Diode for reverse polarity protection

If it's a reverse protection diode across the power supply, it ain't your problem. More likely, you fried the supply when you shorted it out with the diode. mike

Or just the power supply is inadequate to the task, assuming it is a replacement.

Mark Z.

The diode is ok.

You might want to give us the model number of the scanner. Many Uniden scanners use REGULATED power. It could be that when loaded by the speaker and display light, the AC adapter no longer provides the needed voltage.

My BCD396T uses a 6vdc 800mA REGULATED adapter. I don't think the use of the 1N4001 is your problem. I think that a) the AC adapter was damaged by the incident, or b) the scanner was damaged by the incident.

The scanner is a BC780XLT. Today ,after work, tried turning the scanner on and got the same response, the backlight blinked and I heard a pop in the speaker. I unplugged the speaker and the turned the scanner on. The display and its backlight came on and it started scanning. I plugged a remote speaker into the jack on the back panel and got audio. I disconnected the remote speaker and plugged in the chassis speaker and it produced audio. All the scanners functions are now working normally. I figure the new diode is right and I know the power supplies, both the 12V and the AC adapter, are good because they work on an identical scanner. For now I'm going to leave it alone and if I have more problems I'll check my soldering work. Thanks for all the responses.

There are two kinds of reverse-polarity-protection diode. Or, rather, two arrangements for them. One has the diode in series with the device, so if you connect it wrong the device simply won't energize. The problem with this is that the diode drops about half a volt, and that's a big chunk out of a 12v source. So for car stuff what they do is to jump the diode across the power line. That way, if you connect the power backward, the diode will conduct and blow the fuse. If there is a fuse. Otherwise, the diode burns up, smelling like you've just burned up the Lord's original microprocessor. If you remove the diode completely, the device will work once again, but there will be no further protection.

Ergo, it's easy to get confused with these things. Back in the days of Kinsler Hi Fi Service I'd connect a diode in series with the power supplies of CB radios that I thought would be receiving abuse. The performance would suffer only a bit, and the device would keep working.

M Kinsler

delighted to be out of that business

This sounds like the power supply is not adequate, or has a failure, thus causing too low a supply current.

If you put your volt meter across the power supply output while running the scanner, and if you see a dip in the voltage, you will know for sure that the power supply is not proper. You can also do a current test to see how much the scanner is pulling. Refer to the service specs to see what the maximum current pull is for your scanner, and then compare to know if there is a fault.

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JANA _____

The scanner is a BC780XLT. Today ,after work, tried turning the scanner on and got the same response, the backlight blinked and I heard a pop in the speaker. I unplugged the speaker and the turned the scanner on. The display and its backlight came on and it started scanning. I plugged a remote speaker into the jack on the back panel and got audio. I disconnected the remote speaker and plugged in the chassis speaker and it produced audio. All the scanners functions are now working normally. I figure the new diode is right and I know the power supplies, both the 12V and the AC adapter, are good because they work on an identical scanner. For now I'm going to leave it alone and if I have more problems I'll check my soldering work. Thanks for all the responses.