wall wart: bad caps strikes again!

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  • eccerr0r
    Solder Sloth
    • Nov 2012
    • 8701
    • USA
    #1

    wall wart: bad caps strikes again!

    Well, shows to prove caps can be bad without looking it.

    I bought a 9V DC wall wart switching PSU from a thrift shop to power an 8 port 10/100 switch that was missing the power supply. However ... it was BAD! I got a few volts and then it goes to nothing under load. Can't light a light bulb with it at all.

    I used a vise to crack the case open and looked at its guts. No visible issues. Caps looked good - except when I stuck an ESR meter to them. They were off the chart (my homemade analog ESR meter doesn't deflect if it's more than 5 ohms.) I replaced those caps and the wall wart works once more - holding voltage constant under load.

    Alas re-sealing it would be an issue. Right now it's "sealed" by zip ties... Someday I'll go for the epoxy...that is if I really need this 8-port 10/100 switch again.
    Tags: None
    • ReeceyBurger123
      Never Give Up !
      • May 2014
      • 7325
      • Britain
      #2
      Re: wall wart: bad caps strikes again!

      Nice what brand of caps where they ?
      Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

      https://www.facebook.com/Telford-Tel...7894576335359/

        Comment

        • CapLeaker
          Leaking Member
          • Dec 2014
          • 8178
          • Canada
          #3
          Re: wall wart: bad caps strikes again!

          pictures... there has to be pictures...

            Comment

            • ChaosLegionnaire
              HC Overclocker
              • Jul 2012
              • 3264
              • Singapore
              #4
              Re: wall wart: bad caps strikes again!

              yea! this is a bad caps pr0n site! we demand pics! NPNT!

                Comment

                • eccerr0r
                  Solder Sloth
                  • Nov 2012
                  • 8701
                  • USA
                  #5
                  Re: wall wart: bad caps strikes again!

                  Not sure what brand the S is, but definitely not a good one...

                  There's the zip ties!



                  (bad caps are the 5mm and 3mm(?) units, 10uF/25V and 22uF/25V respectively; yes the small one has higher capacitance.)

                  I replaced them both with 5mm units.
                  Attached Files

                    Comment

                    • BleedCap
                      Member
                      • Aug 2015
                      • 30
                      • Malaysia
                      #6
                      Re: wall wart: bad caps strikes again!

                      http://capacitor.web.fc2.com/s_other.html#s2

                        Comment

                        • eccerr0r
                          Solder Sloth
                          • Nov 2012
                          • 8701
                          • USA
                          #7
                          Re: wall wart: bad caps strikes again!

                          Looks like that's it, more bad caps...

                          Not sure how they could use such small caps, that thing can't possibly be a low ESR unit...

                            Comment

                            • kc8adu
                              Super Moderator
                              • Nov 2003
                              • 8832
                              • U.S.A!
                              #8
                              Re: wall wart: bad caps strikes again!

                              those are not suitable for smps output filtering.
                              they lasted just long enough to get out the door and make whatever that unit shipped with run 31 days to get out of warranty.
                              i wonder how many more nasty surprises lurk in that thing?
                              things like no fuse,output lines too close to ac side,poor isolation in the transformer,ect.

                                Comment

                                • eccerr0r
                                  Solder Sloth
                                  • Nov 2012
                                  • 8701
                                  • USA
                                  #9
                                  Re: wall wart: bad caps strikes again!

                                  I didn't take photos of the internal guts but it actually didn't look too bad. It wasn't a cheap 2-transistor oscillator, it had an IC in it (that wasn't the optoisolator). It was able to detect out of spec situations and shut down. It probably still had a fuseable resistor for gross issues, but I don't remember (don't make me open this thing again! )

                                  But yes the manufacturer chose capacitors poorly.

                                    Comment

                                    • SteveNielsen
                                      Retired Tech
                                      • Jun 2012
                                      • 2327
                                      • USA
                                      #10
                                      Re: wall wart: bad caps strikes again!

                                      What's the brand of the PSU?

                                        Comment

                                        • eccerr0r
                                          Solder Sloth
                                          • Nov 2012
                                          • 8701
                                          • USA
                                          #11
                                          Re: wall wart: bad caps strikes again!

                                          Says "DENCA" on it, but no idea if this was an OEM or what...

                                            Comment

                                            • momaka
                                              master hoarder
                                              • May 2008
                                              • 12175
                                              • Bulgaria
                                              #12
                                              Re: wall wart: bad caps strikes again!

                                              Those can't be the output capacitors - no way! Maybe start-up caps, perhaps. Please tell me so!

                                              And "S" branded caps? Perhaps they didn't want to write the full name... i.e. "S***y"

                                              Also, epoxy may not work too well to glue the case - at least I had poor results with most epoxies. If the plastic is ABS, PVC cement will work great. Or if the joints are thin enough, super glue will work well too.
                                              Or as a last resort, hot melt glue. It's messy, but it actually works quite well. I just had to open the power adapter for my sister's laptop again (output power cord became shorted for the second time now). And let me tell you, that hot glue was holding the case shut tight. I had to use a sharp carpet knife to cut the glue at the seem on all sides to pry it open. The best part is that when I want to close it again, all I have to do is just re-melt the glue (either with the glue gun or hot air).
                                              Last edited by momaka; 10-07-2015, 07:37 PM.

                                                Comment

                                                • eccerr0r
                                                  Solder Sloth
                                                  • Nov 2012
                                                  • 8701
                                                  • USA
                                                  #13
                                                  Re: wall wart: bad caps strikes again!

                                                  Nope, those were output caps as far as I could tell, they were hooked up to the output! They were hooked up in parallel too I think. I believe the largest cap in it was the input filter cap and there's no startup cap... but now you guys really are making me want to open this thing up again and take photos of the guts to make sure I'm not seeing things...

                                                  Yeah I may have to look for a solvent type glue for sealing the case... I really don't like hot glue, at least I found it to be fairly flimsy. But you're right about the epoxy as there are plastics out there that it simply does not want to stick to (like the mixer/applicator that the epoxy came with )

                                                    Comment

                                                    • eccerr0r
                                                      Solder Sloth
                                                      • Nov 2012
                                                      • 8701
                                                      • USA
                                                      #14
                                                      Re: wall wart: bad caps strikes again!

                                                      Argh... Ok... yes you were right, momaka. Yes these were the startup capacitors. I didn't look deeper into the device, I thought that the output was right there, but nope, there were more capacitors deeper into the device. I had a gut feeling that these were indeed way too small for the current this device should provide. 1A with minuscule 22uF capacitors seems way too small. The output caps were actually two 1mF with a pi-like filter which is much more like what they should be.

                                                      Anyway this is a SM8002C switch mode IC. The separation between the primary and secondary is fairly large, looks like around 8mm or more on the foil side. Not sure how good the SM8002C ...

                                                        Comment

                                                        • goontron
                                                          5000!
                                                          • Dec 2011
                                                          • 4108
                                                          • US
                                                          #15
                                                          Re: wall wart: bad caps strikes again!

                                                          To reclose wall worts is get some scrap plastic of the same type and melt it along the seem with an old clapped out soldering iron.
                                                          Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....

                                                          "Dude, this is Wyoming, i hopped on and sent 'er. No fucking around." -- Me

                                                          Excuse me while i do something dangerous


                                                          You must have a sad, sad boring life if you hate on people harmlessly enjoying life with an animal costume.

                                                          Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore

                                                          Follow the white rabbit.

                                                            Comment

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