what we are trying to determine is if any signals are actually making it in to the radio and just not strong enough to be detected, or if there is something blocking them from being received in the first place.
first, use this schematic:
http://www.cbtricks.com/radios/uniden/washington_mb8719/graphics/uniden_washington_mb8719_sch.pdf
if the receive turns out to just be very weak, the radio might have been messed with and someone messed up the receive tuning coils.
dont start turning them just yet. chances are, if this is the case, that they are so out of tune that you could mess them up further before you know it.
if there is no signal being received at all, then the first thing to check is IC5 pin 6. there should be about 8 volts on it in receive.
is there?
if there is, next thing to check is TR9 the first RF amplifier.
you need to learn how to check transistors and diodes using your DMM, and you have to remove the part from the PC board to test it.
here is a link to help you learn how to do this:
Testing semiconductors with analog and digital multimeters
if this stuff seems over your head, then its time to seek out a tech to fix it for you.
other parts to check when getting started are: D13 and D14, D21 and D22, TR13, TR10, TR17, and TR16.
yes, this is a shotgun approach, but without you having test equipment such as a signal generator and a frequency counter (not the kind that connects to the antenna jack), i cant tell you how to check for certain freqs to be present or inject a signal at a certain point to see if operation is restored.
there is also the possibility that an electrolytic capacitor has gone bad/dryed out.
easiest way to check for that is to bridge a good one of the same value across the suspected bad one, but you are going to have to do that on your own.
look around the transistors i mentioned using the schematic, find the associated electrolytic capacitors, and start with those.
sorry to be so general, but as you can see, this is something that could be very easy, or a real head scratcher.
good luck with it,
LC