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Cobra 200GTL DX issues

B

Beakster

Member
May 27, 2008
14
8
13
Hi,

Got some problems with my rev3 Cobra 200 which has been working great for the last year.

Sometimes when I turn it on nothing happens for a few seconds, then it turns on. Then when I key the mic on high power the frequency counter and lights on front flicker on and off really fast and I can hear the relay clicking away on and off in quick succession.

This sometimes happens on low power too. If I keep trying to transmit then occasionally the radio sorts itself out for a time, but other times it gets worse. When this happens the lights on the front start to dim, and the go out all together, so it looks like the radio is off but I can still hear it receiving static.

The radio is about a year old, but the warranty is void because about 5 months ago it received reverse polarity (jump starting car) and I had to open it up to replace the idiot diode.

I am competent in soldering (although not surface mount) and would like to fix this myself. I just need to know which component is faulty. Any suggestions?

Thanks
-Chris
 

Im thinking that reverse polarity caused havoc in a voltage regulator aswell. That jumpstarting cars can cause alot of problems in vehicles alone one way to kind of help is to run your jumper cable negative or the black jumper to metal or a ground not straight through the battery.
 
Hi,

Thanks for the replies.

I'll check that voltage regulator.

The thing is that it was working fine for 5 months after the jump starting incident, so this may be unrelated.

I don't want to send it to the Cobra repair centre because I'm in the UK so postage wont be cheap and I'm not sure they will fix it under warranty given the scorch marks on the board where the idiot diode blew.

Cheers
-Chris
 
i would open it up and look for bad power connections or power connections that were damaged when the radio was reverse polarized. just because it recently started this behavior does not mean it is not related to that incident. you'd be suprised at how many times we have seen a past event cause other problems down the road.

also, the symptoms you list sounds as if there is some kind of high resistance on the dc rail. especially the fact that it sometimes works in low power but will not in high power. high power consumes more current, and if there is a high resistance it can not get the current it needs and the radio will choke, sputter, dim, and go on/off like you listed. this high resistance could be from a faulty connection, or even a trace that was damaged from the high current flow that existed when the radio was reverse polarized.

you really should remove any electronic connections that go straight to the battery before jump starting. we have to repair units in police cruisers (cameras, mdt's, radios, etc) often when they jump start them without removing the fuses. there is a big votage spike during this brief time when the jumper cables are first placed on the battery.
 
ss8541 said:
also, the symptoms you list sounds as if there is some kind of high resistance on the dc rail.
Click to expand...

You were right! I've now solved the issue! After lots of messing about I finally found the problem was the fuse which is in the radio's power cable to the battery! I knew the fuse hadn't blown because my multimeter was showing over 12V at the radio, but when I opened the little fuse holder I saw that the fuse had melted into a blob!

I replaced with a new one and the Cobra is good as new again! :) I guess the melted fuse was allowing the voltage through but not enough current or something. Thanks for the advice. (y)
 

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