VU meter not working

Discussion in 'DIY' started by hrpuffnstuff, Nov 30, 2012.

  1. hrpuffnstuff

    hrpuffnstuff AK Subscriber Subscriber

    Messages:
    121
    Location:
    South GA
    Well, I have my Hitachi HMA-8500 MKII amp apart trying to fix the right VU meter. The left meter works fine, so I disconnected the molex connector at the circuit board where the two VU meters get powered. I next unsoldered the wires going to the right VU meter and jumped directly from the pins on the circuit board to the right VU meter--still no dice. Just to make sure my test worked, I also jumped to the left meter and the left meter works as expected. Apparently there is a problem with the meter. Can these things be repaired, replaced, or ??? Before I put it back together, I thought I would check with you all. I don't know if it will help, but schematic attached.

    HF
     

    Attached Files:

    Last edited: Dec 2, 2012
  2. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,538
    Location:
    uk.. the middle bit
    if the bearing is tight for the needle it can be cleaned and lubricated ..if the coil is burnt out i don't know ..never been there .. be careful with spring its damn delicate .
    just thought of another test ..dmm on diode test probes on meter contacts then reverse test leads . meter should move pretty quick so quick test only .
     
    Last edited: Nov 30, 2012
  3. Trio

    Trio Super Member

    Messages:
    2,211
    i have dismantled more than a few, for various reasons too- rewiring them is not easy and I would not even suggest trying it- your time and sanity are worth more than a used VU meter.

    It is possible that a lead may have fatigue failed. That could be repaired and I have done it out of need. The problem is those VU meters are not made to be repaired or even opened up beyond prying loose the plastic face.
    What makes the meter work is the applied current flows part of the movement- both of the pivots are the contacts, the circuit completes through the windings.

    If it were me, I would just look at buying a used VU meter. If you never opened one up to repair it, place a value of about 2 to 4 hours of your time on it. i spent about a half hour on a real cool brass voltmeter about 3 inches across and bailed a half hour into it because I saw what I was in for.
     
  4. hrpuffnstuff

    hrpuffnstuff AK Subscriber Subscriber

    Messages:
    121
    Location:
    South GA
    I also recently noticed that I dont get sound out of the right side when I plug headphones into the headphone jack. I looked at the schematic. Am I correct when I see that the right meter and right headphone audio are connected by R791R, R792R, and R793R resistors. Could a bad resistor be causing both problems?
     
  5. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,538
    Location:
    uk.. the middle bit
    looks like the meters connect to the relay and not through them resistors .
    the schematic is all a blur so cant see what is before the relay ..are they fuses ? plus that switch might need cleaning
     
  6. hrpuffnstuff

    hrpuffnstuff AK Subscriber Subscriber

    Messages:
    121
    Location:
    South GA
    Last edited: Dec 5, 2012
  7. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,538
    Location:
    uk.. the middle bit
    still a blur but look like fuse resistors before the relay ..check one against the other .. power off meter on ohms ..
     
  8. hrpuffnstuff

    hrpuffnstuff AK Subscriber Subscriber

    Messages:
    121
    Location:
    South GA
    Yes, there are fuse resistors before the relay. How do I "check one against the other...power off meter on ohms"? I don't understand what that means?
     
  9. petehall347

    petehall347 the brandy coffee man

    Messages:
    23,538
    Location:
    uk.. the middle bit
    just check with your multimeter ..measure the ohms .. amp unplugged ..
     
  10. refrigman

    refrigman New Member

    Messages:
    8
    I am parting out HMA 8500ii if you need any parts i can probably help
     
  11. Jon_Logan

    Jon_Logan Addicted Member

    Messages:
    6,881
    Location:
    Left Coast
    Stuck meter issues are very common.

    I have dismantled a few meters and replaced the guts, attached the coil wires to the contacts, adjusted the pivots etc.

    I am here to tell you:
    If you can free it up without taking it apart, that is the best way to approach it.

    Using a DMM's diode test to force current onto the coil and exercising the meter is best, if it can be done. The pivots won't tighten themselves on their own. Usually, the lubrication thickens. If the pivots are too loose, you'll lose a reliable contact. Most meters use one of the pivots as a conductor.

    Try the diode test function and see if repeated pulsing will allow the pivots to break free. The diode test is limited to about 1mA on most meters and that is safe to drive the meter coil.
     
  12. hrpuffnstuff

    hrpuffnstuff AK Subscriber Subscriber

    Messages:
    121
    Location:
    South GA
    I sent you a PM refrigman...i do need some parts. Thanks for the info.
     

Share This Page