Measuring voltage in AC adaptors

[acharris]

Hi all, I need some advice. I am trying to measure an sega game gear ac adaptor to see if it is working or blown with a multi-meter. I can't get a reading on it. I measure a Master system adpator and get a reading on it, like wise when I measure my universal adpator. But no luck on the sega adapter.

 

Also I tried to measure a NES/SNES adaptor and I can't get a reading on it either with the meter. So I try a working SNES adaptor and also can't get a reading on that. Is there someway to measure these voltages with a meter that I am not doing correctly, as I can measure some and not others. Thanks in advance.

 

Anthony

[Zerosquare]

Hey, you almost found the solution yourself

 

Measuring AC with a multimeter set to DC (which I assume is what you're doing) will indeed result in a zero volts reading. Depending on the multimeter you're using, there should either a switch position marked V(olts) AC (sometimes this is the drawing of a sine wave), or a button to press to select AC mode, which will give you proper readings.

Edited April 16, 2006 by Zerosquare

[acharris]

Hi and thanks for the reply. Using the AC setting did work on the SNES adapter, but give no reading on the game gear one so I think it is dead.

 

The thing with puzzles me is that how come my universal adaptors will give me the correct reading when the meter is set to DC, but the Snes and sega ones will only give me a reading in AC, yet the Atari 2600 adapter on AC, it gives me 18v, and on DC it reads nothing, yet the adapter is only rated 9v, and this is on two meters.

 

Thanks in advance.

Anthony

[Zerosquare]

You're welcome

 

A few clarifications :

 

- An AC adapter, when measured in DC, will usually read zero (or a very small voltage).

- A DC adapter, when measured in AC, may read zero or any value, usually different from the DC one ; it depends on the meter (for the technically minded : whether it uses AC coupling, True RMS, etc.)

- Those adapters have usually no real regulation ; the voltage written on them is the one they put out approximately when connected to a load drawing the current they're rated for (e.g. 800 mA) ; without a load (such as when you're measuring them with a meter), the voltage may be 20% higher, or more.

[acharris]

Thanks for that clarification, I understand now. I am slowly learning electronics in my own time using books and stuff, so basic stuff like that I am not fully aware off.

 

Thanks again for the explanation, some other knowledge I learnt now.

 

Anthony

[A.J. Franzman]

BTW, if that 2600 adapter turns out to be bad, it may be repairable. There are only about 4 ways that they go bad, approximately in order of most to least common:

A) The wires break inside the cord (usually where they come out of the cube)

B) The capacitor dries out and goes down in value or open (or it shorts out, explodes and becomes open )

C) One of the transformer windings goes open (usually the primary)

D) A diode shorts or goes open

 

ALL of these faults can be fixed (though for C it's usually not worth it unless you can find a proper bare transformer to replace the one in the cube).

 

In recent months, I have fixed several instances of A, one of B and one of C (I did happen to have one appropriate replacement transformer on hand). Bad wiring is easiest to diagnose and fix.

Edited April 18, 2006 by A.J. Franzman