1998 JCM2000 DSL 50, not working right. Barely any gain, weak sound

Discussion in 'The Workbench' started by Clockworkmike, Jan 24, 2020.

  1. Clockworkmike

    Clockworkmike Member

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    Hey guys, been gone from here for a long time ( had kids, changed jobs, got busy with life's hurdles lol) but I gotta weird problem with my amp. I had asked this question a few years ago, but never got to fixing it.

    What's happening is I have a 1998 JCM2000 DSL 50 head that I got when it first came out. Loved the amp and used it relentlessly during my younger years when I actually had a band, had the time to play etc. Fast foreword many years and barely getting to play like I used to, I decided to start toying around with this amp again but it went on the fritz. I changed my tubes all out ( using 2 JJ El34B and 4 Shuguang Silver Dragon 12AX7Bs) they seem to be glowing fine but the amp is pathetic sounding now.

    When using the classic channel without crunch, i have to dial it up to around 4-5 just to get a sound out of it. Hitting crunch, it's about 3-4. Neither has any gain hardly at all, yet the preamp controls all seem to work, as does reverb.

    Meanwhile, over on the Ultra Channel 1 it's got some mild gain at around 3, click it over to 2, it's about the same volume with just a touch more gain.

    I noticed if using a processor/preamp plugged directly into the FX loop return ( bypassing it to a Poweramp) it's volume is fine. But trying to use the FX loop thru send and return, plugging into the front kf the amp, nothing really.

    This has got me fairly stumped to be honest. I checked the bias output and metering between the center pin and left side, it's at 42mV ( that's the pot all the way down) and on the right it's 43mv ( pot all the way down as well). I even tried replacing each preamp tube with an existing Svetlana 12Ax7 I had, one socket at a time, nothing.

    I figured I'd come here and see if I could find some great advice and try to fix it myself. But worse for worse, I guess I would have to send it off to the nearest certified repair center : Sundown Productions in Ashland, Ky ( anyone ever had any experience with them btw? Marshall recommended them)

    Thanks in advance!
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    It's a preamp problem that requires test equipment. You already did everything you can do.
     
    Clockworkmike likes this.
  3. Clockworkmike

    Clockworkmike Member

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    I kinda had this feeling to be honest. Ugh...well, at least it's tax season and I see where my refund is headed lol. I appreciate your time though!
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    There should be IRS form 1959, which credits Marshall players for maintenance.
    There should be output tube deductions.
     
  5. Clockworkmike

    Clockworkmike Member

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    Hahaha absolutely!
     
  6. Clockworkmike

    Clockworkmike Member

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    It's alive!! I took the JCM2000 DSL50 to an amazing repair tech a couple hours away ( shout out to Guitar CPR!) and after about 2hrs , he figured out the problem: the input Jack had basically came off the board minus maybe 2 pins, thus the awful weak sound.

    But there was some other issues: I bought this amp brand new from a shop that was closing and have never had it serviced before this. Apparently, someone had been in the amp before I got it and had attempted some small repairs. Something had happened where they tried , very poorly, to resolder some points and circuit traces and had a lot of solder splatter across the board and tried to hide it using green dielectric paint. Obviously this wasn't a factory job because it was on top of the board. He cleaned it up with acetone and properly reconnected the bad traces and voila! Back in business

    Now in case you're wondering how was someone in it if I bought it new? Easy: the store I bought it from closed about a month later after I bought it and had a very nice reputation of salesmen taking out equipment from the shop, using it for gigs, then bringing it back the next day ( my uncle actually worked for them and confirmed this practice). My theory ( and I can't prove it definitely) is that they used this amp, damaged it and tried to repair it without anyone noticing it. So much for buying "new".

    But hey, it's fixed!
     
    marshalltsl likes this.

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