Troubleshooting the Radio
Gary Tayman
|
Troubleshooting the Radio |
|
Gary Tayman |
|
Your Stovebolt is just a joy to drive. You've got heads turning and thumbs going up everywhere you drive. There's room for the whole family and the dogs. You've been hauling all kinds of neat stuff in the bed. Life is good ... but (in the old tradition of "it's never really finished") if only it had a decent radio ...
Well, here we go, Stovebolters! Here are some handy tips from Gary Tayman of Tayman Electrical
Sound Solutions For Classic Cars (what a fascinating site he has). It seems there's a lot of interest in sound systems but not much knowledge -- so we hope this will be a great help! And thanks to Kimberly McDowall, we also have this Tech Tip available in pdf format! ~~ Thanks Kim!
Trying to determine what is wrong and why the radio doesn't work? Well, it is not always the radio that is broken. And if it proves to be your radio after all, Gary has some very good suggestions on what to look for and where to go.
A non-working radio isn't always what it seems. The real culprit could be anything from a bad antenna cable to incorrect spark plug wires. The following are some troubleshooting tips to help you pinpoint the problem -- to either the radio itself or an external device.
#1. I know it's tempting, but ignore the dial lamp. On many cars, the lamp is on a different circuit from the radio. You can pull the fuse to the radio and the lamp will still light in many cases.
#2. With a voltmeter, or one of those cute light-up test probes, check the power lead to the radio. Don't forget to turn the key on to ACC! Check for 6 or 12 volts between the power lead and the metal dash (or car frame). If you don't know which lead is for power, it can't hurt to check every lead -- one of them should have 6 or 12 volts when the key is on.
#3. So you have power to the radio, but you still don't hear anything? Check the speaker. With an ohmmeter, or flashlight battery if you don't have all this tech stuff around the house, touch the probes or battery to the speaker leads. (On some cars there is only one lead; touch the other probe to the car frame.) Just like that bowl of breakfast cereal, you should hear some sort of faint snap, crackle, and pop from the speaker as you make contact. If you don't, the radio may be playing its heart out to a dead speaker.
By the way, in case you care, the ohmmeter should read about 3 to 10 ohms.
#1. Your speaker may pass the snap, crackle, pop test, but if the cone is warped or torn, it won't sound very good. Try another speaker.
#2. If reception is poor, try another antenna. Connect it to the radio and hold it out the window. Ignore the people who are looking at you funny; remember they don't have a classic vehicle like you do. Try out the radio -- you should get at least a handful of stations.
#3. Don't overlook the antenna trimmer. This is a small adjustment that is usually located near the antenna socket. On some radios it is found behind the tuning knob. To adjust, tune to a weak station between 1200 and 1400 AM. Adjust this (may require a screwdriver) for strongest reception.
#1. If the radio sounds fine
before you start the engine, the problem is under the hood. Make sure you have
resistor spark plug cables -- the reason for the resistance is radio reception.
Also, make sure you have the proper condensers on the generator/alternator
and/or voltage regulator.
#2. Here's where it gets fun -- your car's electrical system is old enough to retire. Connectors are corroded, switches are dirty, and these defects can manifest themselves in the form of radio interference. For example, let's say you're listening to your favorite doo-wop as you make a left turn. Flick the turn signal and the radio goes pop-pa-pop-pa-pop! There is a bad connection somewhere between the battery and the turn signal flasher, and the line voltage fluctuations are being picked up by the radio. You can verify this with your voltmeter -- assuming you have one. If you measure between the battery and the turn signal flasher, you should measure zero. But with a bad connection you may measure anywhere from half a volt to 4 or 5 volts! You can use that voltmeter to isolate the bad connection. Often the ignition switch itself is the culprit; don't overlook it.
#3. If you're doing all this in your garage, keep in mind that shop lights, air conditioners, and all sorts of other garage-type appliances can be a source of radio noise. Take your car down the street and see if the noise goes away -- or find a portable AM radio and see if it makes the same noises in the garage. If you do this, turn the car radio off. Otherwise both radios will squeal -- or did you know this? If you put two AM radios near each other, they will both make a squealing noise that will change in pitch if you tune either of them.
#4. On older tube type sets, a faint hum from the vibrator is normal. But if you hear a loud hum or buzz through the speaker, wrap it up and send it for service -- your filters have gone bad, a common problem with old sets which have sat around unused.
#1. When bench testing a radio, make sure the power supply is connected properly. Many people find the 6 or 12 volt wire, but connect the minus lead to another wire. Connect the minus lead to ground. For positive ground vehicles, connect the red lead to ground and the black lead to the power wire.
#2. Back in the olden days, vibrators failed left and right, and were user replaceable. Today you can buy a solid state replacement which is far better, but I don't recommend replacing it yourself. The reason is not because I'd rather you have me do it; it's because there are other components that, after 50 years, are usually bad and will blow even the best of vibrators. The worst offender is called a buffer -- it's a capacitor placed across the transformer secondary, designed to withstand voltage spikes of up to 1,600 volts. If the buffer is original, sight unseen I could bet you it's bad, and I'd win. If you're handy with a soldering iron, you have my permission to replace the buffer (make sure it's rated at least 1600 volts). While you're at it, replace every wax-paper capacitor in the set, and check the rectifier. Your radio will feel much better, and the vibrator should then be safe in its new home.
#3. Sometimes a user will buy all new tubes, with hopes of avoiding a repair bill. I'm going to save you a tube bill by saying that tubes almost never cause a radio to fail. One or two tubes may be weak, but this does not shut down the radio -- something else is wrong. Sometimes I get a radio that "worked poorly before, but after putting in all new tubes it doesn't play at all." Invariably the tubes are in the wrong sockets. No, they are not all the same. Also, never tighten the adjustment screws on the chassis, circuit board or IF cans. These are for alignment -- they don't tighten anything. Yes, people have done this . . .
#4. Finally, be careful where you send it for repair. Your local TV repair shop quit servicing your 50 year-old radio 45 years ago. They don't stock the parts or have the literature, and many have never worked on tube-type devices. On the other hand, there are nice folks, that I would like to include myself in, that specialize in vintage radio equipment, either as a hobby or as a business. We have the older literature, we have sources for many of the parts, we talk shop to each other, and we even buy test equipment -- much of my literature and test equipment came from another dealer in Clearwater. There really are resources for rare vintage parts, although sometimes it takes awhile to locate certain special items. But the good news is that there is a community of people who specialize in this older equipment, that can take care of you. If you've determined that your radio needs attention, please let me know -- I'm at your service.
Gary Tayman
Tayman Electrical
Sound Solutions For Classic Cars
Located in sunny Sarasota, Florida
If these tips don't cover it all for you ... or your hopelessly lost, Gary's got another Tech Tip for us on Shopping for a Used Radio. A big thanks to Gary for this Tech Tip and a big thanks to Stovebolter Richard "Richard2005" Rosielle for helping us get it together.~~ Editor
v. November 05
| No parts of this site, its contents, photos or graphics may be used without permission. |
|
|
