Faceplate Warping (Mojotone Plastic Fender Style) -Anyone Seen This?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by hardys, Apr 8, 2015.

  1. hardys

    hardys Member

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    I recently purchased a used, pristine 4 month old, Fender clone made by a highly respected boutique amp builder. I don't want bring any bad PR to him, so I'm reluctant to divulge his name.

    When the amp is cool, the control panel lays flat against the chassis. However, when the tubes heat up, the panel bows out away from the chassis. I looked closely on Mojotone's website and it appears this is one of their acrylic panels that can be custom engraved.

    The area circled in red below is where the bowing occurs. Has anyone seen this before? If so, what is the fix, if any? Thanks for any help in advance.

    [​IMG]

    BTW...I posted this in the "Amps and Cabs" forum as well for more exposure. Hope I'm not breaking any rules.
     
    Last edited: Apr 8, 2015
  2. RiftAmps

    RiftAmps Member

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    If it's bowing then the jewel light isn't tight enough against the chassis. They're a pain to get tight and it takes a full set of ninja fingers to do it properly. I suspect it's come loose and allowing the faceplate to move.

    Also......it must be ruddy hot inside the chassis if it's causing the plate to warp.....suggest getting it checked out
     
  3. Trout

    Trout Member

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    I have seen this before, actually experienced it before.

    The faceplate material expands at a greater rate than the chassis.
    When everything is tight including the pilot the trapped open space expands and follows the least resistance. Bulges upward away from the chassis.

    You " Might" get away with simply putting adhesive in the joint, clamp it down a day or so.

    I used GE Silicon II and it worked great.

    On a plastic reverse engraved faceplate you want to avoid an adhesive that dries hard or sandable. Eventually it will pull the paint right off the back.
     
  4. Chris Scott

    Chris Scott Silver Supporting Member

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    I'm with Trout - built a number of amps with Mojo faceplates, and because I'm such an anal perfectionist I glue them all down anyway, and so far no lifting.

    It's plastic, and as such I'd almost expect it to do that, so glue it down with an elastic adhesive.
     
  5. Bobby Smith

    Bobby Smith Member

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    You can try double stick tape too. I use it on my plex builds before I install any controls.
     
  6. J M Fahey

    J M Fahey Member

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    I see it on Matchless amps .... which are very hot mothers to begin with.

    There are 2 types of plastic panels, :

    * the sandwich type (usually black/white/black as in old Hiwatt) which needs engraving to show white, those you can glue or double sided tape with no problems.

    * the transparent reverse printed ones, such as Plexi or some Fender, where letters are silkscreened or engraved on the back, then the back is sprayed gold or black to provide a background.

    These are in danger of adhesives of any kind tearing or or its chemicals eating through the background paint ... result is horrible.

    How do I know?
    .......
    don't ask :(
     
  7. Trout

    Trout Member

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    What are the laser engraved ones classified as?

    They are clear with a color coat on the inside. Then a laser is used to remove the color coat leaving clear letters. Then a simple fill color is added after the laser process to make the letters opaque.

    BNP Laser makes a pretty nice one.
    They do however expand more than the metal chassis like others.
    http://www.bnplasers.com/index.html

    Pretty sure Amplates uses or used them at one time.
     
  8. gght

    gght Member

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    In theory you could slightly enlarge the pilot light hole. and leave the nut very slightly loose to relieve the pressure?
     
  9. Trout

    Trout Member

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    Actually, another similar approach.

    Open the hole for the pilot just enough for the pilot flange to seat on the chassis and not the faceplate.

    I have an amp like that and it does work well. It has less than a 1/32 difference in diameter, just enough for the expansion.
     
  10. donnyjaguar

    donnyjaguar Member

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    Play the amp until the faceplate pops up, loosen the pilot light fixture, smooth down face place, re-tighten pilot light. :)
     
  11. Chris Scott

    Chris Scott Silver Supporting Member

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    Nice thought, but that nut needs to be tight, as it's also the filament connection off the pt, and it can render real problems if it moves, possibly allowing the fils to short to ground.:nono
     
  12. Chris Scott

    Chris Scott Silver Supporting Member

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    There you go, somebody's using the ol' noggin...
     
  13. Chris Scott

    Chris Scott Silver Supporting Member

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    Good point, and I would have to agree that depending on what product you use, the results could really ruin one's day, as some chemicals just don't like some other chemicals.

    Fwiw, I used 30 minute epoxy on the 3 different plexi - style projects, all of which used the Mojotone panels and they have all been flogged mercilessly with no issues thus far.

    Again, take it for what it's worth...:dunno
     
  14. hardys

    hardys Member

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    My panel is black & white layered, with the amp's name etched into front, which produces a white name on the black background. So, there's no worries about affecting the looks by putting adhesive or double faced tape on the back.
     
  15. swiveltung

    swiveltung Member

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    I thought Mojo's were steel?
     
  16. hardys

    hardys Member

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    The stock "no logo" ones are steel, but the engravable ones (which mine is) are acrylic.
     
  17. walterw

    walterw Gold Supporting Member

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    haven't messed with this, but i imagine you could take a rattail file and widen the inboard sides of the two holes flanking that open area; you should be able to have the knob and the jewel cover up the holes still, while creating enough room for the expansion to not push the plastic against those two mountings, causing the bulge.
     
  18. hardys

    hardys Member

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    Even though I just bought it used, under it's transferrable warranty, the builder has agreed to fix the faceplate.

    Thanks for all of the great suggestions on how to fix the problem fellow forumites!
     

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