Thanks to all you good folks for your imput with this problem last week. Since then I have discovered that if I jiggle the antenna lead at the back of the radio, and don't push it in all the way, I can get good reception.(Improper contact?) However, when I have the engine running there is a lot of "popping" and interference. I understand this may be comming from the alternator and there is a device that will help with this. Any thoughts? I also still cannot get anythig but static on the FM dial and continue to look for input. Thanks, Randy
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Re: 64 DELCO RADIO PROBLEMS REVISITED
Randy, if you have the AIM, go to the section for the AM/AM radio ooption, U69.
Take a look at the pages on grounding straps and on Capacitors. Ensure you have them all installed. There are 8 capacitors.
Harry -
Re: 64 DELCO RADIO PROBLEMS REVISITED
That was AM/FM and the U69 radio option. I should use my spell check.
HarryComment
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Not an unsusal finding....
The antenna lead-in wire makes a dramatic right-angle bend at the bananna jack that inserts into the rear of the radio chassis. The center conductor is hair-thin wire that's easy to fatigue fracture and this is especially true of cars that just had an interior restoration and the carpet was replaced (generally winds up moving, pushing/pulling on the radio antenna lead-in wire).
If the lead wire is internally fractured RIGHT AT the bananna plug, you've got a 'stub' of wire that's 'pointing' DIRECTLY at the firewall and despite the lead-in wire's shielding, you can expect to pickup engine noise like gang busters.... That's the reason all Corvettes had the radio antenna mounted on the rear fender (move it AWAY from the engine compartment despite the underhood shielding components).
Your test here is do go to Wal-Mart, buy an el-cheapo radio antenna with captive lead wire and substitute it for your exisiting lead-in wire + antenna. Expect to hear running engine noise UNTIL you have a helper walk the antenna out of the cockpit back to toward the rear of the car; engine noise should fall dramatically.
If she works well with the substitute antenna, it's time to peel up the carpet and replace your existing lead-in wire (Paragon and other catalogs) and be CAREFUL when routing it not to overstress and break it.
Once you get solid AM reception, it's time to work on the FM problem. Inside your radio, two separate tuner circuits look out through a common antenna. The FM demodulator is very INSENSITIVE to antenna integrity. It's optimization only really comes into play when you're in a fringe reception area. In a major metro area you can expect to pull in solid FM reception with very little in the way of an antenna.
AM broadcast is very SENSITIVE to antenna integrity. So, if you're getting good AM reception after your troubleshooting and you still aren't getting FM, it's time to pull the radio and question the integrity of its internal circuitry.Comment
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Re: Not an unsusal finding....
Thanks for the suggestion Jack. I did just that and bought an el cheapo antenna, hooked it up and walked it to the back of the car but still have a lot of popping and crackle. No FM reception at all, or extremely weak at best. Eckler's sells an item to reduce engine noise caused by the altenator. Any idea if this works??
Thanks,
RandyComment
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Re: Not an unsusal finding....
A myriad of 'hush up' capacitors were installed on radio equipped cars. Interference can be either conducted (down the power line an into the radio through its power supply) or radiated (airborne and picked up by the antenna). Knowing where to look for problem(s) is an art form--one that's assisted by knowing whether the interference is conducted or radiated.
The fact that you connected a secondary antenna, walked it to the rear of the car, got AM working, but still heard ignition noise is telling you a few things....
First, since FM didn't spring to life, it's telling you the radio has internal problems. You should pull it and have a trained tech bench test/repair it. Could well be the susceptibility to engine noise is a collaterol consequence of internal problem(s).
Second, with an aux antenna properly relocated to the rear fender area, you should have STONED typical radiated interference. This stongly suggests the problem is an engine noise conduction issue. One cap that was installed to thwart this attached to the radio's branch circuit power supply lead wire as it passed by the instrument cluster.
Short of checking for the presense of all the original radio RF protections (shielding components and specific capacitors), there's little a novice can do. Just because a given capacitor is there (installed) doesn't mean it's in good working condition.... They can age and begin to leak (essentially a form of 'short circuiting') and one needs the ability to test the part BOTH for its specific storage capacity as well as its leakage profile (dissipation factor).
The aftermarket noise filters that are sold (you can also get 'em at Radio Shack) are a form of 'boat anchor'.... They're typically a pretty healthy RLC filter intended to be installed on the power line serving the radio to 'knock down' or block the passage of electrical AC waveforms much above DC.
Sometimes this is the easiest/fastest way of curing a conducted noise problem as the other approach involves analyzing the circuit (an oscilloscope is handy) and walking back upstream to find the faulty or missing component(s) that create the problem in the first place.
But, since you already know there's something Rotten in Denmark inside the radio (FM isn't operable), I think I'd start there.... It needs repair anyway and whatever is wrong just might be contributing to your noise susceptibility problem to boot....Comment
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