Electrical Problem - Any Suggestions?

Discussion in 'FAQs' started by bigdonnie, Nov 29, 2004.

  1. bigdonnie

    bigdonnie Member

    I've run into a very strange problem with the wiring of my coffee table layout control panel that maybe someone in the group can help me troubleshoot.

    I decided to use 25 pin connectors in the control panel and at the layout facia so that I will be able to hookup/unhook everything quickly and store it away in a drawer of the table itself when the layout's not in use.

    Over the weekend I was able to get all of the connections soldered for the power feeds to the layout. There are four sets of feeders --- one for the main, one for the reversing loops (there are 3 reverse loops) and two for the yards (I wanted to be able to have additional locos waiting in the yards while one was running on the main line).

    OK, here's my problem and what I've trouble shooted so far. When I check the four feeders with a multimeter at the panel connector everything seems great --- same voltage across each set (which tells me I've wired the 4 DPDT switches on the panel properly). However, when I check the voltages at the 25 pin connector on the layout side, I'm only showing power to the main, not to the other three. I've tried different conecting cords on the basis that that could be the problem, but in every case I am only getting power across to the main.

    Any suggestions as to what I should be checking next?
  2. moria

    moria Member

    Hi Donnie :)

    Very odd :)

    heres the two things I would check first..

    1) Are the connecting cables you are using actually wired on all 25 pins straight through with none missing and none reversed.

    Its possible to buy 25 way cables for computers that either a) don't have all pins connected (serial port cables) or even have some pins reversed.. ie pin2 goes to pin 24.

    2) When you soldered the socket at the control panel end.. did the temperature get up high enough that the socket has loosened the connectors so they have been pushed out of alignment and are not making contact with the pins of the cable?


    Graham Evans
  3. Fred_M

    Fred_M Guest

    Also note that on DB25 cables several of the pins are common grounds and some cable makers bundle the grounds into one wire in the cable to save money. Pins 18-25 are bonded this way as a rule. Also some older cables didn't even bother to common bond the grounds and left some of them unattached. Google DB25 pinouts or look here for guiadance. http://www.bcar.us/Common Cable Pinout Information.htm Fred
  4. bigdonnie

    bigdonnie Member


    Thanks for the suggestions. I'll check the cables tonight and see where that takes me.

    One other question --- is there a better option than 25 pin connectors/cables? I went with this approach because it theoretically will meet my objective of fast'easy setup, but the electrical/electronic side of our hobby is definitely NOT one of my strengths.
  5. moria

    moria Member

    Hi :)

    25 way is a good way to go. Always carry a couple of spare cables in case of bent pins or other troubles :) 25 way are, to my mind, the best compromise between number of wires available in one plug/socket and ease of soldering wires into them.

    Did a layout once with 50 way connectors, and soldering the wires into the middle row of pins was hell :)


  6. bigdonnie

    bigdonnie Member

    Thanks Graham --- its reassuring to know I haven't been going down a path that I shouldn't have been on in the first place :)

    BTW --- I thought about the 50 way connector as well because I have a total of 62 connections to do, now I'm glad I didn't go that route. Even the 25 way are finicky enough --- the first row is relatively easy, but then you need to flip it over to do the second and that's somewhat of a pain! However, like most things, you develop a technique that works for you and its not too bad. I have been using this new 'Cold Heat' soldering tool and that has really helped make the job easier.

    Thanks again
  7. bigdonnie

    bigdonnie Member


    Thanks for pointing out this web site to me. One quick about question --- if a 25 pin serial port and cable only has 9 operable pins, why would you not just go with a 9 pin serial port and cable?

    Probably a stupid question --- what am I missing?
  8. theBear

    theBear Member

    Actually very few wires are needed (ground, transmit, and recieve) for rs232 the "normal" use of the DB25 cables. At one time you took your life in your hands playing with a "rs232" connector that was plugged into a device. There used to be all kinds of things done with the "spare" wires including running line voltage [​IMG][​IMG][​IMG] [​IMG][​IMG].
  9. bigdonnie

    bigdonnie Member


    FYI --- I checked the cables when I got home and suffice it to say that I felt a tad foolish when I discovered that they were null modem --- oops! :oops: Equally useless to me as serial since only 9 pins end up being connected (plus reversed for reasons that escape me)

    Moral of the story --- always do all of your homework ahead of time. Thank goodness I bought the cables for only $6 CDN each at a surplus electronics place ;)

    Anybody need 3 slightly used null modem cables? :)

    Thanks very much for pointing me to the root cause of my problem.
  10. theBear

    theBear Member

    What you need is a full 25 conductor straight through rs232 cable.

    Radio Shack used to sell these, maybe they still do.

    Do you have a Best Buy handy they sell a number of cables for computers.

    A null modem replaces a real modem by routing the send wire to the receive pin on one end and the receive wire to the send pin on the other because it replaces the equipment that in effect did that.
  11. Fred_M

    Fred_M Guest

    DB25 standards predated DB9 cabeling. DB25 cables had secondary data paths for reliabilty back in the days. That's speaking about straight through RS232 cables. But just because it has a DB 25 on each end don't make it a serial (rs232) cable as you found. There are several standard ways to configure DB25 cables. http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html SCSI external devices even used BD25 ends on the cables back years ago. You need a DB25 25 conductor straight through cable to make you gizmo work, which can be had. Fred

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