Agilent power supply; output NOT zero! (+Video)  [Solved] - Page 1
Forum section: electronics / repair

author: The E Engineer
author_rank: Newbie
timestamp: October 13, 2018, 09:00:10 pm
content: Dear all,This is my first post but i have been here as a guest for many years. Today I need your help.I got an Agilent E3648A, used from ebay. The first channel does not go all the way to 0.00V. The minimum I can set is 0.3x volt and this voltage remains even when the output if OFF!When I set the voltage to 8V for example, and disable the output, the power goes down to 0.3V not as instantly as the 2nd channel goes.Any idea what the problem is?Thank you in advance-Update1: The behavior is like the output capacitor remains charged even when the power supply is disconnected from the mains. So the 0.3v stays and gradually goes down.-Update2:See it in action:-Update3: its solved, please see my reply to this post

author: Magiciaen
author_rank: Contributor
timestamp: October 14, 2018, 11:05:23 am
content: I know that on the E3631A, there was a firmware update to fix this very problem.https://www.keysight.com/main/editorial.jspx?cc=GB&lc=eng&ckey=1000004506:epsg:faq&nid=-34466.963148&id=1000004506:epsg:faqhttp://literature.cdn.keysight.com/litweb/pdf/E3631A-04C.pdfI wouldn't be surprised if it's the same issue on your E3648A.

author: The E Engineer
author_rank: Newbie
timestamp: October 14, 2018, 12:04:09 pm
content: Quote from: Magiciaen on October 14, 2018, 11:05:23 amThank you for the reply,That may be true, but the second channel is exactly 0.00v when the output is off or set to zero!I've checked my firmware, its 1.7-5.0-1.0. But I could not find any info regarding the latest available firmware and whether or not these units are up-gradable.Do you think this behavior is normal?Any other thoughts?

author: HighVoltage
author_rank: Super Contributor
timestamp: October 14, 2018, 02:18:36 pm
content: I have a 3649A and it goes to zero right away on both channels.Something is for sure wrong with your PSU

author: The E Engineer
author_rank: Newbie
timestamp: October 14, 2018, 02:29:54 pm
content: Guys, I'm glad to say that i found the problem and its fixed nowI found a broken track on the PCB which disconnected the output GND of the defective channel from MCR264-4 thyristor (pin #1).Here is the schematic if anyone is interested.http://ridl.cfd.rit.edu/products/manuals/Agilent/power%20supplies/E3646AE2.pdfThanks everyone!

author: HighVoltage
author_rank: Super Contributor
timestamp: October 14, 2018, 03:15:24 pm
content: Good that you fixed it.Sometimes these power supplies can be a challenge to fix.Why was the track broken?

author: Magiciaen
author_rank: Contributor
timestamp: October 14, 2018, 03:50:01 pm
content: Good job!!

author: The E Engineer
author_rank: Newbie
timestamp: October 14, 2018, 04:02:32 pm
content: Quote from: HighVoltage on October 14, 2018, 03:15:24 pmYes I'm lucky I didnt need to replace any of those obsolete parts.Not sure really how this happened, but it appears to be the art of high current. I wish I took a photo of the track to ask your opinion.I only do low voltage/current electronics so it may not be a problem for me ever, but if I had a 5A load I would do a stress test to make sure things wont go south if I ever happen to draw more amps than I usually do.So far everything seems to be alright.Quote from: Magiciaen on October 14, 2018, 03:50:01 pmThanks

author: HighVoltage
author_rank: Super Contributor
timestamp: October 14, 2018, 04:24:52 pm
content: These Agilent PSUs have a "crowbar" installed.So, be careful, to never turn it off, when you have a battery or a good charge capacitor hooked up.You will see magic smoke and it will burn away traces.May be that is what happened to yours.

author: The E Engineer
author_rank: Newbie
timestamp: October 14, 2018, 04:29:13 pm
content: Thanks for the tip. I will keep that in mind

author: coromonadalix
author_rank: Super Contributor
timestamp: October 14, 2018, 08:02:47 pm
content: Strange there is no revese biaised power diode on the Q503 and Q109 irf540 mosfetsStill strange the output protection diodes cr126 and cr127 in parallel ?Glad you repaired it