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Thread: Johnson Amplification JM150 LCD display repair...

  1. #1
    Senior Member pecorporation's Avatar
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    Johnson Amplification JM150 LCD display repair...

    This question may be moot, but I have to at least ask. Is there any replacement parts or repair fixes for the LCD display on a Johnson JM150. Everything works and the amp responds and passes a signal and the back light illuminates the LCD display but the screen is blank, displays no characters.

    Everything I've read online seems to indicated the customer is S.O.L. so I thought I'd check with the experts!

    Thanks in advance,

    Steve
    CAUTION!!! Solid state and tube amplifiers contain lethal voltages and can retain them even after unplugged. Refer service to qualified technician.

  2. #2
    Supporting Member Jazz P Bass's Avatar
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    Yeah, SOL for sure.
    That display has a character driver chip that is specific to that particular LCD.
    Attached Thumbnails Attached Thumbnails johnson_jm150_featured.jpg  

  3. #3
    don't forget the joker g-one's Avatar
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    Have you tried a re-boot? Otherwise the only generic repairs for displays I can suggest are that some may have elastomer strips that could be cleaned or maybe low power regulators (78L05?) which could go bad. Beyond that, what JazzP said...
    "Thank you. Now on this next one , ladies and gentlemen, I'd like you to pay attention to my tone - not so much my singing or the band... " - JP Lepage

  4. #4
    Senior Member Enzo's Avatar
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    A visit to their web site shows 801-566-8800 as the phone, and you can order parts.


    Just for grins, have you tried reinitializing the thing? A bad bit in memory could be sending blanks to the screen.
    Education is what you're left with after you have forgotten what you have learned.

  5. #5
    Senior Member
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    Needless to say, that you can perform the hard reset:

    1. Press and hold the CONFIG button while powering the amp.
    2. Release CONFIG button after about 5 sec (in fact you
    must see an asterisk appearing in the information line on the screen,
    but in your case LCD shows no information).
    3. Press MOD button.

    If this does not help, see below.

    If encoders affect the sound, the digital core is OK.
    Check control signals on the H15 connector. You must see “low” level on the pin 11 and pulses (at least when you turn encoders) on the pins 10 and 12. If all control signals present and LCD shows no information, you need to order new LCD (its p/n 30-6297-A).
    If at least one of the control signals is wrong, check what’s the matter.

    By the way, do you have the JM-150 schematics? If you need, I can upload it here.

    Good luck

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