Hi guys. Yup, start with the fuses. All electronically-tuned radios have two fuses; one that turns the power on with the ignition switch, and one for the station preset / clock memory circuit. That memory circuit is almost never labeled for the radio like the first on is. The memory circuit is always tied in with some other circuit that is always live. The most common is the interior lights, but it could also be the horn, cigarette lighter, or even the brake lights.
The clinker is every radio model acts differently when the memory circuit is dead. Some radios will be totally dead. On some, everything mechanical and the display works, but there will be no sound. A few GM and Chrysler models will work perfectly fine except each time you turn on the ignition switch, the station will go back to a factory default setting, and the clock will go to 12:00 on Chryslers and 10:00 on GMs.
GM used to have a lot of trouble with "griplets" on their circuit boards. Those are sort of like rivets that connect a copper trace on one side of the board to another trace on the other side. Resoldering them never seemed to be the permanent fix. We had to run wires all over to solve a whole list of intermittent problems. That is the clue to a bad connection. It is intermittent and will work at times. Most of the time when a part fails, it is permanent and doesn't work once in a while. By the early '80s they were using little pieces of wire through the griplets so those don't cause a problem any more, but intermittent solder connections is still pretty common. I press on the circuit board to verify I haven't found the culprit yet, much to my frustration, then I go looking again. Bad connections in tvs are usually real easy to spot. Not so in these radios for some reason.
Also, most GM trucks of this era had three-piece systems. There was the head unit, the body, which was behind the dash, then the separate cassette mechanism. 99 percent of the problems were caused by the box in the dash, but the last I heard, a few years ago, having one rebuilt only cost 40 bucks. If that is what you sent in, you might have gotten your old one back, but more commonly they just send one out that was rebuilt earlier. There could be a problem in that box that didn't show up at the repair shop, so they weren't aware of it. Also, you have to watch the part numbers on those because there's AM, AM stereo, and I think a couple of other versions. They all interchange / plug in but you'd like to have the same features with the replacement.
GM locked up all their radio repair business so I can't help if parts are needed. '94 is the last year they allowed me to buy service manuals for, and now their two authorized repair shops won't sell us parts either. I have hundreds of parts radios, but I need a model number and part number, then I can't guarantee my used part is good. The other problem with GM is there can be dozens of different radio model numbers for one model year that all look exactly the same and are almost identical inside. They change just a few parts to adjust the tone response for the car / truck body shape, so I could have a pile of radios that are the same as yours but I wouldn't know it because of the different model numbers. Chrysler adjusted their tone response mostly with different speakers or the use of a remote amplifier. They only had a few radio model numbers for many years. When you go to a salvage yard looking for a radio, you're better off just looking at the face plate and the plugs on the rear. Don't worry if the model number is different.
What I would do, if fuses aren't the problem, is first, pull out the box from behind the dash, and you'll see two plugs that each have four wires. If you have the radio that is all self-contained in one unit, pull that out and look for the same plugs. '89 was right in the middle of when they were switching from three large rectangular plugs to four smaller ones. The forth one usually isn't used. If you have the large plugs, look at the black one. If you have the smaller plugs, either on the radio or that separate box, I think it was also the black one. One of the four wires in that plug must have 12 volts all the time. That's the memory circuit. A second wire must have 12 volts only when the ignition switch is turned on.
If both of those voltages are there, stop in at a salvage yard and ask if you can borrow a box to try. For no sound, any box will do. The head unit doesn't have anything directly to do with sound. All it does is control the receiver box. The head unit could have a problem with the volume control, but that would not be common. If the receiver box solves the problem, they should be willing to sell it to you quite inexpensively. While they did have a fairly high failure rate, I'm sure they took in a lot more trucks over the years than boxes they could sell. They probably threw hundreds of them away, and they're losing the number of prospective customers who may need one. You should be able to negotiate a good price, at least less than the forty bucks it cost to have one repaired.
Tuesday, May 24th, 2016 AT 10:00 PM