Monday, October 5, 2009

Building the Power Supply

Note that the 4 pin header looks a little rough, because it's actually a cut down version of the 6 pin header. If I took crapier pictures you wouldn't notice :D.

Today I pulled out the 2 Stancor transformers and put together the power supply. I didn't have all of the parts. After spending too much money on hard-to-find chips and carbon composite resistors, I decided it was time to do what we all should do, a little spring cleaning!
So I dug through the basement and garage and found a decent 2 prong power cord, and a fuse housing wire (from an old Panasonic car stereo equalizer) . There were also 4 nice nuts and bolts probably for mounting the stereo equalizer that I snatched out of the equalizer box to use for mounting the (2) Stancor transformers. While digging around I also found a brand new 125v ON -OFF toggle switch that was perfect for this project, in one of my parts bins down in the basement. I grabbed a handful of various old male/female wire connectors I thought I'd find useful as well.

I first started with assembling the 6 pin Molex connector housing and pins. I soldered each connector pin to each of the corresponding Stancor transformer wires after crimping them. I added wire connectors between the fuse wires and also for the ON/OFF switch. Every minute or so I referred back to the Apple 1 manual I had displayed on my computer screen just to make double sure I wasn't screwing up. I had never built a power supply before, so I was a little worried I was either going to hurt myself or fry the board. I took my time, and everything came together just fine. I powered up the board (after soldering the 6 Pin and 4 Pin headers to the board) with the supply and checked a few points to make sure I had the expected voltages (-5, +5, -12, +12). I did this using 3 tools:

1) Oscilloscope
2) Logic Probe and
3) Multimeter set to measure DC voltage

Everything looked OK to me except for one area, which I am still confused over....
The Apple 1 schematic (drawing 101 - Power Supply) shows J3 pins X, Y, and Z where X = GND, Y = +12v and Z = -12v. I measured 22.5v and -22.5v for both of these points. However, the manual said that these 2 pins should not be used, and if they are used need to be regulated (the voltage is not regulated as is).

After cleaning up a bit, I went ahead and soldered the jumper points above the 74154. I used a combination of the Apple 1 manual - schematic notes, and the scant instructions (from the web) from Obtronix. They are slightly different, but I don't know why:

Apple 1 Manual (schematic notes) jumper connections:
Y => CSF
Z => CSD
W => CS1
X => CS0 (zero)

Y => F
Z => D
W => E (Note Apple jumps W=>CS1)
X => 0 (zero)
R => C

I took a look at a few Apple 1 images, and found a couple with jumper wire from W=>E so that is what I went with as well.

I powered up the board again and checked a few more points. I shut everything down, cleaned up a bit more, then proceeded to install the chips. After installing all of the chips, I powered up the board again looking for smoke, arcing, fire, flames, explosions, and nothing happened. But this time the board started producing heat. The 74154, the ROMs and the LM323k were all generating heat. The 6502 was not, however. I checked the voltages for 5v on the 6502 and everything looked fine.

So, enjoy the photos, and tomorrow after work maybe I'll see if I can knock out the keyboard and video.

1 comment:

  1. J3 Y +12V and Z -12V are unregulated but rectified and smoothed outputs from the P-8667 transformer. They are the same as the inputs to the LM340-12 and LM320 MP-12 voltage regulators. I'm guessing that Woz thought that these regulators couldn't support the additional current draw from expansion cards, so he simply connected the unregulated inputs to the expansion slot. I believe that the voltages you are measuring here are expected.