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Old Electronics Parts & Diagrams

Discussion in 'Datasheets, Manuals and Component Identification' started by Brandyn, Jan 26, 2016.

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  1. Brandyn


    Jan 17, 2016
    I am working on an old desktop power supply unit. There are no PCB's and I thought the best way to start repairing it would be to build a wiring diagram. While working on it I found three transformer pairs tied together in a manner which I am unaccustomed.

    I have attached our images of one of the pairs.

    The large transformer is wired as you would expect. There are two winding, one with a 120vAC current, the other the output. (Given that I do not know how they are wired and if they even work I have not attached power to them yet as I would like to have an idea of how they operate before testing if possible.) The top transformer however has only one set out wires leading out of it and as best I can tell only a single winding. I could be wrong about the number of windings but I am reluctant to try tearing into it to find out in the event I can not get a replacement.

    What I'm really hoping to find out is what principal these are operating on, with only two leads obvious the only other place for a secondary set of connections to the smaller transformer is under the (soldered?) legs. But the heat from the soldering would likely cause the insulation on a wire to melt and create a short with the housing and the case. The large transformer is bolted to the external housing which is metal and non-insulated. Therefore there is no way 120v could be presented here.

    I have a few thoughts, some of which are strange. The first is that it is using an insulator which could withstand the heat that I am unaware of. (Most likely, but then why are the two units connected together instead of left apart and wired more conventionally?)

    The second is that it could be the output of the large trasnformer is small enough that it is trasnfered to the small trasnformer through the casing, which is rendered safe by the case gound (This does not make sense to me but I may be missing something?)

    The third is that the top element is not a transformer at all, but an induction coil used to vary the inducatance of the large transformer and change the output voltage by inducing a current controlled by a variable potentiometer on the unit. (I don't know enough to see that this would be possible or impossible, but it is an idea that someone with my amount of knowledge (Just enough to be dangerous) might try.)

    The fourth, which just occured to me, is that it is some sort of method to trasnfer the indcutance of the coil and reverse it so that a steady DC output could be trasnfered from the AC Input of a transformer. This seems wildly impossible, but thinking about it I wanted to put it into words so I could look at the wiring on the outputs of both transformers and see if they meet back up anywhere to achieve something like this.

    Or I could be missing something entirely, which is why I'm asking here before I try anything crazy.

    I gave the part numbers and information on the part to a technician at Digikeys and she was not able to figure out what it is or if they had a replacement available. So until I get some idea of what they are I am hesistant to try putting too much time into repairing or diagramming a device that I may never get to function correctly because of these odd little things.

    Attached Files:

    Last edited by a moderator: Jan 26, 2016
  2. Bluejets


    Oct 5, 2014
    Maybe just a choke on the DC side.
    Hard to say, difficult see any connections.
    Bit of a rats nest really.
    davenn likes this.
  3. Brandyn


    Jan 17, 2016
    It is. The small transformer (if that's what it is) is has two leads off the side of it. I'll try taking some better pictures and get a better idea of what the transformers lead to and add an update shortly. I will cut one out of the curcuit to get better pictures.
  4. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Brandyn . . . . .

    The way that I am seeing it, is that none of the magical and mystical feats that you mentioned are being involved.
    The main power transformer is being the one on the bottom.
    If using, and having, only two leads on the upper stacked smaller transformer it must be used in an old school design, series filter in the power supply, in between two main electrolytic filters.

    ( It certainly took one HEFTY . . .elevated by the power of 10 . . .soldering iron, in order to join those top tabs to the lower wrap around on the power transformers. )

    The bottom transformer seems normal and a purchased buy, while the top one probably was scavenged.
    Over to the perf board construction area, there are seen, TWO black FWB potted rectifier units . . . but being marginally power sized . . . in respect to the main transformers specs.

    Give us some good clear close up photos of the component side of the perf board, along with a shot of its rats nest wiring side and we will see what can be ascertained as to its design.

    73's de Edd
    Last edited by a moderator: Jan 27, 2016
  5. Brandyn


    Jan 17, 2016
    73 de Edd,

    Thanks for your reply. I am glad that my wild thinking was wildly off. I've been thinking the part over for several days and my imagination was probably getting the better of me haha.

    I've never heard of a series filter, I will have to look that up when I get home.

    The supply unit has four variable voltage outputs. But only 3 of these transformer pairs. That's why I'm trying to understand what they are, and why I decided it would be best by starting with making a circuit diagram before I started taking it apart to repair it.

    I'll upload more pictures when I get home as well.

    Your mentioning that the top trasnformers seem to be scavenged makes me think. I have an identical (on the outside) supply in storage. I will get it out and see if it has the same components, or if they are very different.


    I am sorry, I forgot to thank you for your reply earlier. So thank you.
  6. Bluejets


    Oct 5, 2014
    In the old style power supplies, capacitors were used to smooth the ripple on the voltage and the series filter (choke) is for smoothing the ripple on the current.

    In old valve radios, they (choke / series filter)served a dual purpose.
    That mentioned above and also to create a magnetic field for the speaker and hence were mounted on the speaker.
    Brandyn likes this.
  7. duke37


    Jan 9, 2011
    If the top 'transformer' is in fact a choke, it will have two leads only.

    I do not like the look of the black blob on it, check to see if there is a connection through it. You will need to disconnect one wire to do this.

    I see no problem with heat and soldering, the lugs are far away from any wires should you wish to remove the top inductance and you could disconnect at the board end to do a measurement.
  8. HellasTechn


    Apr 14, 2013
    What do you mean no pcb's ?
  9. Brandyn


    Jan 17, 2016
    There are no printed circuit boards. There is an old style of board, it kind of looks like an old peg board but smaller, that a few of the components are mounted to with leads soldered to a medium guage of wire. Hence the rats nest appearance. You can actually see the only board in the unit there in the left of the first image.

    I didn't like the black blob either, thats I'm i'm thinking all three pairs need replaced, they all have similar discoloration. The unit outputs ~0.5v above the readings on the meter / what it is supposed to be set to.

    i have not had time to take more pictures of this unit. However I will get them taken, and the part taken out and tested, tonight.
  10. dorke


    Jun 20, 2015
    What kind of Desktop is it?
    What you describe is probably not an original power supply,
    some kind of improvisation/replacement .
    No one builds a commercial product this way!
  11. Brandyn


    Jan 17, 2016
    It is an old analog switching power supply for electronics testing.
    The housing says PTS Electronics (Which was an electronics repair shop in Indiana)
    I'd say they custom build, or had it custom built when it was new and repaired it when it needed repaired.
    It has 4 leads with knobs (variable pots I'm thinking?) for voltage control 5-30vDC


    I've not had time to take more pics yet, but will get them posted ASAP. I really appreciate everyone's input on this, I'm sorry for not being able to be more on the ball with the pictures things are being hectic this week.
  12. dorke


    Jun 20, 2015
    I see now, I thought by "desktop" you meant a desktop PC.
    What do you intend to use it for?
    A "Variable Lab power supply"?
    What are the needed Voltage(s) and current(s)?
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