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Videoton VT-110, XT clone PSU repair

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    Videoton VT-110, XT clone PSU repair

    I was having trouble repairing this unit and while searching for info I came across another Videoton design. It came with the pc case and it was a cheap local sale so I picked it up, out of curiosity.




    This one is a full AT size unit that is functional but gave a strange whine/buzzing right from startup. After some poking around it was determined that the noise came from the main transformer. There was also a rattling sound when the unit is rotated or shaked. It turned out that on of the main trafos half core has been cracked and broken. There was no sign of big heat damage anywhere so my guess was that it has sustained some kind of physical shock during shipping or before.
    It turned out that other components were also failing so I took the whole unit apart

    It looks like a push-pull design. Mirroring the '80s eastern block shortage economy. Whatever parts were available in the market were used for design and production. Max output of this psu is about 150Watts.





    It has some EMI filtering.
    There are fuses socketed in series both on line and neutral:


    It has a decent fan that still spins super smooth:


    Inrush current limiter has several holes on it and measures 50-60 ohms. It's blown. It has color coding in the form of three dots:


    A foil capacitor was measured open and another 100nf+2x2.5nf X2Y wierdo type was 100-200ohms in one part:



    Main capacitors measure not so great and leakage current is high. Some audiophiles might think they look pretty cool though:


    The unit has a full bridge rectifier:


    Two IRF 740 FETs:


    Controlled by SG3526N. Supervisor is SG3543J:



    I couldn't take it apart without destroying the original heat transfer/insulator sheets.
    These sheets were all brittle and were falling apart:


    The main transformer is some high frequency core N27 material. I'm not an expert identyifing transformers so it took me some time until it was revealed
    to be EC41 type. My second guess was ETD core:


    It's still around and super cheap so I ordered some. The Epcos/TDK part goes by the name B66339G0000X127.


    Original main trafo with RC snubber hacked on it:



    The main board stripped down a bit:


    The secondary current stabilizer is also wound around a EC41 bobbin and N27 core material. It's glued together with some rtv silicone.


    Output diodes are schottky types for 5V and 12V rail. -5V is generated by 7905 regulator ic:


    There is no real low pass filter with inductors just electrolytic capacitors on the output filtering stage. Old Panasonic, Chemicon and random USSR caps are used. These all test ok.

    That's how far a I got now. I'll reassemble the main transformer and also might replace some old parts with matching nos parts. These "vintage" resistors, caps are still shoveled around since so much were made and some are still within specs.
    Attached Files

    #2
    Re: Videoton VT-110, XT clone PSU repair

    Reassambled the main trafo with the new cores:

    This time with some silicone too. Hopefully it's going to keep the bobbin and the cores from sliding around.

    Got several old electrolytic caps of the same brand but the parameters are kind of crap. These just won't do as replacement. I have to use modern parts.

    Also going to use real X2 and Y rated capacitors for the EMI stage.

    For the primary bulk these capacitors will be much better then the originals I think:


    I want to sacrifice as less authenticity as possible but that might not turn out to be safe enough.
    Attached Files

    Comment


      #3
      Re: Videoton VT-110, XT clone PSU repair

      Just noticed that most of pictures don't show up in the first post. I'll try to get it fixed.

      Comment


        #4
        Re: Videoton VT-110, XT clone PSU repair

        Attached the missing pictures of the internals/parts.
        I'll need to gather some minor parts like proper sized silicone heat transfer/insulation pads, small caps, spacers, etc. Probably going to reassamble and test the unit this weekend.
        Attached Files

        Comment


          #5
          Re: Videoton VT-110, XT clone PSU repair

          1. The input electrolytics were made by Roederstein.

          2. The date codes on the PWM and supervisor are 1988, "SG" being Silicon General, the creator of those ICs.

          3. However, the date code on the Matsushita fan is 1993

          4. It looks like that may be a half-bridge rather than a push-pull inverter, with TR2 providing gate drive.

          5. FT2 looks like it might be the output inductor. If it is and since its core is N27 ferrite the core is probably gapped, either with a spacer between the core halves or it is a machined pair. I'm pretty sure an ungapped ferrite core would saturate so that inductance would be minimal. Powdered iron cores are common in SMPS because they have an inherent distributed gap.

          6. IIRC, N27 ferrite is a fairly/very old material type, with multiple sources having equivalent materials. N27 was originally made by Siemens.

          7. Regarding ferrite cores generally, back when that power supply was made, the lead times for cores, unless they were in stock, tended to be awful. Core pairs with a machined gap - like that output inductor might be - tended to be made-to-order, even though they might be a catalog item, and the lead times could be on the order of a year. IIRC, in it's flyback designs, in which the main "transformer" core was gapped, Boschert used spacers to set the gap.
          Last edited by PeteS in CA; 06-28-2019, 11:41 AM.
          PeteS in CA

          Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
          ****************************
          To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
          ****************************

          Comment


            #6
            Re: Videoton VT-110, XT clone PSU repair

            Originally posted by PeteS in CA View Post
            3. However, the date code on the Matsushita fan is 1993
            The fan might not be the original after all. Maybe the psu was serviced before. All I know is that the Videoton PC production was halted in 1989.

            Originally posted by PeteS in CA View Post
            4. It looks like that may be a half-bridge rather than a push-pull inverter, with TR2 providing gate drive.
            You are correct. I've drawn back the and it is in fact half bridge configuration. The FETs are switched through TR2.

