7800 Voltage Tolerance

[Inferon]

How many volts are too many to feed the 7800?

I've wanted a 7800 for quite some time. I was lucky enough to be able to pick one up on a recent road trip. When I got home I tested the 7800's stock power supply and found that it was feeding the 7800 13.4V instead of the recommended 9V. Is this too high for the 7800, or is it just fine?

 

Thanks for your time!

[Rybags]

From what I gather, 7800 only uses the 9V for part of the video generation (colour?), remainder of the system uses regulated 5 Volts.

 

The problem you might encounter is that too much over 9V could kill the voltage regulator. But it can be a regular thing that power supplies will read more voltage than they're rated when not under load, though not usually more than 10%

[Inferon]

Great! Acording to another AA post (http://atariage.com/forums/topic/74388-7800-voltage-regulator/) the 7800 uses the TI UA7805C. Acording to it's spec sheet it has a maximum Vin rating of 25V. So it looks like I should be fine. Thanks for the help!

[7800fan]

If you checked the power supply when it's not connected to 7800 or with 7800 on, your reading may end up high. Power supply brick with no load tended to read much higher. When it's connected to a load (a 7800 that is turned on for example), it should be closer to 9v.

 

Your power supply's fine.

[+Stephen Moss]

7800fan is correct, those types of power supply are created cheaply with the minimum number of components and use a crude method of voltage regulator based on losses in an underrated transformer, hence the higher off load reading.

 

Inside the 7800 is a 7850 voltage regulator that drops the input voltage down to a regulated 5 volts DC, this will operate correctly from a typical input voltage range from 8 to 30 volts DC, although more volts = more power dissipation running the risk of it going into thermal shutdown so generally the closer its input voltage is to 9 volts the better.