Announcement

Collapse
No announcement yet.

Signal Stat 900 Pilot Light on a Positive Ground System

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Electrical: Signal Stat 900 Pilot Light on a Positive Ground System

    I have a Signal Stat 900 turn signal/emergency signal unit installed in my 1948 M15A-20 6-volt positive ground truck and the "Pilot" lamp does not light. I opened up the flasher unit (type 535) and discovered that there is a three terminal solid state device connected to the "P" terminal (Pilot). The device is probably a PNP transistor FET that makes it polarity sensitive. I changed the polarity of the battery (stand-alone circuit using a battery charger) and it works fine. It appears that the 535 flasher is intended for a negative ground system not a positive ground system.

    Does anybody know of a positive ground three terminal flasher?
    1948 M15A-20 Flatbed Truck Rescue
    See rescue progress here on this blog:
    http://studem15a-20.blogspot.com/

  • #2
    Try reversing the power and ground feeds to the flasher? If that is a non-starter you can always flip the transistor leads. My flasher worked right out of the box but it is ancient and probably totally mechanical inside. I don't know what the part number was but I can probably read it off there tonight if that would help.

    Nathan
    _______________
    http://stude.vonadatech.com
    https://jeepster.vonadatech.com

    Comment


    • #3
      Originally posted by JohnM15 View Post
      I have a Signal Stat 900 turn signal/emergency signal unit installed in my 1948 M15A-20 6-volt positive ground truck and the "Pilot" lamp does not light. I opened up the flasher unit (type 535) and discovered that there is a three terminal solid state device connected to the "P" terminal (Pilot). The device is probably a PNP transistor FET that makes it polarity sensitive. I changed the polarity of the battery (stand-alone circuit using a battery charger) and it works fine. It appears that the 535 flasher is intended for a negative ground system not a positive ground system.

      Does anybody know of a positive ground three terminal flasher?
      SO THAT 'SPLAINS IT!!!

      I too have installed an aftermarket turn signal kit on a 6 volt positive ground vehicle with similar results. My pilot light will flash once or twice and fade away. I have checked the actual turn signal lights and they operate as they should, so I am not so bothered by the little blinker inside not blaring away. My system was set up for twelve volts but I merely changed the bulbs and wired it per the instructions.


      Thanks for posting this because it lets others know that the condition is not uncommon. I know enough electrical and electronic stuff to get myself into trouble, but sometimes, not enough to get out of trouble.

      I have another older unit I installed in my '48 coupe and it works OK. Years ago, I was in one of those little southern mill towns where the mill had closed and most of the businesses were fading away. I wandered into a former Western Auto Store that had pretty much dwindled into an antique/flea market store. As usual, I engaged the owner in a conversation and when I brought up the subject of Studebaker, he came up with the old turn signal set and just gave it to me. The application on the box said Studebaker and he said he didn't think he would ever run into anyone who would have a use for it. Any way, that one works fine and I guess that the more modern ones have some components that are not so friendly with the old positive ground systems.
      John Clary
      Greer, SC

      SDC member since 1975

      Comment


      • #4
        Here is what I have figured out. Have not tried changing the transistor yet:



        1948 M15A-20 Flatbed Truck Rescue
        See rescue progress here on this blog:
        http://studem15a-20.blogspot.com/

        Comment


        • #5
          Oops, forgot the theory of operation:

          Power is applied to the "X" terminal. Signal switches are off, therefore there is no current draw through the "L" terminal and it remains at the battery potential. Since there is no current draw out the "L" terminal, there is no potential developed across the bi-metal heater causing the transistor to be in the off state. When the transistor is in the off state, there is no current flow out the "P" terminal, thus, the pilot lamp is off.

          When the signal switch is on, current flows out the "L" terminal and the bi-metal heater has the battery potential across it because the signal lamps have a lower resistance than the bi-metal heater. At this time the transistor senses this battery potential across it's base to emitter junction and turns on the transistor, causing the pilot lamp to energize.

          When the bi-metal heater heats up the bi-metal enough for the contacts to close, the heater is de-energized, the signal lamps now energize, and the transistor is turned off causing the pilot lamp to de-energize.

          When the bi-metal cools, the contacts open and the cycle repeats as long as there is a load on the "L" terminal (signal switch turned on).
          1948 M15A-20 Flatbed Truck Rescue
          See rescue progress here on this blog:
          http://studem15a-20.blogspot.com/

          Comment


          • #6
            Transistor Sister!

