was for spokes and floor and sills;
He sent for lancewood to make the thills;
The crossbars were ash, from the straightest trees,
The panels of white-wood, that cuts like cheese,
But lasts like iron for things like these;
The hubs of logs from the “Settler’s ellum,” —
Last of its timber, — they couldn’t sell ’em,
Never an axe had seen their chips,
And the wedges flew from between their lips,
Their blunt ends frizzled like celery-tips;
Step and prop-iron, bolt and screw,
Spring, tire, axle, and linchpin too,
Steel of the finest, bright and blue;
Thoroughbrace bison-skin, thick and wide;
Boot, top, dasher, from tough old hide
Found in the pit when the tanner died.
That was the way he “put her through.”
“There!” said the Deacon, “naow she’ll dew!”

Do! I tell you, I rather guess
She was a wonder, and nothing less!
Colts grew horses, beards turned gray,
Deacon and deaconess dropped away,
Children and grandchildren — where were they?
But there stood the stout old one-hoss shay
As fresh as on Lisbon-earthquake-day!

EIGHTEEN HUNDRED; — it came and found
The Deacon’s masterpiece strong and sound.
Eighteen hundred increased by ten; —
“Hahnsum kerridge” they called it then.
Eighteen hundred and twenty came; —
Running as usual; much the same.
Thirty and forty at last arrive,
And then come fifty, and FIFTY-FIVE.

Little of all we value here
Wakes on the morn of its hundreth year
Without both feeling and looking queer.
In fact, there’s nothing that keeps its youth,
So far as I know, but a tree and truth.
(This is a moral that runs at large;
Take it. — You’re welcome. — No extra charge.)

FIRST OF NOVEMBER, — the Earthquake-day, —
There are traces of age in the one-hoss shay,
A general flavor of mild decay,
But nothing local, as one may say.
There couldn’t be, — for the Deacon’s art
Had made it so like in every part
That there wasn’t a chance for one to start.
For the wheels were just as strong as the thills,
And the floor was just as strong as the sills,
And the panels just as strong as the floor,
And the whipple-tree neither less nor more,
And the back crossbar as strong as the fore,
And spring and axle and hub encore.
And yet, as a whole, it is past a doubt
In another hour it will be worn out!

First of November, ’Fifty-five!
This morning the parson takes a drive.
Now, small boys, get out of the way!
Here comes the wonderful one-hoss shay,
Drawn by a rat-tailed, ewe-necked bay.
“Huddup!” said the parson. — Off went they.
The parson was working his Sunday’s text, —
Had got to fifthly, and stopped perplexed
At what the — Moses — was coming next.
All at once the horse stood still,
Close by the meet’n’-house on the hill.
First a shiver, and then a thrill,
Then something decidedly like a spill, —
And the parson was sitting upon a rock,
At half past nine by the meet’n-house clock, —
Just the hour of the Earthquake shock!
What do you think the parson found,
When he got up and stared around?
The poor old chaise in a heap or mound,
As if it had been to the mill and ground!
You see, of course, if you’re not a dunce,
How it went to pieces all at once, —
All at once, and nothing first, —
Just as bubbles do when they burst.

End of the wonderful one-hoss shay.
Logic is logic. That’s all I say.

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Old November 22nd 16, 10:59 PM posted to sci.electronics.repair
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Default Troubleshooting RFI from switch-mode PS

On Monday, November 21, 2016 at 7:20:48 PM UTC-8, wrote:

1) the PS is ...
3) nothing has changed for 7 years until recently so this is definitely recent noise coming from the PS as I can switch to a deep cycle battery instantly and the RX noise disappears.

I have ordered the two 1000uF, 200V input caps and should replace them in about 3 days and will let you all know the results.


The input filter capacitors serve no RF function, so won't solve anything related to RF noise.
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Old November 23rd 16, 01:41 AM posted to sci.electronics.repair
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Default Troubleshooting RFI from switch-mode PS

whit3rd wrote:


I have ordered the two 1000uF, 200V input caps and should replace them
in about 3 days and will let you all know the results.



The input filter capacitors serve no RF function, so won't solve anything
related to RF noise.



** The OP is clutching at straws, big fat & expensive ones at that.

He ought to very carefully check the AC supply connection from his PSU to ground - any resistance there due to tarnished pins would send EMI way up.

BTW:

a portable AM-SW radio can be used to "sniff" for the source of the EMI.


..... Phil
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Old November 24th 16, 01:12 AM posted to sci.electronics.repair
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Default Troubleshooting RFI from switch-mode PS

Phil: thanks for your comments. Yes, I am grasping at straws - I fully realize that, and as I somewhat expected, replacing the input caps did nothing to alleviate the noise.

I have checked the AC connection to ground and that is all OK.

And I have also attempted some time ago to use your trick of a small SW receiver to attempt to find the noise but cannot pin down any one component as the culprit as the noise seems to emanate from all over the output section.

I am loath to start replacing any more caps until I really determine where it is coming from...
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Old November 24th 16, 01:23 AM posted to sci.electronics.repair
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Default Troubleshooting RFI from switch-mode PS

wrote:

Phil: thanks for your comments. Yes, I am grasping at straws - I
fully realize that, and as I somewhat expected, replacing the input
caps did nothing to alleviate the noise.

I have checked the AC connection to ground and that is all OK.

And I have also attempted some time ago to use your trick of a small
SW receiver to attempt to find the noise but cannot pin down any
one component as the culprit as the noise seems to emanate from all over the output section.


** I did not intend that meaning - the small AM-SW radio should tell you if the EMI is being radiated by the AC lead entering the PSU plus cabling in the premises.

With the covers on, the PSU itself ought not to be radiating any distance at all - at least with low power drain during receive mode.

Does the PSU have an inlet filter ?

http://www.westek.com.au/wp-content/...et-Filter.jpeg

This would be the first suspect.


..... Phil


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Old November 25th 16, 05:31 PM posted to sci.electronics.repair
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Default Troubleshooting RFI from switch-mode PS

On Mon, 21 Nov 2016 19:20:43 -0800 (PST), wrote:

I will respond to some of the posts above, without discussing the side topic of poorly manufactured capacitors etc.

1) the PS is rated at 35A, but I rarely draw more than 18A - and that is not a continuous draw.
2) I run the PS in a cool room, and also as a result of point 1 above the cooling fan has never come one (but has been tested to work). In other words the PS runs very cool
3) nothing has changed for 7 years until recently so this is definitely recent noise coming from the PS as I can switch to a deep cycle battery instantly and the RX noise disappears.

I have ordered the two 1000uF, 200V input caps and should replace them in about 3 days and will let you all know the results.


If the output inductor of the filter fails, the unit may continue to
run with excessive ripple current in the output filter and excessive
switching noise, due to increased peak currents.

The filter caps will eventually fail too, bulging or otherwise, due to
increasing ESR.

You would see abnormal output ripple voltage, even with good caps, if
the output choke has failed.

I've seen this twice in KW rated single-output supplies, but below 12V
output in both cases. Due to age, it meant rewinding the choke, rather
than replacing it (and replacing previously overstressed caps...).

Output ripple was evident (10x normal) even though there was a two
stage filter.

RL


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