DIYbanter - View Single Post - polarity of power cord

zirath

Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$Yy2.1091@trndny04...
We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from ebay.
It didn't have a power cord. It says it's a 12v dc 2.5a but it doesn't
give the polarity. A person from gateway said he thought it wouldn't hurt
the monitor if it got plugged in backwards but I'd rather not try it.

Would appreciate any help.
If it has got any external metal parts such as RCA (phono) connector outers,
BNC connector outers, 'D' connector surround etc, or possibly screws for a
stand, as these often go right through the plastic case, and into the
internal chassis, then try measuring from any such metal to each of the DC
power input connector's terminals in turn, using an ohm meter. Chances are
you'll find a direct connection, and that will be your DC ground ( "-" )
connection. The other will then be the "+". Assuming that it's a 'standard'
co-axial DC connector, on most modern equipment, 'pin' is "+" and side
contact is "-" although that's not cast in stone. Be aware when you are
obtaining a replacement PSU, that the plug is often a slightly abnormal
size, being a little larger than those you typically find on 'general' power
supplies. Also, make sure that you get one well rated for the job, as these
monitors do draw quite a lot of current, and may well surge up close to the
quoted 2.5 amps at startup, as the LCD backlights first fire up before
settling to their run current.

As to whether it would be safe to reverse connect it, I wouldn't like to
say. Some equipment is perfectly well protected against such 'consumer
antics', but it is by no means guaranteed, and if it is not adequately
protected, the result is often an item that's fried beyond repair, for no
other reason than unobtainable power supply devices, as many previous posts
on this subject over the years, will attest ...

Arfa

The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.

Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -

The adapter symbol shows center + and side -. It is labeled 12vdc 4a.
The monitor is 12vdc 2.5a so the adapter should have enough power.