Common faults
Repairing Radios
Though in-depth repair of car radios requires a fair bit of specialist knowledge and often some equipment there is a certain amount that can be done by the owner using only hand tools. First though, a warning. Though car radios operate from a twelve (or six) volt supply, up to 300 volts is needed across the valves and a vibrator or transformer is provided to step up the voltage. Thus a connected up and switched on valve radio can give a nasty shock to the unwary 'prodder'. So be careful! Many of the radios that I am given to restore are in pretty awful condition. The most important thing is that all the detachable knobs and switches are present; a set's internals can be repaired but, if a knob is missing, the chances are it will be almost impossible to find an exact replacement although in some cases replacements can be made.
Fault finding can be a time-consuming, painstaking business. I find that the worst faults to track down are man-made, i.e. where someone else has already had a go and attempted to make the set work. First stage is obviously to get the thing working, then bring its performance up to scratch by replacing 'soft' valves, condensers that are breaking down etc. Tracking all these faults down and circuit tracing is outside the scope of DIY as it involves special equipment. There is, however, a certain amount of simple fault tracing and rectifying that the ordinary person can do.
Parts Availability
Most components for valve car radios can still be found without too many problems; I can supply valves, vibrators etc. in cases of difficulty. The problem, as already stated, is with the trim parts such as knobs and switch buttons etc. When looking for period radios in autojumbles and sales try to find one that is complete. Don't be too concerned if the radio looks tatty; if all the original parts are present this can be rectified.
Though in-depth repair of car radios requires a fair bit of specialist knowledge and often some equipment there is a certain amount that can be done by the owner using only hand tools. First though, a warning. Though car radios operate from a twelve (or six) volt supply, up to 300 volts is needed across the valves and a vibrator or transformer is provided to step up the voltage. Thus a connected up and switched on valve radio can give a nasty shock to the unwary 'prodder'. So be careful! Many of the radios that I am given to restore are in pretty awful condition. The most important thing is that all the detachable knobs and switches are present; a set's internals can be repaired but, if a knob is missing, the chances are it will be almost impossible to find an exact replacement although in some cases replacements can be made.
Fault finding can be a time-consuming, painstaking business. I find that the worst faults to track down are man-made, i.e. where someone else has already had a go and attempted to make the set work. First stage is obviously to get the thing working, then bring its performance up to scratch by replacing 'soft' valves, condensers that are breaking down etc. Tracking all these faults down and circuit tracing is outside the scope of DIY as it involves special equipment. There is, however, a certain amount of simple fault tracing and rectifying that the ordinary person can do.
| Fault 1. Radio completely dead. i.e. no dial light, no sound when tutned on. | Rectification a. Check that fuse is OK; being the weakest link in a chain they sometimes 'blow' without any apparent reason, but check also that there isn't another fault that has caused the fuse to go. b. If the set is installed, check that the earth connection is good. Also, if the set has been installed by an amateur, check that there is a proper earth; a set will sometimes work earthing through the aerial, but reception will be affected, and aerial movement may make the earth connection intermittant, leading to intermittant operation. Check this if your set appears not to work when the car is at high speeds, or driving through cross-winds! c. Check for loose leads, loose connections, plugs in back of set loose, etc., etc. |
| Fault 2. Radio dead, no sound, but dial light comes on. | Rectification a. Check speaker is OK by substitution, also ensure speaker leads are tight. b. If radio has a separate amplifier unit, make sure that connections from this to the receiver are sound. c. Disconnect set from battery, remove cover, check valves are properly seated. Remove valves in turn, and clean pins with soft (old!) toothbrush. |
| Fault 3. Radio fuse keeps blowing. | Rectification a. Check that the fuse is the correct one. Do not be tempted to fit a higher rated one - if the correct fuse keeps blowing there is a fault with the set or its installation. |
| Fault 4. Polarity. | Rectification Many valve radios were not polarity conscious, part-transistor sets were however. A set that has been connected the 'wrong way will almost certainly need one or more replacement diodes or transistors, and unfortunately there is no way that this can be detected until the set fails to function and the above tests have been tried. |
| Fault 5. Noisy switches and controls. | Rectification Crackles and other unwanted sounds when adjusting volume and tone controls are almost always caused by dust or dirt build-up on the contacts. They can usually be eliminated by squirting a drop of WD40 into the 'pot' body. The same trick also improves wave change switches. Try it if there is excessive crackling when changing waveband, or if one band is significantly quieter than another. Disconnect the set first though! |
Most components for valve car radios can still be found without too many problems; I can supply valves, vibrators etc. in cases of difficulty. The problem, as already stated, is with the trim parts such as knobs and switch buttons etc. When looking for period radios in autojumbles and sales try to find one that is complete. Don't be too concerned if the radio looks tatty; if all the original parts are present this can be rectified.
