I didn't expect that they would. I don't know what the + would do (perhaps it was a never-realized function to enable tuning to either side of a frequency). The tailing "8" would be used in models that tune in 50kHz steps on the FM band.
Yes, I'm a display nut. I like looking at the characters inside them.
LEDs dim as they age, so that's not unusual to hear. It usually takes them a long, long time to go completely dark, if they ever do. However, a lot depends upon how much current they are driven with. LEDs driven "hard" (to make them brighter) will have shorter lifetimes.
That not all of the signal strength LEDs would often be illuminated at once makes complete failure a very unlikely situation. While each LED will have a quoted lifetime estimate, there are also variations in the lifetime of each LED. I think you will find a problem in the LED driving circuitry or its power supply.
Properly made ones typically won't. The most common sign of bad solder joints is a circuit that starts working when whacked, prodded, flexed or shifted, causing the bad joints to suddenly make contact.
Your receiver's power supply will have numerous outputs...high voltage/current outputs for the amplifier and lower voltage outputs to run the logic, indicator lights and "other stuff". I would expect the tuner to not actually work if a power supply voltage were missing/insufficient, but I don't know how JVC designed the circuit.
Here's how I'd go about it.
There are some good repair threads here on AK, including
this one. Note that you do
not to break the bank on all manner of test equipment. Many things can be fixed with a multimeter and some logical thinking. You may also want to visit the
sci.electronics.repair FAQ web site for some ideas on getting started with electronics repair.
1. Get a service manual for your receiver. Someone here may have one, or you could buy one. I've used StereoManuals.com for reproduction (or in some cases, original) manuals in the past. I have no affiliation with them other than as a satisifed customer.
Having the service manual is a good start, especially if you don't have a lot of experience tracing circuits and figuring out what is what. You'll see how electricity is directed through the circuitry. With a little studying to know what the various parts do, you'll have a better understanding of how JVC designed your receiver and what it should be doing when working correctly.
2. If you don't have a decent multimeter, you might want to pick one up. There are many good choices on the market. It doesn't have to be expensive, just reasonably accurate and equipped with certain testing ranges.
3. Making the actual tests will involve setting up the receiver so you can get at the LED board. You would then take DC voltage readings from the pins of each LED on the board while the receiver is powered and set to a function where the LEDs should be on (in this case, with a station tuned in).
How you will want to do this will vary depending upon how the receiver is built and your workspace. The most important thing is your safety. The receiver should be arranged such that it can't fall, and you should take the most care not to touch anything that might be directly connected to the AC power line, such as the terminals where the power cord connects, the power switch, fuse/fuse holder, etc.).
If you don't feel comfortable doing this, you certainly do not have to do so. Practicing first on another less valuable or important set would also be a good idea. That way, if something goes wrong, you won't feel quite so bad about it.
