Connect with us

Please help identify this variable resistor

Discussion in 'General Electronics Discussion' started by hotrodjohn71, Jul 22, 2017.

Scroll to continue with content
  1. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
    Hi guys, thanks for permission to this forum. If my question is asked in the wrong section, please advise and I will correct.
    I am trying to find a match to a potentiometer I removed from an old Montogomery Wards Record player. I think from my research it is called a linear PC mount style as it solders right into a circut board. The printing on the component itself says : T2. c38-046 A 10K ohms .

    I want to google search for the closest one I can find to install but am not coming up with much.
     

    Attached Files:

  2. hevans1944

    hevans1944 Hop - AC8NS

    4,541
    2,116
    Jun 21, 2012
    Since it came out of a record player, I would bet dollars to donuts that it is an audio taper instead of a linear taper potentiometer. Try this one on for size.
     
    hotrodjohn71 likes this.
  3. Minder

    Minder

    3,013
    640
    Apr 24, 2015
    I second that, if it used for volume control then usually Logarithmic version.
    M.
     
    hotrodjohn71 likes this.
  4. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
    Hi Heavens1944, thank you for your reply. The potentiometer didnt actually come from the record player part of the unit, but this MontgomeryWard recordplayer has a seperate unit within the console that takes sound pulses from the speaker wires and runs it through a device that causes these multi colored lights to flash that are in the console depending on intensity and volume of the music (a 1970's thing.....) So the potentiometer Im looking for goes with that light setup and governs the 'intensity' of the flashing on that circuit, so not necessarily an audio adjustment, but a type of intensity adjustment for the bulbs which are 110v bulbs (like old fashioned outdoor Christmas light bulbs), or perhaps maybe an intensity adjustment for the inputted sound signal from the speaker wires.

    The light flasher unit does have 2 of these identical potentiometers. one for a channel A and one for a channel B, so I have one good one I can test to help verify it but am not sure how I would do that.
     
    Last edited: Jul 22, 2017
  5. Minder

    Minder

    3,013
    640
    Apr 24, 2015
    So most likely a Triac unit or other , which in that case would more likely to be linear.
    Try Digikey, they usually come through for me.
    M.
     
    hotrodjohn71 likes this.
  6. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    The mounting is less important than the shape and size of the shaft the knob sits on.

    Any suitable 10k pot can be fitted and wires connected to solder to the board but if the collar and shaft shape/diameter aren't correct then you won't (possibly) get the control knob to refit.

    That shaft indicates a push-fit knob.

    Potentiometers are also 'classified' by their body diameter - what does yours measure?

    Anyway, eBay has a load of different pcb-mount pots and a typical example that may fit is as follows

    http://www.ebay.co.uk/itm/PCB-Strai...hash=item1a1720674f:m:mDNXtJEE4JSCGM_q-aGTxtA
     
    hotrodjohn71 likes this.
  7. Minder

    Minder

    3,013
    640
    Apr 24, 2015
    What I like about Digikey, the part is at my door the following day,
    The other thing to consider if there is a possibility of the pot being part of a AC mains circuit is to ensure that the pot has a plastic shaft, as does the original.
    M.
     
    hotrodjohn71 likes this.
  8. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
    Thank you guys for giving me alot to go by. Would there be a noticable difference between the logarithmic version and the linear? Great info! I really appreciate it!
    Didgikey has about 700 different units to choose from. Which wattage do you think might be sufficient as there are many different options?

    Usually when I research an item like this for replacement as I am with this, if there is a part # available like there is with this one, I can usually google it and find a spreadsheet of its specifics and then locate a suitable match, but with this particular potentiometer, there is absolutely no Google match.
     

    Attached Files:

    Last edited: Jul 22, 2017
  9. Minder

    Minder

    3,013
    640
    Apr 24, 2015
    If it is used in the type of circuit I think it is the wattage is not required to be that high, usually a simple timing circuit.
    If it has a carbon or similar track then it will be low w.
    For the same reason I believe it will be linear.
    Log type you will not get the predictable response that you get with the linear.
    M.
     
    hotrodjohn71 likes this.
  10. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    hotrodjohn71 likes this.
  11. dorke

    dorke

    2,342
    665
    Jun 20, 2015

    This gadget was once called "a light organ" (like a John Travolta disco dancing floor).
    Since as you say it is from the 70's the writing on the pot "A 10K",means a 10K linear potentiometer.

