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Testing Methodology Discussion Questions and comments regarding the testing methodologies used on jonnyguru.com

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  #21  
Old 03-06-2018
ashiekh's Avatar
ashiekh ashiekh is offline
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Quote:
Originally Posted by Stefan Payne View Post
No, you need 20MHz.
The plots above seem to show variations at the scale of just a few kHz (Time 10.0ms), and that circuit is from 1973 so I imagine components are better these days (45 years on)

Last edited by ashiekh; 03-07-2018 at 08:57 PM.
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  #22  
Old 03-10-2018
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Quote:
Originally Posted by Per Hansson View Post
Holy thread batman revival time!
Just a small question on this theme: what sort of setup for the capacitors do you folks use?
I have always neglected to do it: but when testing to rebuild this Seasonic PSU discussed here I found out the hard way that it really matters!
Not satisfied with the result after recapping it with LOW esr caps (actually motherboard grade) I bought some general purpose caps like the originals seems to be.
But the result was worse, but then I put on a 10F electrolytic cap and a 100nF film cap and most of the ripple I thought was there was gone, meaning it was mostly HF noise...
But holding those caps + probes and cables in close proximity made me feel there might be a prettier solution to this
I think that most testers (Sunmoon) used by the big sites contain the bypass caps inside the testing equipment right behind the BNC output jacks.
Anyway the Intel design guidelines are a bit wierd, the text reads:
Quote:
Ripple and noise are defined as periodic or random signals over a frequency band of 10 Hz
to 20 MHz. Measurements shall be made with an oscilloscope with 20 MHz bandwidth.
Outputs should be bypassed at the connector with a 0.1 F ceramic disk capacitor and a
10 F electrolytic capacitor to simulate system loading. See Figure 5.
Yet they then suggest these as candidates:
Filter Note:
0.1uf - Kemet, C1206C104K5RAC or equivalent
10uf - Vishay 293D106X0025D2T or equivalent

The latter of course being a Tantalum capacitor and not an electrolytic!
I think I'm just going to make a small board with alligator clips with these caps on it, and then put some shrink wrap over it all.
That will do fine for my uses
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  #23  
Old 03-10-2018
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Quote:
Originally Posted by Per Hansson View Post
I think that most testers (Sunmoon) used by the big sites contain the bypass caps inside the testing equipment right behind the BNC output jacks.
Not from factory, they don't. I had to install them on both SM-268s and the FastAuto. IIRC Tazz had to do the same thing on the SM-5500.

It does make a difference on some but not all units tested with them.
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