Connect with us

unijunction needed

Discussion in 'Electronic Components' started by alp soandso, Sep 23, 2011.

Scroll to continue with content
  1. alp soandso

    alp soandso Guest

    Looking for a part made by ssi.

    MSU 112-2

    I need one. Will a few more if absolutely necessary and price is low. Not
    looking to buy $200 minimum.

    I live in Canada.

    you can contact me by email by removing the first alp in the address.
  2. Jamie

    Jamie Guest

    I can't seem to find a spec on that part? Maybe if you knew some more
    information on it, like the Peak Voltage, valley etc on the emitter one
    could be dropped in.

    I have some unijunctions in my drawers and as far as know, they didn't
    make to many different types.

  3. alp soandso

    alp soandso Guest

    I don't know anything about the device. I have a delay timer/relay that
    is supposed to activate a cryogenic compressor after a roughing pump has
    run for about one minute. It suddenly stopped working. I opened the timer/

    It is a Potter Brumfield CUF-41-30120.

    It has very few components wired up between 8 contacts or so. I have
    replaced the capacitors (two of them) and the diode checked out fine, but
    I put a new one in anyway. The resistors look fine, I have not tested
    them yet nor did I plan to. I believe the coil is fine, but I will have
    to unsolder a few parts to make sure I am not reading this wrong. The
    prime suspect right now is the MSU 112-2, which I have been told is a
    UJT, perhaps a PUJT (PUT). I wouldn't know where or how to measure the
    peak voltages/current..... I would be poking around inside a relay with
    240 v and several amps behind it. Not something I want to do with the
    part installed on the device and the device running.

    Ian, thanks for the links. If I study hard and long enough I will be
    able to come up with a replacement of my own manufacture. I doubt I have
    long enough to live however (I joke, but in reality my capacity to learn
    new stuff has dropped off significantly over the last couple of years).
    They should at least get me pointed in the right direction if I have to
    try (and don't wish to pay the 200-300 bucks for a new timer/relay).


  4. Jamie

    Jamie Guest


  5. alp soandso

    alp soandso Guest

    On Tue, 27 Sep 2011 14:14:00 -0500, Jon Elson wrote:

    Yes, Jamie is correct, the cost of the device is ridiculous.

    I would be able to build something (hack) if I could figure out how this
    circuit works. With all the pdf links I got from the other newsgroup
    posting I should be able to figure something out.

    Thanks again
  6. ehsjr

    ehsjr Guest

    Yep, >$200 is horrible. If you know the function(s) the relay
    must deliver, you can build a circuit to do it using current

    Some issues to determine concerning the function(s):
    You say that the relay must operate after the roughing pump
    has run for about 1 minute.

    * What is the relay supposed to do if the roughing pump runs for
    less than 1 minute?
    * Once the relay activates, how/when is it supposed to de-activate?
    * How much current at what voltage must the relay switch?
    * How many poles must the relay switch?

    If you have room in the machine, and are willing to re-wire a bit
    if necessary, delivering the functions you need with an external
    circuit is a piece of cake, provided of course that you know those
    functions. OTOH, if you must create a drop-in replacement for (or
    repair of) the bad part, that can be a PITA.

  7. alp soandso

    alp soandso Guest

    Thanks for taking the effort to explain. I managed to download a bunch of
    files explaining this sort of thing as well, but my main background is
    chemistry, not electronics. I know what the words mean, but they don't
    make much sense right now.
    Maybe I'll get lucky and find out it was the tantalum capacitor that went

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day