On Jun 13, 11:00 pm, Ramset wrote:
On Jun 13, 2:09 pm, UCLAN wrote:





Ramset wrote:
I fried a diode used for protection in a Bearcat scanner. It was fried
by connecting the wrong power cord (reverse polarity) into it.
The AC adapter puts out 13.8VDC and 700ma. I tried replacing it with a
IN4001 and it powered up the display and started scanning. However
when I plugged the speaker and display light back in it didn't seem to
have enough power to start it all up. The display flashes once and I
hear a pop in the speaker but that's it. The original diode had
markings printed which I think was RA above VB.
Any suggestions on another diode to try?

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.

--
GO ALINGHI! Beat the Kiwis.

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.- Hide quoted text -

- Show quoted text -

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