Hey all mI was just looking for some ideas on a cobra 2000 recieve problem that my buddy has with his spare radio. The problem is that the recieve is really week or low. I am just looking for some ideas from you all on where to start with looking for the problem. I know Ive seen there was a few other people in the past that had been through this same dilema. The radio deffionately has a problem though its not as good on the hearing as it was so something is wearing out. Thanks to all that help......Tony
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Cobra 200GTL recieve problem
- Thread starter TonyV225
- Start date
Ideas? Sure.
1) Damage: If the radio was left connected to an antenna during a storm, lightning need not strike your antenna to cause damage. It can hit a tree or utility pole across the street and pump a big surge into a nearby antenna. Kinda like having a 10 kW mobile pull into your driveway, and key up 50 feet from your antenna. Hard to pin down without a signal generator and scope.
2) "Golden Screwdriver" syndrome: Somebody with his tunnel-vision focused on a wattmeter keys the radio and turns each tuning adjustment in the radio, one by one. The ones that don't make the wattmeter change are ignored when he turns them. He also ignores the setting of that screw before it was turned. The result is a lot of receiver adjustments all out of whack.
3) Age. The oldest radios of that model were made before 1980 in Japan. Some batches of that radio (mostly Taiwan production) will have failed capacitors INSIDE one or two of the slug-tuned "cans" that contain RF/IF coils/transformers. Only way to tell is to do a normal alignment. The tech watches for slugs that don't peak at their normal (approximate) positions. Biggest clue is when one of the tiny black slugs appears to peak with the slug DEAD FLUSH with the top of the can. Typically, this delivers a broad, gradual "peak" from an adjusment that normally has a "SHARP" peak, one that drops off a lot with only a quarter-turn on the tool, either side of the peak. A slug that doesn't "peak" normally is a clue that the (a) problem is in that circuit, somewhere. Maybe the tuneable "can", maybe an adjacent part that feeds into or out of that one. A perfectly good IF transformer that feeds into a shorted transistor will act this way, too. Even if you find a really clear-cut failure like this, it may or may not be "the" problem. Could be more than one.
Trouble is, without the experience of aligning the first couple or ten dozen of that radio, how do you know which slugs exhibit a sharp peak, and which ones don't? The brightly-painted adjustments with the larger hole in the can are an example. A couple of them have a VERY broad, gradual 'peak' when they are adjusted, even when the radio is performing perfectly.
And if you can't get your hands on a signal generator, aligning a receiver will be a lot like holding a broom upside-down with the handle in your upturned palm. With experience and practice, you could, mostly. The less practice you have, the more you need a steady, predictable "test" signal.
A pro will probably "check" the alignment first, before looking for defective parts. Like I said, the behavior of the tuning slugs will point to other problems, if there are any. Aligning a receiver first is a diagnostic procedure.
73
1) Damage: If the radio was left connected to an antenna during a storm, lightning need not strike your antenna to cause damage. It can hit a tree or utility pole across the street and pump a big surge into a nearby antenna. Kinda like having a 10 kW mobile pull into your driveway, and key up 50 feet from your antenna. Hard to pin down without a signal generator and scope.
2) "Golden Screwdriver" syndrome: Somebody with his tunnel-vision focused on a wattmeter keys the radio and turns each tuning adjustment in the radio, one by one. The ones that don't make the wattmeter change are ignored when he turns them. He also ignores the setting of that screw before it was turned. The result is a lot of receiver adjustments all out of whack.
3) Age. The oldest radios of that model were made before 1980 in Japan. Some batches of that radio (mostly Taiwan production) will have failed capacitors INSIDE one or two of the slug-tuned "cans" that contain RF/IF coils/transformers. Only way to tell is to do a normal alignment. The tech watches for slugs that don't peak at their normal (approximate) positions. Biggest clue is when one of the tiny black slugs appears to peak with the slug DEAD FLUSH with the top of the can. Typically, this delivers a broad, gradual "peak" from an adjusment that normally has a "SHARP" peak, one that drops off a lot with only a quarter-turn on the tool, either side of the peak. A slug that doesn't "peak" normally is a clue that the (a) problem is in that circuit, somewhere. Maybe the tuneable "can", maybe an adjacent part that feeds into or out of that one. A perfectly good IF transformer that feeds into a shorted transistor will act this way, too. Even if you find a really clear-cut failure like this, it may or may not be "the" problem. Could be more than one.
Trouble is, without the experience of aligning the first couple or ten dozen of that radio, how do you know which slugs exhibit a sharp peak, and which ones don't? The brightly-painted adjustments with the larger hole in the can are an example. A couple of them have a VERY broad, gradual 'peak' when they are adjusted, even when the radio is performing perfectly.
And if you can't get your hands on a signal generator, aligning a receiver will be a lot like holding a broom upside-down with the handle in your upturned palm. With experience and practice, you could, mostly. The less practice you have, the more you need a steady, predictable "test" signal.
A pro will probably "check" the alignment first, before looking for defective parts. Like I said, the behavior of the tuning slugs will point to other problems, if there are any. Aligning a receiver first is a diagnostic procedure.
73
I read up lastnight and came up with the idea of bad caps. Tom the owner is doing just as justin described I have a feeling its a cap or caps most likely. That radio is his original first Cobra 2000 and it is old so tahts my guess. It wasent a lighting strike or any sort of side flash so from the radio sitting do to him running some of his other 2000s or other radios it just went on the fritz thanks both of you......Tony