I have the mirror image of yours, a DX-300 that only displays Khz. but not Mhz.
It came with a bunch of estate sale stuff I bought last year and I haven't had a chance to go inside it yet.
Given the abundance of Radio Shack stores, the DX-300 and DX-302 were probably the biggest sellers of the Wadley loop design receivers although the Yaesu FRG-7 was also very popular. The performance of these realistic receivers isn't on par with the original Wadley classic (Racal RA-17) but it works decently and was a lot cheaper and lighter. The greatest shortcoming is that it overloads easily.
Hopefully the problem will be easily solved.