Tweet
Some time ago, being fed up with finding the nylon snap-lock standoffs broken on the Vox AC30-6/TB PCB, with only a couple left that hadn't yet broken off, I finally measured the height of those snap-lock standoffs, finding close to 3/4", and ordered some # 4-40 nylon standoffs (not spacers) and some nylon # 4-40 PH screws. Slotted was all that's available, as far as I know. The two bags of parts sat on my shelf, not having any AC30's in at the time, and finally another AC30-6/TB came in with all but two of the snap-locks broken. While having the board out on doing maintenance to it, I finally dug out the Nylon Standoffs and screws, and removed the original snap-lock parts.
First issue was the hole size in both the chassis and the PCB. Substantially larger ID than what was needed, so hole registration would be a problem. I fetched some nylon # 4 shoulder washers from my TO-220 hardware drawer, and that was enough to center the # 4-40 screws. I first tried the nylon screws, but, as those tend to strip with the greatest of ease (not enough thread on the ones I had), I changed to # 4-40 x 3/8" PHMS steel Philips, and installed them, using a # 4 ITL washer underneath the standoff on the inside of the chassis. After I got all the hardware changed out, setting the PCB back into the chassis, I was greeted with the second problem. The PCB holes did NOT register with the chassis mtg holes. The chassis holes were a good 1/16" lower than the PCB thru-holes. (Probably responsible for the breakage of the snap-lock?). Would adding ITL washers and fiber washers onto the pot mtg bushings and the Cliff Plastic jack bushings re-align the holes? Was there enough bushing thread to do it? Yes. That was just enough to bring the holes into alignment.
That sure made it easier to get the PCB in and out, no longer having to fight the snap-lock end of the standoffs and get all of them to register with the PCB holes, and continue having them break off. And, of course, rotate on you while you're trying to release the silly lock on each.
First issue was the hole size in both the chassis and the PCB. Substantially larger ID than what was needed, so hole registration would be a problem. I fetched some nylon # 4 shoulder washers from my TO-220 hardware drawer, and that was enough to center the # 4-40 screws. I first tried the nylon screws, but, as those tend to strip with the greatest of ease (not enough thread on the ones I had), I changed to # 4-40 x 3/8" PHMS steel Philips, and installed them, using a # 4 ITL washer underneath the standoff on the inside of the chassis. After I got all the hardware changed out, setting the PCB back into the chassis, I was greeted with the second problem. The PCB holes did NOT register with the chassis mtg holes. The chassis holes were a good 1/16" lower than the PCB thru-holes. (Probably responsible for the breakage of the snap-lock?). Would adding ITL washers and fiber washers onto the pot mtg bushings and the Cliff Plastic jack bushings re-align the holes? Was there enough bushing thread to do it? Yes. That was just enough to bring the holes into alignment.
That sure made it easier to get the PCB in and out, no longer having to fight the snap-lock end of the standoffs and get all of them to register with the PCB holes, and continue having them break off. And, of course, rotate on you while you're trying to release the silly lock on each.