E4406A died PSU - Page 1
Forum section: electronics / repair

author: Nemo1956
author_rank: Contributor
timestamp: November 11, 2016, 01:57:29 am
content: Hi all. Can anyone help me. I have a HP4406A with a died power supply. I have looked at this for some time but I can get the dam thing working. It seem the stand by +15 volts is missing so it wont do anything.I need to find a schematic for this power supply but I can find anything on the inter web.Has anyone had or seen this fault before?

author: strawberry
author_rank: Super Contributor
timestamp: November 11, 2016, 06:00:48 pm
content: Some pictures can helpWhat chips?

author: _Wim_
author_rank: Super Contributor
timestamp: November 12, 2016, 08:51:45 am
content: Check the switching diodes. I had 2 SMPSes were these had broke down. Warning: they measured ok with a multimeter, but there reserve breakdownvoltage was severly lower which caused the malfunction in the SMPS.

author: Bondguy
author_rank: Contributor
timestamp: November 12, 2016, 08:55:45 pm
content: @ _Wim_:If multimeter was not enough, what method did you use to find out that those switching diodes were faulty?

author: _Wim_
author_rank: Super Contributor
timestamp: November 12, 2016, 08:58:46 pm
content: I desoldered them and replaced by I know good one (after I saw with the scope something was not correct).But you could also desolder them and put for example 50V reverse voltage on them and check if they conduct any current... This is the problem with the multimeter, the testvoltage is to low...

author: kxenos
author_rank: Frequent Contributor
timestamp: November 12, 2016, 10:34:40 pm
content: Here is the service manual:http://www.keysight.com/upload/cmc_upload/All/E4406-90178.pdf?&cc=GR&lc=engLook at page 31. The manual has no schematic diagrams because "The instrument assemblies are not repairable to the component level" (p.14)

author: Nemo1956
author_rank: Contributor
timestamp: November 21, 2016, 03:07:55 am
content: Hi all. That's very interesting about the diodes. I have replaced so leaky caps but still not working.I will have a look at these diodes. but all I have is a digital meter to test them with. Is there a better way of doing this?

author: lasvegas
author_rank: Newbie
timestamp: August 13, 2020, 04:42:25 am
content: SO, how far did you get?I have the same issue.

author: Tony_G
author_rank: Super Contributor
timestamp: August 15, 2020, 02:20:54 am
content: Posted a follow up on the CLIPs here -https://www.eevblog.com/forum/repair/vsa-e4406a-need-schematics-its-dead/msg3189270/#msg3189270TonyG

author: WernerFalken
author_rank: Contributor
timestamp: April 15, 2023, 12:11:32 am
content: I had a PS from an E4406A that had the same issue (dead standby power). I traced it down to the little PWM board just before the transformer by removing the transformer and injecting 15VDC into that side at an appropriate spot. Used it that way for a little while, then acquired another E4406A in better shape. Used that one for years and finally circled back to this.Two caps: 47uf and 33uf. Both came in at 22uf, and ESR of around 20ohms @ 120Hz. I had an exact match for the 47uf, but had to use 22uf+10uf in parallel on the backside of the board to get it going (frontside has interference with the main caps).Works great now....Edit: Now that I think about it, though, that circuit is probably pushing far beyond 120Hz.... I haven't really looked at the datasheet for the SG3843D.

author: ik8tng
author_rank: Newbie
timestamp: October 02, 2023, 05:12:00 pm
content: Can you send more info? Where are the cap?Sergio

author: KE5FX
author_rank: Super Contributor
timestamp: October 24, 2024, 02:45:56 am
content: Quote from: ik8tng on October 02, 2023, 05:12:00 pmFor posterity, he was referring to these:My E4406A would generally boot up about 5-10 minutes after turning on the power, but lately it was taking more like 30 minutes to 1 hour so it was time to deal with it.The 47 uF cap showed higher-than-normal ESR when cold, but was close to normal when warm. The 33 uF cap was almost completely open. As Werner noted, these caps were originally mounted on the other side of the board, but this side is easier to access without desoldering the whole PCB.