Analog receivers with short range.
 

They work, but the reception with a known good TX is very short range. Antennas were tested for continuity. Can they be adjusted or fixed some how?

Are you asking about old 27/75mhz equipment? If so, most issues with those would be traced back to bad crystals but they're not really going to be worth fixing beyond that.

Assuming good working order they probably can be tuned to the transmitter for the best range, that used to be a thing. But I agree with Mark, with affordable 2.4GHz systems that are inherently more stable it hardly seems worth it unless it's for a serious vintage project or for educational/curiosity etc reasons.

The guys are right, it's not worth the hassle unless you want to learn something by fiddling with them. Depending on how old they are, they might be designed for stagger-tuned IF, which is a lesson in itself.

But if you have the urge to tinker, hey they are already broken, so go for it. There's nothing to lose.

I know I still run 75mhz on some of my older cars when bashing, and there are days when there are "dead spots" in reception. It's usually less than 100 feet away from where I am standing. If I make it through that dead zone, the receiver works well. But passing through it, I lose most control. Other days, there are no problems.
So don't forget about good ol' rule 15 of the FCC regulations.