I'm looking to follow your directions in cutting the glass diode...I only see one that looks like glass. But, on the board it says D-12, not D-11. It's under a bunch of wires. and I don't see how to cut it. First, I need to know if that's it ?
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Re: Cobra 29 LTD CLASSIC C.B.
You should not cut the modulation diode, you should adjust the potentiometer VR-4 for full modulation. By cutting the diode, you risk over modulating. By turning up the pot, you can correct for an over modulation.
If you are still insistent on cutting the modulation limiter, it is D11, located directly in front of VR4 and C73. Looking at the radio from the front to back, it is in the right corner, apx 2 1/4" from the back and 2 3/8" from the right side.
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Yes, if you have a meter check resistance (like reading a fuse) with the radio off and power cord removed.
Only two of the three pins (look at power cord to see only two have metal in them) are used.
With power switch on front in off position there should be no reading across the + to - pins on the back of the radio.
If a short there the protect diode is shorted--likely first time it got hooked up backwards--easy to do.
Follow in this case the + pin on back just inside the radio and it goes directly to a diode. cut the diode if a short there and read again at the plug--if short gone replace the diode--radio will work without it but you will have no protection in that case.
If it is the original 29 LTD, D11 is a IS2075K Diode. Attached is a section of the schematic showing the diode. Check the components connected to it to verify if they match those on the schematic section below. If they do, you should be fine installing the listed Diode. If they don't you may not have the model of Cobra 29 listed below.
Hi, my name is John. Welcome to FixYa. Take the cover off circuit board side, and with the eraser end of a pencil, touch around on the board trying to locate cold solder joints, have to look real closely and re-solder them....Thanks for choosing FixYa...John
there is a diode on the power line that blocks the dc to ground. follow pwr wires down to board. and the first diode on the + pwr is it. this is on all radios. and not just cbs. just put a new diode on the back side of the pwr plug. were the wires solder onto. but even better what we do @ our shop 254.718.4042 is use or make bridge rectifier install inline. and you will never have that problem either direction you plug it in. will work. no more worries about polarity.