            All that technical stuff is well and good (I guess), but didn't you forget something else?

            According to this, don't you have to replace the C9012 PNP Transistor with a 2N2222 NPN Transistor?

            And what is that, and where do you get it?

            Comment


            • #7
              John, I think you have nailed it. It agrees with what little I know of transistor theory, anyway.

              One thing that I can guarantee you will work, is to replace the pilot lamp socket with a non-grounded one, and simply connect one terminal to the wire going to the left front signal lamp, and the other to the wire going to the right front signal lamp. In operation, the pilot lamp "sees hot" from the lamp that is being flashed, and "sees ground" from the non-flashed one. The pilot lamp filament does not draw enough juice to illuminate the non-flashed lamp, not even a little bit.

              If you used polarity-sensitive lamps, like LEDs, this way, you could even get left and right telltales.
              Gord Richmond, within Weasel range of the Alberta Badlands

              Comment


              • #8
                Where to find the 2N2222 transistor, at least one of the places......

                http://www.radioshack.com/product/in...ductId=2062586


                Don't laugh too hard, and yeah the place here still stocks the little stuff like this . It's a typical amplifying transistor. I'm not up on transistor logic, but the transistor was flipped from PNP(Positive-Negative-Positive) to NPN(Negative-Positive-Negative) to account for the change in battery polarity.

                Digikey also stocks the transistors as well:

                http://parts.digikey.com/1/parts/100...18-2n2222.html
                1964 Studebaker Commander R2 clone
                1963 Studebaker Daytona Hardtop with no engine or transmission
                1950 Studebaker 2R5 w/170 six cylinder and 3spd OD
                1955 Studebaker Commander Hardtop w/289 and 3spd OD and Megasquirt port fuel injection(among other things)

                Comment


                • #9
                  Sorry for the technical stuff but I've been an electrical engineer all my life (retired now) and am not used to talking to non-technical folks

                  2N2222 is a very common transistor and this circuit is not very challenging for it. What is really needed is a transistor that is NPN, have a collector current of 500 ma. or greater and some gain (Hfe of ~50). Bandwidth is of no consequence... The key here is the collector current. It must handle the pilot lamp current...

                  I'll go to my junk box and find a 2N2222 to test. Will post some pics.
                  1948 M15A-20 Flatbed Truck Rescue
                  See rescue progress here on this blog:
                  http://studem15a-20.blogspot.com/

                  Comment


                  • #10
                    I think this is the datasheet for the original PNP part.

                    http://www.keccorp.com/data/databook...ng/KTC9012.pdf

                    Can't say I have heard of KEC semiconductor before. Likely they sell to asian consumer electronics OEM mfgrs only. I did try 2SC9012 since most all japanese discretes like this are 2Sxxxx parts. I found this one indirectly from cross reference on the Toshiba website.

                    The 2N2222 or more easily found PN2222a should likely work OK as a "dual" to the C9012 part. The 2N2222 was the old metal can package part and I am not sure they make them anymore so could be hard to find. The PN2222a is the modern equivelent in a plastic package. Can be found from digikey or other suppliers but you probably need to buy a barrel of them...

                    One thing that confused me a moment on the otherwise very nicely done schematic until I looked closer was the battery symbol was upside down for the positive ground version on the bottom. You marked the polarity fine but the convention for battery symbols is the short lines are the negative plates of the battery and the long lines are the positive. So to be completely correct, the battery symbol should be flipped over.

                    Jeff in ND

                    Comment


                    • #11
                      Jeff_H,

                      You be right on the battery symbol. Most folks don't notice the difference.

                      Here are some pics:

                      The flasher opened up:


                      Close up of the flasher:


                      The 2N2222A that I found in my junk box removed from a DIP carrier (short leads...)


                      The 2N2222A installed:


                      I tested the modification and it works great!

                      Probably shoud mark the outside of the flasher that it was modified and put a note inside the can...
                      1948 M15A-20 Flatbed Truck Rescue
                      See rescue progress here on this blog:
                      http://studem15a-20.blogspot.com/

                      Comment


                      • #12
                        I fixed the battery symbol...
                        1948 M15A-20 Flatbed Truck Rescue
                        See rescue progress here on this blog:
                        http://studem15a-20.blogspot.com/

                        Comment

                        Working...
                        X