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Old 06-05-2008, 11:45 AM
Geoff Harrison Geoff Harrison is offline
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Join Date: Feb 2007
Posts: 104

Originally Posted by Grant Stockly View Post
I wonder if its possible the 7805 was damaged when the power was applied with the bypass resistor and no load?
That's an interesting thought, I've read 7805s don't like to see high voltage on their output side.

I unsoldered the resistor and the regulator is putting out a solid 5v now, but I don't know whether its load handling capacity has been damaged in any way. I may swap it out just to be safe.

MITS used that bypass resistor across the regulator on their 4k board too. I don't know much about circuit design, but doesn't that kind of negate the purpose of a regulator? I assume that when the circuit is loaded normally all the current flows through the regulator, and the resistor comes into play only if a heavy load is added (say, a couple of 16k memory boards), but then what ensures that the voltage stays constant?

I guess when you're testing an unloaded board with this kind of power regulation, it's probably a good idea to put some kind of load on it.

Originally Posted by Grant Stockly View Post
I see you are experimenting with VTL! THAT is amazing code. 768 bytes!
And it runs happily with just 1k of RAM!

I'll put my 16k board in later and try to download basic. It should work, it runs fine on the vintage machine.

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