The Short

There is a lurking short within the Calculator.

Since last post, I did very little up until today because I was quite busy.  Today I finished up the hardware and software of the Calculator, and then tried to turn it on.  Recall that last time, the regulator heated up and nothing happened.  This time, the regulator heated up, nothing happened, and there was only 1.6 volts on the bus, not 3.3.  I looked up the datasheet for the 7833 and realized that 4.5 volts was not enough to power it!  I tried it with a 9v battery.  Unfortunately, it didn't work.  I then tried powering it off the VIn of an Arduino board.  I accidentally plugged the 5v output into the Calculator, not the 3.3v output, and the LED backlight of the LCD came on.  Nothing else happened.  When I tried the 3.3v output, it only outputted 1.6 volts.

Next, I put a heatsink on  the regulator, but it didn't work.  Meanwhile, the resistance of the alleged "short" between ground and VCC ranged from 3k ohms to 7.5k ohms.  I am thoroughly stumped.  Tomorrow I will try powering the Calculator off of my ATX power supply.  We shall see whether it requires more than 21 amps (!) tomorrow.

I plan to bring the unfinished Calculator in to school tomorrow.