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Repairing Old School Power Supply?

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  • #46
    My vote is a tapped secondary.

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    • #47
      There is another possibility. Since there are 2 secondary coils, they can be separated from each other and the wire of the last coat of winding can be stripped from the enamel insulation just like a variac. Now to complete the circuit, the wiper can bridge the 2 coils, keeping the ratio of the 2 windings constant. If you remove the wiper, you open the circuit and it stops working
      Helder Ferreira
      Setubal, Portugal

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      • #48
        Crap-o-cad drawing with wiper in yellow or red position
        You may only view thumbnails in this gallery. This gallery has 1 photos.
        Helder Ferreira
        Setubal, Portugal

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        • #49
          In my second picture you can see a rectangular sort of thing behind the transformer which is connected to the knob on the front. Just this side of that is a contact that moves with the knob along contacts on the backside of the transformer or what might be called a rheostat, variable resistor or variac - I am not at all electrically inclined so I don't know the correct term.

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          • #50
            It's a variable tapped secondary.

            First thing to do is to put a voltmeter on the yellow wires (one lead on each). Is there any voltage? If so, does the voltage change when you vary the front knob?

            My first pass guess is that one or both of your diodes is bad and will need replacing. Also, as bad as the outside of the case was with rust, there is a possibility that the transformer core has rusted out. If so, then send it to the trash.

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            • #51
              Noitoen's last drawing is most likely correct. That is a split secondary adjustable transformer. They are not common, but they were used in higher current low voltage adjustable AC voltage systems. I have seen them used in very high power transmitters for adjusting the filament voltage for the LARGE tubes. In any case I see many possible issues in the pictures. There are several very poor solder connections. One on the power switch looks like it may not even be making contact. With the rust/corrosion I would also be suspect of the movable secondary shorting bar contact with the transformer. Same for the power switch. The circuit is very simple, but if you have no electronic/electrical experience you need to find someone to help. Look around your area for older radio and TV repair shops. Another good source for help would be local amateur radio (Ham Radio) operators. Simple voltage measurements will tell the story, but for safety sake I will not attempt to tell you what to do. Sorry...
              Robin

              Happily working on my second million Gave up on the first

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              • #52
                Originally posted by The Artful Bodger View Post
                So that is interesting, just what does the knob on the front panel do? It looks like there is some sort of swinging arm so maybe contacts on the secondary, or is something happening in the magnetic circuit?
                Just as I suggested, and Noitoen drew. It's a fonky variac, but it is one. Yes, tapped secondary..... a variac just has a LOT of taps.

                Taps may go to ground, that would be mechanically simple to implement. but is functionally identical to having them more directly in series with the rectifiers. Primary presumably wound under each secondary.

                Very simple setup, low voltage, one rectifier cell each side. Cells see double the peak voltage, so presumably that is under 12V by jut enough.
                CNC machines only go through the motions

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                • #53
                  It could be a variable magnetic shunt transformer, where the coupling between primary and secondary is adjusted by a moving iron yoke, or shunt. Similar to the following:

                  https://nationalmaglab.org/education...magnetic-shunt

                  Click image for larger version

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                  https://patents.google.com/patent/US3622868A/en

                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

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                  • #54
                    Thanks for that, Paul. It's a neat concept. I'd had something similar going through my head for the power supply but couldn't quite put it together. I'm NOT an EE!
                    Southwest Utah

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                    • #55
                      Those have been used in welders, and in automatic regulators for street lighting. I don't think this one is that fancy.... the layout of the magnetic circuit is just wrong-appearing for it.


                      A [ic more straight down on the front part of it would show for sure.
                      CNC machines only go through the motions

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                      • #56
                        Originally posted by PStechPaul View Post
                        It could be a variable magnetic shunt transformer, where the coupling between primary and secondary is adjusted by a moving iron yoke, or shunt. Similar to the following:

                        https://nationalmaglab.org/education...magnetic-shunt

                        Click image for larger version

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                        Click image for larger version

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                        https://patents.google.com/patent/US3622868A/en
                        Those regulate the current and not the voltage. You will only see the voltage change under load
                        Helder Ferreira
                        Setubal, Portugal

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                        • #57
                          There is no sign of overheat on the transformer so, with the exception of those rectifier bolts, everything could be disassembled and cleaned to restore good contact between the connections.
                          Helder Ferreira
                          Setubal, Portugal

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                          • #58
                            Can't believe I just saw it now- that transformer IS the variac. I was wondering why it was mounted so close to the front panel- now it makes sense.

                            Here's a nugget from my past experience which I just thought of- I had a unit in one day which wouldn't power up. The fuse checked ok, power cord ok, plug ok, and power switch ok. No power to the transformer. In this case the fuse holder wasn't passing the juice. A little unusual, but it happens. Fast track the troubleshooting and see if the transformer energizes before you get too deep into the wiring.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #59
                              Originally posted by Dave C View Post
                              All this discussion of selenium rectifiers has got me worried about my mig welder's health. I has a big (4") square selenium rectifier in it and it has been replaced once.
                              Miller makes a generic drop in replacement rectifier that you can fit in there somehow. It's in their general parts catalog.

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                              • #60
                                Did a quick search online and that same power supply is quite common under different brands. Gesswein Electro Plater model D

                                30a jóias ouro prata chapeamento máquina, galvanoplastia máquina, galvanoplastia retificador, ródio chapeamento máquina de revestimento,Aproveite promoções, envio grátis, proteção ao consumidor e retorno simplificado ao comprar de lojas na China e no mundo inteiro! Aproveite ✓Envio gratuito para todo o mundo! ✓Promoções de tempo limitado ✓Devoluções fáceis
                                Helder Ferreira
                                Setubal, Portugal

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