SOLVED : Help with troubleshooting a Hypex SMPS400A400  - Page 1
Forum section: electronics / repair

author: rfengg
author_rank: Regular Contributor
timestamp: April 16, 2024, 03:45:15 pm
content: Hi All,May I request anyone who has experience or has access to the schematics of the Hypex SMPS400A400 power supply module, some help and advice?I have a Rotel RKB-D8100 amp which has 2 of these Hypex SMPS400A400 modules......while one of them puts out the correct voltages, the other is dead.While I can start comparing the working vs the non working one, if anyone has access to the schematics or has experience on these, it would be most helpful.thanks

author: fzabkar
author_rank: Super Contributor
timestamp: April 16, 2024, 06:34:21 pm
content: Is this of any use?HYPEX SMPS400V11 PSU service manual:https://elektrotanya.com/hypex_smps400v11_psu_sch.rar/download.html

author: rfengg
author_rank: Regular Contributor
timestamp: April 16, 2024, 06:56:16 pm
content: Thanks fzabkar....already found this at the same url.

author: MathWizard
author_rank: Super Contributor
timestamp: April 17, 2024, 11:16:35 am
content: Other than how tight it's packed, it probably should be a pretty standard layout SMPS with a chip or two, having most of the circuitry, inside them.That little 8 pin chip on the top side, next to a small transformer, that should be the primary side controller, that gets some trickle of current from after the rectifier, as it's startup Vcc, then once it gets going, some winding on one of those transformers, will generate the working Vcc of the chip, and circuits around it.Does it have a Standby voltage on the secondary side ? That little transformer by the 8pin DIP could be for STBY, or it could be some gate drive transformer, but it looks big for that.That chip could just be for STBY 5V, and there's another chip doing the main switching of the big transformer.You don't have to plug it in, to check a bunch of stuff like for shorts or diode voltages, from the plug, inwards, to those big transformers. And same with the output side, starting from the transformers.Then if there's no apparent shorts,etc, I would solder on a few wires here and there, and power it up and check some voltages, like after the rectifier, and Vcc of any IC's.So does the other one do anything at all ? And noise, or does it try to make some voltages and then restart over and over ? If it's totally dead, something near the plug should be broken, like a fuse, or the rectifier.

author: rfengg
author_rank: Regular Contributor
timestamp: April 17, 2024, 02:01:02 pm
content: Thanks for your reply MathWizard.Quote from: MathWizard on April 17, 2024, 11:16:35 am

author: rfengg
author_rank: Regular Contributor
timestamp: April 18, 2024, 08:07:04 pm
content: After burning a couple of gallons of midnight oil, was finally able to get the Hypex SMPS400A400 up and runningFor the sake of others, have attached a pic of the offending part (circled in red) that caused the issues for me.As all semicons on the board tested alright, I moved to the electrolytics and to my dismay all 3 of the 220uF/35V caps (circled in red) were bad, with half the capacitance and ESR values in the 10's.Started with changing the two caps on the top of the pic, circled in red, which made no difference, but changing the lower one between the filter electrolytics, did the trick.....have all main and aux supplies working after this swap.Never have I seen ALL caps on a board of the same manufacturer in such a condition.....Hypex should STOP using these caps to save a few cents/pennies.The cap manufacturer is some entity called "RD" and whatever snakeoil they are filling these caps with , it aint working.The originals are all 220uF/35V/105C (yeah,sure) but since I had only 220uF/50V/105C, I went with those , though space is a bit tight, especially for the single one between the 2 huge electrolytic filters......the 35V part should be smaller in case you are able to get hold of them.

author: fzabkar
author_rank: Super Contributor
timestamp: April 18, 2024, 09:51:02 pm
content: It looks like a Samwha capacitor:https://www.google.com/search?q=capacitor+rd+samwhahttp://www.samwha.com/electric/http://www.samwha.com//electric/product/list_pdf2/RD.pdf

author: MathWizard
author_rank: Super Contributor
timestamp: April 19, 2024, 01:21:03 am
content: Ok glad you found the problem. I was looking at goolge images for the PSU name. Yeah that's not the same picture you posted, but that 8-pin DIP in that pic should also be a controller.The schematic fzabkar linked too looked pretty cool, with more to it than I expected (IDK the PSU tho). Some of the ways that one side of a circuit gets tied to another side, well IDK how to plan for that stuff. I'd like to see some block diagram model of what it's doing, or try and make some of it in LTS.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: April 19, 2024, 05:32:39 am
content: So its rotten capacitors again.I'm so fedup with this capacitor plague.

author: rfengg
author_rank: Regular Contributor
timestamp: April 19, 2024, 11:28:47 am
content: @fzabkar : Whoa....really surprised that the "RD" make is actually a Samwha.....being a S.Korean company didn't expect that they would be so pathetic, especially since Samsung uses a lot of these. No wonder that you cannot find Samwha at Mouser or Digikey.@MathWizard : Have attached the data sheet of the Hypex SMPS400A400......no schematics in them obviously, but there is a "block" diagram which is quite useless.....but in fairness, the data sheet helped me find out the ouput voltages at the various connnectors.BTW, the 8pin DIP is indeed a dual opto.SMPS400Axx0_15xx.pdf(976.81 kB - downloaded 171 times.)

author: beatman
author_rank: Regular Contributor
timestamp: April 20, 2024, 02:46:18 am
content: RD samwha 105c standart series.The worst thing for smps input or output and pwm amps.I use tons of these for recap cheap mixers and cheap crap amps that don't worth anything better.

author: Audio101
author_rank: Contributor
timestamp: July 24, 2025, 02:43:19 am
content: I just want to say THANK YOU!!!!! Thank you VERY much. I had the exact same problem and replacing those 3 caps got 2 of my power supplies up and running! MEGA Thank you!!!!Quote from: rfengg on April 18, 2024, 08:07:04 pm

author: rfengg
author_rank: Regular Contributor
timestamp: July 24, 2025, 01:43:22 pm
content: @Audio101 Glad you could get the problem sorted out....happy listening!!!The very essence of this forum and many other forums is that we each try to be there for one another....cheers