            Originally posted by PeteS in CA View Post
            5. FT2 looks like it might be the output inductor. If it is and since its core is N27 ferrite the core is probably gapped, either with a spacer between the core halves or it is a machined pair. I'm pretty sure an ungapped ferrite core would saturate so that inductance would be minimal. Powdered iron cores are common in SMPS because they have an inherent distributed gap.
            There are separators between the core halves on FT2 and it's bonded together with silicone.
            Attached Files

            Comment


              #7
              Re: Videoton VT-110, XT clone PSU repair

              Nice repair/restoration. Really great to see an old PSU like that brought back to life.

              If you need more AT PSUs let me know. I do have an old Astec that's built like a tank. Not sure if it works or not, but it's an Astec.

              Comment


                #8
                Re: Videoton VT-110, XT clone PSU repair

                Originally posted by momaka View Post
                Nice repair/restoration. Really great to see an old PSU like that brought back to life.
                Hey thanks! I'd really hate to see old historical stuff like this ending up on some e-waste pile. I also have some old Astec units. Even some server grade ones with APFC, from 1995!

                Managed to continue a bit with the repair.

                A tab from the heatsink goes under the main trafo. I speculate that if too much pressure is applied by the fastened screws the ferrite core might crack again. I put some thin insulation tape around that tab so it won't interface hard with the core.


                Taps coming out from the main trafo have damaged insulation. Seem to have flaked off at some points. I put heatshrink tubing over some of those wires so they won't short each other.


                All the new low voltage caps have higher temp and ripple current rating then the old ones. Physical size isn't a problem here thankfully. Plenty of room.


                The pcb has a spot for a fuse (B1) that was original jumped with a piece of wire since the unit has fuses elsewhere on the input. Maybe I could install a choke here for EMI filtering purposes.

                Also I noticed the the unit doesn't generate a Power Good output signal. The wiring is there but the trace just ends up in a via that goes nowhere!
                Could just wire it to 5V but I'm planning to install some 100ms delay circuit. Have to implement something since even the low end XT AT motherboards are picky about missing PG.

                The X2 caps I have won't fit between the other EMI parts like the original did. It has to stand away from the pcb a bit.


                I had to source some other parts and I'm still waiting stuff to arrive from farnell. I'm not in a hurry with this one anyway.
                Attached Files
                Last edited by pdavid; 07-08-2019, 06:40 AM.

                Comment


                  #9
                  Re: Videoton VT-110, XT clone PSU repair

                  Looks very good so far!

                  Originally posted by pdavid View Post
                  I also have some old Astec units. Even some server grade ones with APFC, from 1995!
                  And I bet they still work and haven't blown their primary cap, like some modern units do nowadays.

                  Originally posted by pdavid View Post
                  All the new low voltage caps have higher temp and ripple current rating then the old ones. Physical size isn't a problem here thankfully. Plenty of room.
                  https://www.badcaps.net/forum/attach...1&d=1562586210
                  That's the nice thing about old PSUs, isn't it - always have plenty of room for big caps.

                  Originally posted by pdavid View Post
                  Also I noticed the the unit doesn't generate a Power Good output signal. The wiring is there but the trace just ends up in a via that goes nowhere!
                  Could just wire it to 5V but I'm planning to install some 100ms delay circuit. Have to implement something since even the low end XT AT motherboards are picky about missing PG.
                  That's interesting.
                  Yes, certainly would be a good idea to make a circuit for PG. Shouldn't be too hard to implement anyways, even with basic parts (RC circuit, a comparator or shunt regulator of some sort, and maybe a transistor or two, I'm thinking.)

                  Originally posted by pdavid View Post
                  I had to source some other parts and I'm still waiting stuff to arrive from farnell. I'm not in a hurry with this one anyway.
                  Keep us updated.

                  Comment


                    #10
                    Re: Videoton VT-110, XT clone PSU repair

                    Originally posted by momaka View Post
                    Looks very good so far!


                    And I bet they still work and haven't blown their primary cap, like some modern units do nowadays.

                    Being Astec, that doesn't break hahahaha. Astec for me was the number 1 manufacturer in sources, and currently no manufacturer comes close to those great Astec designs.
                    I have several Astec, and they all work .
                    And one of them is from a Lenovo server with an ATX connector that I acquired on ebay, and I have had it running 6 months in a row.

                    I also want to see how the restoration progresses, that source looks great .
                    Last edited by kevin!; 08-11-2019, 06:37 AM.
                    Gaming pc:
                    nVidia RTX 3080 TI, Corsair RM750I.
                    Workshop PC:
                    Intel core i5 8400, Intel SSD 256GB, nvidia gt1030, asus b365-a.
                    Server:

                    Comment


                      #11
                      Re: Videoton VT-110, XT clone PSU repair

                      Recently I was quite busy with work, then taking a vacation and family and all
                      The motherboards I tested the PSU with generated their own power good signal and worked just fine.

                      I'm planing to make some simple power good circuit though...
                      Some other AT unit has it like this:

                      Probably going to etch a board and use smd components. Good enough.
                      Attached Files

                      Comment


                        #12
                        Re: Videoton VT-110, XT clone PSU repair

                        ^ I like it. Very basic delay circuit (RC low-pass driving a transistor), but it should work fine.

                        Comment

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