    Why do you need to replace it?
    Did you try spray it with Deoxit?
     
    hotrodjohn71 likes this.
  12. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
    Hi dorke, you are exactly precisely correct! The unit iI'm working on is the top one in the photo. It has been my wife's from childhood. Recently we were in an antique store and she saw that Chipmunks Christmas record. I secretly got it and thought I'd give it to her for Christmas and secretly restore her record player to play it on. I did get a can of that contact cleaner/lubricant for the volume, balance and tone potentiometers because they are crackley, but that one I am enquiring about in this thread was sparking inside and catching internally and not working. Being curious, I carefully opened it up (after removing it from the circuit board) by prying the little fingers, but if appeares to be partially melted inside.
     

    Attached Files:

    • raw.jpeg
      raw.jpeg
      File size:
      112.1 KB
      Views:
      94
  13. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
  14. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Looks fine.

    You should measure the mechanical dimensions of the one you have and compare them to the datasheet of the potentiometer here.

    Especially the 5 pins (2 mechanical) distance and diameter.
    The shaft length,diameter and style(teeth number).
    The one you chose is 10K linear,single, with 18-teeth shaft 25mm long.
     
    Last edited: Jul 23, 2017
    hotrodjohn71 likes this.
  15. Minder

    Minder

    3,013
    640
    Apr 24, 2015
    Also the mounting 'ears' can often be adjusted slightly to take care of different mounting dims.
    M..
     
    hotrodjohn71 likes this.
  16. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
    Thank you.
    Is there a term for the orientation of the pins and ears? I just noticed that that unit at Digikey has the pins and ears going the opposite direction.
     

    Attached Files:

  17. Minder

    Minder

    3,013
    640
    Apr 24, 2015
    It refers to the mounting 'ears' on each side that has some leeway usually for spacing adjstment.
    M.
     
    hotrodjohn71 likes this.
  18. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Yes there is a term:
    Yours is called "rear adjust" the Digikey one above is "top adjust".

    This one has this option.
    Looks different dimensions and ears,may be you could improvise with it.
     
    hotrodjohn71 likes this.
  19. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
    Thank you all for the help in sourcing a potentiometer.
    I got one installed. I plugged everything in and the new potentiometer sparked and got smoked. So now i know the problem isnt the potentiometer but just a symptom of something bigger.
    Please give an opinion: This unit I'm working on here is for controlling the flashing of 5 watt -120volt multi colored bulbs (c7 colored night light style bulbs) .

    This light flasher unit runs 2 lines of (4) light bulbs each in the console of this montgomery ward entertainment center.

    One line is called channel 1 and one line is called channel 2. So that it has 2 light strings that do the same thing but probably flash at slightly different times. Each line has its own potentiometer to control light intensity.

    This light flasher setup gets its signal from a pink and white wire that connect to the nearest speaker. This flasher unit is totally seperate from the stereo , tape, phonograph and everything else except for the speaker wire signal.

    Also, in this unit is a power supply plug for the stereo setup. So this flasher unit plugs into the wall, then has 4 outlets on it.

    One of the 4 plugs is for power supply to the stereo which is always on as long as the plug is in the wall. 2 of the 4 outlets are channel 1 and channel 2 for the flashing colored lights, and one outlet is simply an outlet with a switch for auxillary lights for the 'post' which this unit never came with.

    One channel, channel 2, does work and does flash the colored lights according to the speaker signal input, but as soon as I plug in the light string to the channel 1 plug on the flasher unit, I see bad sparking in the potentiometer and some smoke. That potentiometer (the one I just changed out) won't spark until I plug in the light string onto the unit and complete the circuit, then it sparks out.
    So I believe there is something bad in the channel 1 circut on this board. So im looking at the components and it doesnt seem to complex, but im not really very savy in electronics.
    Apparently, for some reason, way too much current is getting to that little potentiometer. Please see the component I have circled. Can you help me identify what it is and do you think it could be the cause for the excessive current frying the potentiometer.
    Thanks
     

    Attached Files:

    Last edited: Jul 28, 2017
  20. hotrodjohn71

    hotrodjohn71

    28
    1
    Jul 22, 2017
    If you guys read all of that, I commend you :) Ive been closely inspecting this circut board and it looks like the main thing in the circut that could be bad is a silicone controlled rectifier. I have searched and searched and cannot find a cross reference. It is a Motorola item `SCR1590` and also a motorola stamp then `7913` which I think is a date code.

    Would anyone have the stats on this rectifier to cross ref it to another brand?
    Thanks
     
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

-