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How to replace a protection diode in a 76xl uniden

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  • Cobra Master
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The same way you took it out. make sure the arrow is facing the right way.

Posted on Nov 25, 2014

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Posted on Jan 02, 2017

One Wire
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SOURCE: power was reversed now radio keeps bowing fuse and will not come on

Most cb radios have protection diodes that are made to burn out to save the radio in this situation. Usually you can replace them with a rectier diode between 1n4004 and 1n4008. They can be purchased at Radio Shack, or if you need more stuff, you can get them from Parts Express. This unit is the same as a cobra 29. If the pc board layout and numbering is the same, then the protection diode number is D23, which is located in front of the pa speaker jack on the main pcb. If you need more help, feel free to email me at

Rollin CBs

Posted on Jan 26, 2008

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Magnum s3 locate the protection diode

If you are saying that the device wont power on because the polarity was wrong and now it blows the fuse all the time when hooked up, that would be the reversed power connection protection diode. If you take the unit apart, look where the wires come into the case and connect to the main board. There is an axial lead black cylinder device that is 3 mm thick and has a silver band around it. That is the diode that you are looking for is d93 in the upper right of this diagram

Jun 26, 2014 | Uniden PC78ELITE 40-Channels Base CB Radio

1 Answer

I need to know ! How do I make my Maxon MCB 45W Louder ....What do i have to do in my radio to make my transmit louder....Thank you!

I know you don't want to hear this, but the Maxon radio you own, and many similar radios (Cobra 19, Midland CB-1, Midland NT-CB-1001LWX, Uniden PRO-505XL, etc) are on the bottom of the performance list. These are for those who just need a crappy radio for the summer time traveling, and about keeping the cost as low as possible. Here are a few of my favorites that have good-LOUD audio: Galaxy, Connex, General Lee, and some of the older Uniden radios like Grant XL, PC-76XL or older Cobra 29 LTD, 25 LTD models.
Please stay away from Stryker radios, Magnum radios, Northstar radios and any radio which has a NITRO-KNOB. These are ticking time bombs. In other words, they WILL fail and it wont be an easy fix either. Most Strykers and Magnums have PCB Chip failures. They are next to impossible to replace. And finally, don't be so quick to buy the pretty radio with all the flashing lights either.

Mar 21, 2013 | Radio Communications

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How to replace a meter in a uniden 76xl

its a snap in with only two wires--if now not working it may or may not be the meter itself.

Apr 12, 2012 | Radio Communications

1 Answer

Crossed power wires on uniden c b radio

Remove the top, the red wire is + and the black - there should be a small black diode near by, if the wires were crossed the diode is shorted and must be replaced "part of the protection circuitry" check for any open foils on the circuit board, If you are very lucky the unit will come back online.

Mar 07, 2012 | Uniden Bearcat Pro PC78LTW 40-Channels...

1 Answer

Can anyone please help me with my superstar red 3900 has i have changed the audio chip and protection diode and i have still got no recieve what could the problem be thanks

No RX or No Audio?

Could be blown protection diodes or if no audio a faulty capacitor close to the audio chip!
The protection diodes can blow if you were close by someone with a high power transmitter, then the diodes would blow kinda like a fuse to protect the rig, result no RX symptom!
Replacing the diodes will cure that problem, located close to the rear of the rig.

Sep 06, 2011 | Superstar SS-3900EGHPA CB Radio

1 Answer

My Uniden UM525 is blowing fuses the instant I plug it in. I don't know what happened to it but I'd like to fix it. If anyone has any ideas I'd love the assistance. Thanks in advance,

Hey Marked,

First check the diode in the B+ line . Probably it is shorted due to a reverse polarity connection.

Take it out and test without the diode if it works replace it diode.

Good luck.

Aug 06, 2010 | Uniden UM525 ES Series VHF Radio with...

1 Answer

Blows fuse when you plug power in, it is not

Make sure you're connecting the radio with the proper polarity. There is a protection diode inside that will cause the power supply fuse to blow or go into overcurrent shutdown if you have + and - reversed. It's also possible this diode has been shorted. You can't tell by looking at electronic components (unless they are physically damaged) whether they are good. An ohmmeter can be used to test for shorted diodes. Look at the board where the power leads connect for the diode.

Mar 12, 2010 | Uniden PC68XL (40 Channels) 2-Way Radio

1 Answer

I have a Uniden 76xl. It was putting out about 7 watts and I added a rfx 75 kit. I used the instructions for 78 series radios, to the letter. The radio was stock and everything was intact...

D8 is a polarity protection diode. you have hooked something up incorrectly. I would go over what you have done, and do not try using the radio until you fix it. If you haven't already, you are going to have to replace D8.

Mar 03, 2010 | Uniden PC78ELITE 40-Channels Base CB Radio

1 Answer

Blown fuse and reverse polarity diode

Check around the pcboard where the dc goes to the board, sometimes the foil will burn. Also chec the transformer, Chec that one of the wires did not come off the plug in the back. When you replaced the protection diode did it blow again? If not keep checking for opens on the pc board. When you said it was dead do you mean no lights at all or no tx and rx?

Jan 26, 2009 | Uniden GRANT LT 2-Way Radio

2 Answers

Power was reversed now radio keeps bowing fuse and will not come on

Hello hubcap,


When the power was reversed this shorted out one of the components, possibly an Operational Amplifier. This tells me that there is no diode protection and possibly the circuitry is exposed directly to the input power supply. The fix would be to find the shorted component with the use of a schematic and a multimeter. Once you correct the shorted component then if possible you can add diode protection by putting a diode (forward biased direction) in the path of the positive line.


Again you will need a schematic, and a multimeter to work on this problem.


I hope this helps,


Thank you,



Oct 12, 2007 | Uniden PC78ELITE 40-Channels Base CB Radio

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