Hi,
Option 1:
Set the current limit real high and watch to see where the fire starts!
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl Van Wormer
Sent: Wednesday, January 13, 2016 12:43 PM
To: [log in to unmask]
Subject: Re: [TN] Post HiPot Testing, Power Supply leakage failure
Random thoughts:
Before going into the work required to find the fault location, test more
than one unit to see if the fault is in the design or just in one unit.
My HiPot testers raise the voltage (either manually (with a knob), or
automatically) until the desired voltage limit is reached, or the leakage
current is exceeded. Most units announce the excessive leakage with an
obnoxious buzzer that will make you pee your pants, since you are nervous
from being near a very high voltage. Before the limit is reached, there may
be visual (faint blue corona discharge) and/or audible (hissing or crackling
sound) clues.
Set up the test in a room that can get very dark, and then turn out the
lights and wait for your eyes to adjust. As you run the test, you may be
able to see the location of the corona discharge before the leakage current
limit is exceeded. Resist the temptation to use your finger, and use some
other insulated pointing device to mark the location before tuning on the
lights.
You can use a length (3 foot) of vinyl tubing (3/8 inch) with one end held
to your ear and the other end waved around the board to locate the area if
corona sounds are being generated.
If you cannot locate the fault area on external (visible) surfaces, the
breakdown is occurring inside of a component or inside the PC board. By
sequentially removing components that are across the voltage barrier (check
the schematic), and then re-testing, you can find which parts are the cause
of the problem. If all isolation components have been removed and the fault
still exists, it is in the PC board.
If the fault is in a custom component, like a transformer, you may want to
carefully disassemble the transformer to locate the defect area.
If these comments don't give you a good starting point, please ask a more
specific question. Everybody's entitled to my opinion . . .
Later,
Carl
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask]<mailto:[log in to unmask]>
http://cipherengineering.com<http://cipherengineering.com/>
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, January 13, 2016 8:12 AM
To: Carl Van Wormer <[log in to unmask]>
Cc: [log in to unmask]
Subject: RE: Post HiPot Testing, Power Supply leakage failure
Carl,
Thank you very much for sharing. This is the first time that I am
conducting Failure Analysis on a Post HiPot PS failure, nubby to the task.
I suppose that Thermal Imaging would be beneficial in isolation the
suspected failure, hot spot. I have no experience in
isolating/disconnecting various "HV barrier" components on the PS as you
stated. If you are willing to share some thoughts on this task I would
greatly appreciate the information.
Victor,
-----Original Message-----
From: Carl Van Wormer [mailto:[log in to unmask]]
Sent: Wednesday, January 13, 2016 9:14 AM
To: TechNet E-Mail Forum; Hernandez, Victor G
Subject: RE: Post HiPot Testing, Power Supply leakage failure
Perform the HiPot test in a dark room, slowly (and carefully) looking for
visible glow before onset of the leakage-limit event. This may help you to
visually locate the area of the breakdown. If it is not visible on any
exterior surfaces, you will have to disconnect various "HV barrier"
components to determine which one is breaking down internally.
Carl B. Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Engineering LLC
21195 NW Evergreen Pkwy Ste 209
Hillsboro, OR 97124-7167
503-617-7447x303
[log in to unmask] http://cipherengineering.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Wednesday, January 13, 2016 7:06 AM
To: [log in to unmask]
Subject: [TN] Post HiPot Testing, Power Supply leakage failure
Fellow TechNetters:
What type of failure mechanism is associated with a HiPot Test Failure on a
750W Switching Power supply? The visual did not turn up any damage to
components exterior structure. No damage to PWB laminate and solder mash
surface.
Victor,
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