Atari power supply half voltage???? AR-II

Steverd

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After testing the AR-II board on my Battlezone all test points show about 1/2 of what they should in AC and DC.

So then I tested a few points on the Atari power supply and I am also getting about 1/2 of what the readout should be.
F4 and F5 read 18vac instead of 36
F6 was correct at 6.1

I tested the pins on J5 and they are off also.

What would cause this low voltage? The bridge or C1?
I know the transformers are rarely the problem.
The power cord looks good and I am getting 122vac

Thanks
 
You do not have a problem. The readings are fine.

This is due to a common mis-understanding of voltage measurement. These AC voltages should be made, of course, with the meter is AC volts mode. AND they also should be made NOT relative to DC ground, but instead relative to the "other leg" of the AC voltage.

This is part of the reason why the fuse block is not the best place to make these measurments. Instead, make them on the output jack (J5) as follows:
- Between pins 8 & 9 (that means red lead on one, black on the other--doesn't matter which for AC) you should have about 6VAC.
- Between pins 6 & 7 you'll find your 36VAC. Note that the latter is "center tapped" which means that it is held relative to DC GND, which is why you measure about 18V between one (or each) of the legs to GND.
 
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