Jcm 800 2203 (no Sound) H.e.l.p.

Discussion in 'The Workbench' started by RyanScott, Oct 8, 2018.

  1. RyanScott

    RyanScott Member

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    All the tubes are lighting, the HT fuse is good, there is ZERO noise coming out of the amp, used different cabs and such. But I also noticed that although the tubes light, they are NOT SUPER HOT (before you couldn't touch them) without feeling some pain.

    What should I be lookin for?
     
  2. GIBSON67

    GIBSON67 Well-Known Member

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    Has anything changed from the last time it was working properly?
     
  3. tschrama

    tschrama Well-Known Member

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    No noise at all means no current through the output transformer. This is consistent with the tubes not getting really hot.

    So either the HT has failed: check the HT

    or the bias voltage has drop so low, that no current is flowing. : check bias current and grid voltage.
     
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  4. ampmadscientist

    ampmadscientist Well-Known Member

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    Blown fuse caused by incorrect speaker load or bad speaker connections.
     
  5. RyanScott

    RyanScott Member

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    I'm not thinking so because I had correct setting on the amp matching the cab.
     
  6. RyanScott

    RyanScott Member

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    Grid voltage test Im assuming on one of the Power Tube Pins?
     
  7. RyanScott

    RyanScott Member

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    Nothing has changed, shut her down and she never woke up.
     
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  8. tschrama

    tschrama Well-Known Member

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    If you have to ask about that, you should bring the amp go to a tech.
     
    Last edited: Oct 9, 2018
  9. ampmadscientist

    ampmadscientist Well-Known Member

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    That doesn't mean that there is nothing wrong with the speaker or speaker connections. (like a bad jack or a bad speaker cable)

    When the fuse blows it's usually speaker related. Remember this. :nono:
    If the fuse blows - it blows for a reason.

    Fuses don't blow by themselves - if the fuse blows, there IS something causing it to blow.

    1. Don't ever assume that there could be nothing wrong. If the fuse blows check everything. Especially the speaker cables and jacks.

    2. A bad connection inside a speaker plug can make the fuse blow.
    3. A corroded jack in the speaker cabinet can make the fuse blow.

    4. DID you measure the speaker with an ohm meter?
     
  10. RyanScott

    RyanScott Member

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    1. Speakers Cab and Cables work fine with my other JCM900

    2. No fuses are blowing (not sure where you read that)

    3. Speaker cab Ohm reading 15.7 (its a 16 ohm cabbie)
     
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  11. RyanScott

    RyanScott Member

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    Heres a thought? Bad Standby Switch??
     
  12. johan.b

    johan.b Well-Known Member

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    2203 or 2203x? ..If x, put a cable in the loop
    J
     
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  13. neikeel

    neikeel Well-Known Member

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    Let's see:
    Tubes lighting = mains fuse and heater circuit is working (probably ac HT out too, more later)
    Did you check the HT fuse with a meter (not just by eye?).
    Do the fx loop jumper first - quite common corrosion on the loop jack contacts.
    Also give the output selector a good wiggle as they can make poor contact sometimes.
    Next pull the amp from the chassis (usual rules of engagement re caps, although you should have bleeders on yours).
    Plug in with output tubes removed (no need for speaker load then) and with DVM check for dc volts between chassis and the probe for B+ voltage from the rectifier 470-490 is ballpark, clip to chassis, one hand in pocket other on probe.
    If that is good then measure plate voltage by moving probe to pin3 of each output tube, whilst there measure screen voltages (pin 4, smidge lower than plate) and for bias voltage on pin 5 (-ve volts of around 40 to 50v).
    After that post back.
     
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  14. neikeel

    neikeel Well-Known Member

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    Laggy net - double post!
     
  15. Rudy v

    Rudy v Member

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    Have you thought a bad phase inverter tube
     
  16. Ufoscorpion

    Ufoscorpion Well-Known Member

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    Are you sure you've not just suddenly gone deaf from playing a 2203 too loud in your bedroom ?
     
  17. myersbw

    myersbw Well-Known Member

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    I conquer with pulling the power tubes and voltage checks first (including each side of the Standby switch). Yank the speaker cable from the amp and measure the resistance with a meter.
     
  18. ampmadscientist

    ampmadscientist Well-Known Member

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    Take the power tubes out.
    Turn power on, turn standby to operate.
    Set DC voltmeter to highest range (usually 600 or 1000 volts)
    Measure pin 3 and pin 4 of each output tube socket. Red probe to pin(s), black probe to chassis ground.
    What is the readings?
     
    Last edited: Jan 1, 2019
  19. johan.b

    johan.b Well-Known Member

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    No posts since Oct.9...I think he solved it..
    J
     
  20. ampmadscientist

    ampmadscientist Well-Known Member

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    Well, he could have let us know...how gosh. :agreed:
     

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