| Author |
Message |
    
Jchapman84
New member
Username: Jchapman84
Post Number: 1
Registered: 11-2008
| | Posted on Thursday, November 13, 2008 - 8:43 pm: | 
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I've got a cobra 29ltd (old one with side mic jack) that won't power up. I've got power through the protection diode. Where do I start looking? Are there any common things that go out on this radio that I should look at or is it pretty much get the schematic and start going through every component? |
Hotwire
Senior Member
Username: Hotwire
Post Number: 2671
Registered: 1-2005
| | Posted on Friday, November 14, 2008 - 8:41 am: |
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If the protection diode has been replaced and put in backwards I believe it would not work. You should check for broken traces and cold solder joints also.
I have a very old Cobra 19, the first cobra 19 in production from way back. Sometimes when I turn it on nothing happens. I switch the volume/on off switch off and on a few times fast and then it comes on. Could it be that maybe the on off switch is getting worn? Try playing around with that, switch it off and on repeatedly and see what happens. Besides that looks like your gonna need that schematic.
Kenny
CEF491
Reading the mail around Indianapolis Indiana!
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Jchapman84
New member
Username: Jchapman84
Post Number: 2
Registered: 11-2008
| | Posted on Saturday, November 15, 2008 - 11:31 am: |
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I'm getting power through the on/off switch until I removed one leg of the diode, so I think they're ok. I poked around and found power on a few other points on the board, so I think its time to drag out the schematic...dang it! this is gonna take a while. |
Jchapman84
New member
Username: Jchapman84
Post Number: 4
Registered: 11-2008
| | Posted on Monday, November 17, 2008 - 6:22 pm: |
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ok, so I started trying to trace, but found out that the whole thing is hot! even the case and both parts of the antenna jack. I can't find anything that doesn't have voltage. Any Ideas? |
Drzuo
Member
Username: Drzuo
Post Number: 62
Registered: 1-2006
| | Posted on Tuesday, November 18, 2008 - 9:42 pm: |
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Hmmmm. what are you grounding the multimeter to? if its connected to ground on the radio, even if there is a direct short to ground, you should read zero volts, as there is no difference of potential between the multi meter leads. Also a direct short to ground would ask the power supply to produce a near infinite amount of current, which should pop the fuse or breaker in the power supply. Is there any voltage drop from these "hot points" as compared to the power supply (ie power supply is 13.8 volts, chassis is 12.5 volts etc?) Could be a cap or diode that connects to ground through a resistor is shorted? (that could limit the current and keep the power supply from going into protect mode) It's an interesting problem. |
Jchapman84
New member
Username: Jchapman84
Post Number: 6
Registered: 11-2008
| | Posted on Monday, November 24, 2008 - 7:24 pm: |
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I grounded the meter to an extra lead I had coming from the power. Do I need to test grounded to the chassis? There are some points that have small drops in voltage, the chassis being one of them. I can find them again and write them down if that would help. |
