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Mesa M9 Carbine Head

Discussion in 'Amps and Cabs [BG]' started by ca7922303, Dec 15, 2018.


  1. ca7922303

    ca7922303

    Jun 17, 2014
    This head has a low distorted output signal. I replaced the 10 MOSFETS w/ Exicon MOSFETS from Profusion of England. Have same low distorted output as before. I am working on this amp due to finances and would appreciate any ideas I can get. Thanks.
     
  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Did you test the MOSFETS first?

    I'm going to offer a bit of advice here... it's absolutely critical to actually troubleshoot the amp BEFORE replacing parts. It's likely that all 10 original MOSFETS are perfectly fine. Since it's an open loop source follower circuit, the obvious first troubleshooting step is to look at the signal at key points throughout the circuit (including the gate drive to the MOSFETS) and measure key DC operating voltages to see where you do not get the expected results. This is the ONLY reliable way to repair any amp. You do have a signal generator, scope and meter right? Do understand how these circuits are supposed work and the voltages that the different circuits operate at?

    You wished to save money, my suggestion would have been to find a factory authorized service center or even the factory service program which would have avoided the (substantial) cost of replacing perfectly good parts. Your amp would have also received any necessary updates and a full tune-up. Did you at least buy the correct Exicon parts?
     
  3. ca7922303

    ca7922303

    Jun 17, 2014
    Alfet 16p20w & 16n20w MOSFETs were replaced with exicon 20p20w & 20n20w new MOSFETs.
     
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I'm assuming you mean ECW20p/n20?

    Without getting into documentation, these parts are not directly compatible and using the Exicon requires additional gate drive overvoltage protection when substituted for the Alfet part. I do not know if the M9 has this or not as we didn't use Exicon for production. These are the kinds of things that have to be considered whenever changing parts, it's possible to create a problem that you didn't have originally.

    You will need to troubleshoot the amp step by step to identify where things are not right.
     
  5. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    Yikes.
     
    agedhorse likes this.
  6. ca7922303

    ca7922303

    Jun 17, 2014
    Yes ecw20p &20n were installed. Rich @ Mesa gave me the exicon of England reference. He agreed that it sounded like a MOSFET issue. Trying to move forward. Do you have any ideas on next likely step. Thanks for your help.
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Yes, troubleshoot properly.
     
  8. ca7922303

    ca7922303

    Jun 17, 2014
    Im unable to get a schematic for the M9. Im getting ready to buy a M6, partially due to the fact that I'm thinking the circuits are the same except for the eq and compression. Can you tell me if they are in fact the same? Thanks for your help.
     
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    They are similar but not identical.
     
  10. ca7922303

    ca7922303

    Jun 17, 2014
    Is the MOSFET block interchangeable?
     
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    No, not directly.
     
  12. ca7922303

    ca7922303

    Jun 17, 2014
    The board in my m9 is labeled impulse 600 so I assumed its the same board for mpulse 600, m6, m9?
     
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Just because the physical PCB is the same doesn't mean that the circuitry is the same. There are similarities but there are also differences. I'm not going to get into the details because there were different versions of all of those products and all I would be doing is provide misleading and inaccurate information.

    Assumptions are usually incorrect when you know more about a product.
     

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