Question about Cobra 29 LTD CB Radio

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C.b.radio-power won't come on.(red & black wire show short!)

This unit has been probably unhooked from coax& keyed-up,or hooked up to battery wrong.(pos.&neg. switched). Red & black wires show continuity. Can you point me in the right direction to find the "short"? Thanks, markhopkinsjr47@gmail.com

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Hi,
The fault is probably at either end. Yes, it could have been reversed, but most radios are easily protected against this.

If you are getting no lights or anything when keying mic, then there may be an inline fuse along the cable. As you are getting continuity, open the case up, and look for any evidence of heat at the components nearest the power supply - particularly the protection diodes - Black cylinrical components with a silver band.

You really need a meter or scope to go in much further, and check supply voltages between components and -ve, and downloading a copy of the circuit diagram will help this.

The other main fault is usually the output power transistor - which needs a sink for all the power getting thrown at it. If you remove the antenna, it can quickly overheat and fail.
Both components can be checked in-situ for voltage (or not) but the output can only be tested with a scope.

Of course - the "on" light could have blown, so may be functioning without indications, - but I doubt it.

Also check Mic outputs on the plug to make sure that is working. Some units won't function if this is disconnected.

Posted on Jan 08, 2009

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