properly taking measurements with a voltmeter

Discussion in 'The Projects Forum' started by Sho Bud, Mar 21, 2013.

  1. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    I've measured a few points on this circuit, but i'm getting readings that don't match what the schematic says i should be getting. What should my voltage readings be for the Red, Green, and Yellow wires coming off the transformer?

    Thanks for any help with this.


    [​IMG]
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Where are you connecting the other test probe?
     
  3. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    A ground on the power supply. I think it was the "E" right next to point "54" on the schematic.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,016
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    What voltage should they be and what do you measure? I don't see them listed on the schematic.
     
  5. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    I'm not sure what the voltage should be. I thought maybe there was something i was overlooking in the schematic. There's no label on the transformer or anything.

    I just found the service manual for this thing, and noticed a bit of info. The bottom left of the diagram has a picture of the power supply with voltages all within the range of what i'm measuring off of the transformer. Please let me know if I am correct.

    [​IMG]
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    First you said the voltages were off and now you say they are correct? I don't understand. :confused:
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
    970
    There "seem" to be a few voltages shown on the schematic but some also have a waveform associated with them so you really need an oscilloscope to see that. A typical meter will not show that information.

    But yes..I agree with crutschow.. quite a confusing post.. I can't tell if something is actually broken and you are trying to fix it or if you are just playing around.
     
  8. Sho Bud

    Thread Starter New Member

    May 28, 2010
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    Sorry. I'll try and explain a little better.

    There are points on the schematic that are labeled with specific voltages (point 54 on the power supply circuit for instance is labeled 45v). I've measured point 54 and i'm not getting anything close to 45v.

    I thought maybe there was something wrong with the transformer, so i started measuring that. I had no idea what voltage the transformer should put out until i found that last diagram that looks like it has voltages referring to the transformer. My voltage readings for the transformer almost match what the diagram has listed, so i'm assuming it's correct.

    I see what you mean about the waveform symbols on the schematic, and that makes sense. I didn't know what it meant.

    This project started when i couldn't get the reverb to work. That's when I started measuring everything else. That's essentially what i'm trying to fix.

    Everything else seems to be working, but why do you suppose i'm not reading 45v for point 54?

    I hope that made my question a little clearer.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    The point (54) is feeding the ERASE heads of the recording mechanism and will be a high frequency AC signal that may be riding on top of a DC level.

    You say everything seems to be working. Don't argue with success and, "if it ain't broke, don't try to fix it."
     
  10. Sho Bud

    Thread Starter New Member

    May 28, 2010
    11
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    @ BillB3857

    Everything works except the reverb function.

    How do i measure point 54? I'm only getting 1.6v AC, and .06v DC.
     
  11. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    I think for any more troubleshooting you will need a scope. The block diagram seems to be pretty straight forward as to how the unit should work.

    Is the tape motor running? Is the tape moving past the heads properly? It may be a mechanical problem.
     
  12. Sho Bud

    Thread Starter New Member

    May 28, 2010
    11
    0
    I hear ya. Thanks for your help!
     
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