Isolation Transformer Voltage Question

I have a project I've posted questions on before - my Frogger converted
into a Cal Fifty. I've got my cracked neck board repaired (I
think/hope) for the WG 4600 monitor and I'm nearing being able to test
it. I want to make sure I'm getting the right voltage (120V) to the
monitor.

My question: is there a secret to measuring the voltage coming out of
an isolation transformer?

I'm trying to test the voltages on the two secondary lines coming out
of the transformer that go to the monitor and I'm getting some strange
values.

I'm using the tranformer from the original Frogger power supply. On the
primary side, the 1 and 3 connectors are hooked to 120VAC. When I test
the two (secondary) lines coming out of the transformer that go to the
monitor, I get 18V on one and 25V on the other. When I swap my leads
connected to the primary inputs, I get 39V on one 10V on the other. The
tranformer is connected to Earth ground and my meter is set to test AC
voltage. Shouldn't I get somewhere around 120V on one of the lines?

I have a new transformer I got from Bob Roberts. I tried the same setup
and test with it and got 38V and 136V. When I swap the connections to
the primary, I get 122V and 219V.

You need to check between the two output leads on the transformer for
the 120V, it shouldn't read anything from earth ground to the
secondary, ( that's why it is called an isolation transformer, it
isolates the secondary form the input power ), the odd voltages you
read are stray noise that your meter picks up.
Dick

Brandon wrote:
> I have a project I've posted questions on before - my Frogger converted
> into a Cal Fifty. I've got my cracked neck board repaired (I
> think/hope) for the WG 4600 monitor and I'm nearing being able to test
> it. I want to make sure I'm getting the right voltage (120V) to the
> monitor.
>
> My question: is there a secret to measuring the voltage coming out of
> an isolation transformer?
>
> I'm trying to test the voltages on the two secondary lines coming out
> of the transformer that go to the monitor and I'm getting some strange
> values.
>
> I'm using the tranformer from the original Frogger power supply. On the
> primary side, the 1 and 3 connectors are hooked to 120VAC. When I test
> the two (secondary) lines coming out of the transformer that go to the
> monitor, I get 18V on one and 25V on the other. When I swap my leads
> connected to the primary inputs, I get 39V on one 10V on the other. The
> tranformer is connected to Earth ground and my meter is set to test AC
> voltage. Shouldn't I get somewhere around 120V on one of the lines?
>
> I have a new transformer I got from Bob Roberts. I tried the same setup
> and test with it and got 38V and 136V. When I swap the connections to
> the primary, I get 122V and 219V.