Hey guys i've got a JCM800 and im trying to get into the chasis to bias the amp but one of the screws that goes from the bottom is stuck and undo. it's essentially attached to the bolt on the otherside which has broken away from the chasiss so it's spinning in mid air.. i've just about managed to squeeze in a pair of plyers but i cannot get it to budge. Im so close to just smashing the head box to pieces to get into the amp and buying a new head box. im in absolute agony here my hands are killing me and i cannot get this thing open.. any ideas?
If you have a Dremel tool you might be able to grind away the exposed end and have that pull through the wooden cab. Then you can recover it once the head is out and epoxy the nut back to the chassis.
Don't smash up the head box or hurt your hands... Grind off the bolt head with an angle grinder, drill it out with a power drill, or cut it off by hand with a hacksaw or file if you haven't got power tools. You'll need to replace both the bolt and the captive nut anyway - don't try to epoxy the nut back in, it will just break again (sorry bosstone ).
That's cool John, I was just guessing anyway. I have never had to try it though there are some very strong epoxies out there like Marine Tex that is strong enough that it can be filed, drilled & tapped. I might hold if you did a good job of cleaning or roughing up the surfaces. It is worth a shot anyway because a spot weld would be impractical.
think john has the best idea.. i just dont have any tools. I'll ring my dad get him to bring over a saw or something.
I've had to do it more than a few times. The problem seems to be that the caged nut gets pushed up a little as the bolt goes in, at an angle so the bolt then cross-threads itself, and if you're using a power screwdriver you might not notice until it's too late. Then when you try to undo it the cage rips apart and you're left with no way of undoing the bolt because the nut just turns. Either that or the wrong thread bolt was used. It absolutely amazes me how a lot of people can't even keep track of four bolts when they take an amp apart. Over half the old Marshalls I work on have missing or mismatching bolts, it's really ridiculous.
yea well this is the first time i've opened it.. it's new to me.. but it's 21 year old amp so it's bound to have had some fool inside it.
