Author Topic: HP 3457A short circuit and smoke  (Read 2078 times)

maru

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HP 3457A short circuit and smoke
« on: August 22, 2017, 05:08:14 PM »
Hi,

Today I tested two  HP 3457A multimeters, I saved them from their journey to the garbage dump. I studied the two excelent youtube video's from this device.
We've got +220V  so I started with the first on 220v as we do with al our devices. First I did a successful the internal test. Then I checked the numbers of calbration (35).
So, I was very happy with my new device ..until I pushed some buttons OHM, DCI ACI and suddenly a sissy sound, a lot of smoke , terrible smell and a little panic! :o
I dissabled the power, and checked the fuse at the rear, but that is still intact! I can see a burning spot at the rear just above the power inlet. I didn't  power it up again cause I first want to check without the cover what's dammaged inside.

Now let's check if the other 3457A is working. Internal test OK, calibrationumbers: 54 Do the buttons
work???.....OMG :-[ same thing happens smoke and terrible smell ...but no damaged fuse?? I don't know it's important to tell but I don't have main earth in this room
Can someone please explain what I'm doing wrong?

Kind regards,



SeanB

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Re: HP 3457A short circuit and smoke
« Reply #1 on: August 23, 2017, 12:36:56 AM »
Very simple, the input mains filters or the class X and Y supression capacitors there have failed. Easy to replace, and a very well known failure on all HP/Agilent/Keysight equipment that uses those clear RIFA or Schaeffner made capacitors and filters in the mains inlet. They are well known to have the clear plastic craze, letting in moisture which then blows up the capacitors when mains is applied after being unpowered for a while.

maru

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Re: HP 3457A short circuit and smoke
« Reply #2 on: August 24, 2017, 03:12:02 PM »
Hi Sean,

Thanks for the help. That is indeed what has happened. On the inside, I saw no burned parts, only a trace of brown sticky mess. After drilling the pop rivets I could better investigate the power inlet. At the bottom are the data; brand and type. 

Now look for a replacement.
Are the values listed on the power inlet filter critical? Could I use these?
http://eu.mouser.com/ProductDetail/Schaffner/FN9222R-3-06/?qs=Eu63EZxBwKJlsItmQ9%252bOfg==





 


SeanB

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Re: HP 3457A short circuit and smoke
« Reply #3 on: August 25, 2017, 03:07:19 PM »
Yes, your one is made in 1988, so right when this was a future time bomb. New one will fit, and has an upgraded capacitor that is a lot less likely to do this again, and so long as it fits will work.

maru

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Re: HP 3457A short circuit and smoke
« Reply #4 on: August 26, 2017, 11:21:48 AM »
Great, last day's I found a spare part. It looks to me that this one has some kind of overpresure valve at one edge.
Today I took the part in place and extensively tested the multimeter without the cover (outside ;-). After an hour I thought it was time to put everything together and cleaned the frontpanel and enclosure. Now I've got a nice HP 3457A on my bench! Time to dive into the manual :)



Ronasaki

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Re: HP 3457A short circuit and smoke
« Reply #5 on: September 13, 2017, 05:40:34 AM »
Your information is very good.