Polarity of AC Adaptor

there is no polarity in ac current as ac means alternating current and that means alternating between positive to negative back to positive back to negative and so on
only dc ( direct current ) and the center pin of the plug is designated as the positive pole has polarity, the outer case being the negative
OR Are you asking the voltage of the ac adapter and the voltage of the dc output side of the adapter

four things to consider while purchasing a replacement
1.voltage--we know its 12 volts DC
2.wattage-- your monitor uses 80 watts - this will take a ac adaptor with about 1 ampre
3. polarity of the adaptor- the inside tip of the adaptor cord needs to be the same polarity (posative or negative) as the plug it's going into. there should be a little insignia near where you plug the adaptor into the monitor with a partial circle and a line going to the middle of the circle, each having a plus or negative sign. the line that goes to the center is the inner cnnection (refered to as TIP)
4. size of the tip - dont accept any plugs that fit loosely as they will cause problems down the road.
If you have the old adaptor, you can carry it down to radio shack and they should be able to match it up for you. If not , print these specs and carry them in with you when you go----
here is the page showing the power specs available http://www.ciao.com/Max_Displays_MD_219__15408106#productdetail

how to video on using a meter

I know this thread is old, but it came up in my search for similar issue. I own a Banshee 2. Make no mistake, this thing eats electricity because it has an internal Amplifier (you can use it as a practice amp if you connect a regular speaker in the correct hole). And the 9v supply MUST be AC (most pedals are DC). No ordinary power supply will work and may damage your Banshee. You must have 2000mA (or more), 9 volt AC power supply. It may be described as 9VAC, 2.0Amp or similar. Do not try a DC power supply. The plug and socket are an unusual size, probably to stop people sticking 9vDC into it. I've attached a picture of my own power supply that works great. About £7 ($10 USD) of ebay.

Here is how you might check the polarity of a 7.5 volt DC replacement adapter:

Put the 5 batteries into the unit and verify operation. NOW using a DC voltmeter measure the voltage from battery negative and meter negative connected and meter positive to the pin on the power jack. IF you see 7.5 volts positive, then the pin is the positive lead for the adapter.

If you see zero, then continue testing.

With the 5 batteries inserted, connect the positive meter lead to the positive of the stack of batteries. Now touch the negative meter lead to the pin.
If there is 7.5 volts there, then the pin is the negative lead for the adapter.

READ THESE INSTRUCTIONS CAREFULLY.

USUALLY the jack has a contact that disconnects the batteery when the plug with sleeve is inserted.. We are testing the jack without inserting a plug here so the plug should HAVE THE BATTERY VOLTAGE with correct polarity on the pin.

You should go to a local electronics shop with the old adaptor.
They merely need to match: Voltage in Voltage out Current requirements Plug size Plug polarity (center positive or negative) There is nothing "magic" about the original vendors power adapter.

i'm guessing you don't have the original adaptor to test it... sometimes polarity is printed onto the case where the adaptor plugs in... get out your magnafying glass to see it tho.

If I understand your description correctly, you have two TVs that use the same model adapter, and both adapters have failed. In that case, I would suspect a weak design, or you may have put them in some place where they were overheated or zapped by power line surges. If it appears to be a design problem, you may want to consider using a substitute.

The adapter should have the output voltage and current marked on it, for example, 12VDC 2300mA would be a 12 Volt, 2.3 Amp output. The polarity is usually marked with a diagram showing whether the center in or hole in the plug is positive or negative.

You can use an adapter with the same voltage and plug style (including polarity) and the same or greater current output. If you find one with the right voltage and current, but the wrong plug, you may be able to change the plug. Just be absolutely certain you have the wires going to the correct terminals; reversing the polarity could damage or destroy your TV. Do a proper solder job on it; simply stripping the wires and twisting them on will not be reliable.

Sources for adapters include www.jameco.com and www.mouser.com.

Hi,

I have uploaded the GPX PDL705 manual to this site today. If you check tomorrow they may have posted it by then.

If you look at the small print on the adaptor it should indicate by diagram Voltage output, current capacity, type and tip polarity by small diagram. Most adaptors are 'positive' -- but if you are unsure do not plug the adaptor into the device because it will fry it!

oh no maybe you used different adaptor some adaptor have reverse polarity. check the adaptor before plugging it..if you using variable voltage set to 3v then adjust also the polarity. the polarity should match the polarity of your camera.