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Cobra 25 Nw ltd classic won't turn on?

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Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Wednesday, 12 May 2010, 21:44 PM

hi i got a cobra 25 nw ltd from a buddy of mine to work on, he said, "i plugged it one day it turned on and worked fine, and then the next it wouldnt turn on" i tried different power cords and all, i got a suggestion that the diode on the inside of the radio might be bad, the one thats soldered to the power connector, the radio is only from 07' so it should be working great never been tuned or nothing, and is in great shape, any body experience this? :|
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by 715minigrass » Wednesday, 12 May 2010, 22:20 PM

Must be that diode.

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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Thursday, 13 May 2010, 6:09 AM

yea thats what i was thinkin but i wanted to get some input befor i go forth with it
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by Night Crawler » Thursday, 13 May 2010, 7:31 AM

Does it blow the fuse in the power cord when the power supply is turned on?
If it doesn't the diode isn't shorted check it with a VOM before it's replaced.

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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Thursday, 13 May 2010, 15:16 PM

no i just plug it in, and wont turn om, whats a "vom"? pics?
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by Night Crawler » Thursday, 13 May 2010, 15:40 PM

audio boy wrote: whats a "vom"? pics?

Volt Ohm Meter
http://www.wikipedia.org/wiki/Multimeter

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Re: Cobra 25 Nw ltd classic won't turn on?

Post by headhunter1 » Friday, 14 May 2010, 23:03 PM

eather a loose wire on the on and off switch or prob a burnt trace on the back side of the board i have see the diode blow and get the yrace as well

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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Sunday, 16 May 2010, 9:35 AM

wonder what kind of diode it is, and what kind of ohms i should check for?
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Monday, 17 May 2010, 9:01 AM

what should i check for on the vom?
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Monday, 31 May 2010, 19:24 PM

Ok it does make my power supply shut off, can sombody please tell me what kind of diode this is in my cobra 25, is it called a polarity diode by chance, please help soon, or im gonna have a unhappy customer,
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by Night Crawler » Tuesday, 01 June 2010, 7:25 AM

audio boy wrote: can sombody please tell me what kind of diode this is in my cobra 25
It's a 1N4003 marked on the board as D17 the reverse polarity protection diode.
http://www.radioshack.com/product/index.jsp?productId=2036269

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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Tuesday, 01 June 2010, 12:20 PM

Any general area were its located, thanks alot night crawler for your help.
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by Night Crawler » Tuesday, 01 June 2010, 12:44 PM

It should be on the circiut board in the back of the radio where the power cord plugs in.

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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Tuesday, 01 June 2010, 13:16 PM

ok i found it it doesnt appear to be burnt up, o and one other thing the negative wire coming from the pwoer plug to the board, pokes threw a hole in the board with solder around it but its not soldered, when i touch it to the solder it shuts off my power supply any idea whats up?
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by Night Crawler » Tuesday, 01 June 2010, 13:36 PM

audio boy wrote:ok i found it it doesnt appear to be burnt up,
That doesn't mean anything the diode still could shorted and it won't show any sign of being bad.
headhunter1 wrote: prob a burnt trace on the back side of the board i have see the diode blow and get the yrace as well
Thats what I'm thinking.
audio boy wrote: one other thing the negative wire coming from the pwoer plug to the board, pokes threw a hole in the board with solder around it but its not soldered, when i touch it to the solder it shuts off my power supply any idea whats up?
After what you described I think it took the trace out that's why it doesn't looked like it's soldered it should be. If the diode is shorted when you touch the negative wire to the solder trace it will shut the power supply down.Check the positive wire also for a loose or unsoldered connection.

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Re: Cobra 25 Nw ltd classic won't turn on?

Post by audio boy » Tuesday, 01 June 2010, 14:45 PM

will a burnt trace be very noticeable because everything looks fine to me
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Re: Cobra 25 Nw ltd classic won't turn on?

Post by Night Crawler » Tuesday, 01 June 2010, 16:02 PM

audio boy wrote: everything looks fine to me
If a wire is poking through a hole in the circuit board and is not soldered to it that's a problem. If the diode shorted it could of got hot, possibly causing the negative wire to lift from the trace.
Without looking at the board and testing the circuit it's hard to tell you what the problem could be.


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