E4406A died PSU

[Nemo1956]

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? 

[strawberry]

Some pictures can help
What chips?

[_Wim_]

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.

[Bondguy]

@ _Wim_:If multimeter was not enough, what method did you use to find out that those switching diodes were faulty?

[_Wim_]

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...

[kxenos]

Here is the service manual:
http://www.keysight.com/upload/cmc_upload/All/E4406-90178.pdf?&cc=GR&lc=eng

Look at page 31. The manual has no schematic diagrams because "The instrument assemblies are not repairable to the component level" (p.14) 

[Nemo1956]

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?

[lasvegas]

SO, how far did you get?
I have the same issue.

[Tony_G]

Posted a follow up on the CLIPs here - https://www.eevblog.com/forum/repair/vsa-e4406a-need-schematics-its-dead/msg3189270/#msg3189270

TonyG

[WernerFalken]

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.

[ik8tng]

Can you send more info? Where are the cap?
Sergio