Tom, I think Kato has made several different runs of the F7. It this is the one I think it is because of it being on the secondary market, it probably has a split frame with the two halves insulated from each other. Is that correct?
If so, my split-frame Kato units have the light board or drop-in decoder held in place by a gray clip. It's slightly oblong, about 1/8 in by a little longer, with two tiny holes in it. On the bottom are two prongs that snap into the frame through a hole in the PCB. You can pry it up from the sides by slipping a razor knife under and gently twisting it. The PCB should slip right off after the clip is removed. Make sure you get the contacts in the right places when you put it back on.
For your problem, you might not need to remove the PCB. Carefully look over the contacts coming up from the trucks. Look at the long strips that they touch, which carry the current to the motor contacts. See if you can tell how the jammed one differs from the others. You may be able to fix it without any further disassembly. You can remove the truck if you must. If you just slightly loosen the screws holding the two frame halves together, you may be able to twist the trucks out of the frame and solve the problem with the contact being wedged. Straighten the contact if it's bent. If it seems longer than the other one on this truck and the ones on the other truck, it probably isn't seated properly on the gear tower and in the side frames. That would cause it to jam.
Make sure the long brass strips that connect the tops of these truck contacts and the motor contacts are bent the same, and the one on the jammed side is positioned the same as the one on the other side.
If all that doesn't fix your problem, come back and tell us. We can guide you to disassemble the truck and check the position of the brass or phosphor bronze contact (not sure which metal it's made of, they look a lot alike and I haven't looked at mine in a while.) The trucks aren't hard to take apart, and they are simple to reassemble. It may be tricky to figure out how to hold all the pieces while you snap the side frames back on, is all.
One last thing, if you disassemble the trucks make sure the side frame/bottom piece is snapped all-the-way into place. If not, it may run but will probably drag causing wear marks on the bottom and probably derailments, especially at turnouts and diamond crossings.
Hope this helps.
Bill B
