Atari 800 - 9VAC power supply measuring 11V?

[ElementalChaos]

Hi all, I have a question/concern about the Atari brick power supply I'm using to power my 800.

It obviously is working, but I always check the voltages my power supplies are putting out using a multimeter just to make sure I'm not gonna be frying my system. Measuring the plug without any load, I am getting 11 volts.

Now I don't know if it droops down to a more reasonable level under load or if the 800's power circuitry is able to handle a bit of an overvoltage like that, but is that normal to be getting out of one of these supplies? Should I play it safe and stop using this one? Is there any test point on the 800 power board where I can see the raw voltage after it goes in the machine?

Thank you.

[Kyle22]

It's fine. That is a normal no-load measurement. The regulators can easily handle it.

[+Nezgar]

Looks good to me! Some background:

 

The 7805 regulator requires a minimum of 7V input, and can handle up to 35V (with extra heat generated) for 5V output. So, 11V AC (closer to 9V AC under load) is in a nice place at the lower end of this spectrum.

 

For the 7812 regulator, the 9V input gets doubled to 18, also a nice position between the 14.5V to 30V input requirements for 12V output.

[BillC]

As Kyle22 mentioned there is a difference between loaded and unloaded voltage measurements.

There is also peak versus RMS voltage, most meters give peak voltage measurements.

https://en.wikipedia.org/wiki/Root_mean_square

[tjlazer]

Make sure you don't have the 5200 DC power supply! I made that mistake when trying to power my 1050 disk drive and it was not working correctly!

Edited November 20, 2018 by tjlazer

[shoestring]

Hi all, I have a question/concern about the Atari brick power supply I'm using to power my 800.

It obviously is working, but I always check the voltages my power supplies are putting out using a multimeter just to make sure I'm not gonna be frying my system. Measuring the plug without any load, I am getting 11 volts.

Now I don't know if it droops down to a more reasonable level under load or if the 800's power circuitry is able to handle a bit of an overvoltage like that, but is that normal to be getting out of one of these supplies? Should I play it safe and stop using this one? Is there any test point on the 800 power board where I can see the raw voltage after it goes in the machine?

Thank you.

 

My 1050 is brand new and I can confirm the same readings on the DMM