Power Supply Pin Voltages & Polarities

[Convergent MightyFrame]

Hello, all.

I am reconstructing my first 7300, and I am missing a power supply. If any of you know the correct pin voltages and polarities, I believe that I can take any of my modern power supplies, and configure it properly.

Here's a picture for reference, where I arbitrarily number the pins from 1 to 18

http://6reoquestions.com/misc/ATT_UNIX-PC_7300_pwr-suppl-pins.jpg

Thanks!
-AJ

[DoN. Nichols]

O.K. I can't be sure whether your numbering is backwards from
what I have or not -- but it will be easy enough to check.

First off -- all *odd* pins are ground (1 through 17).

Look for a power connector for either the floppy drive or the
hard drive. Of the four pins, the middle two are always ground (and
should be black). (5V is normaly red, and 12V is normally yellow, for
double checking the rest of what I will be typing in. This is from
sheet 1 of 25 from the schematics section of the _Technical Reference
Manual_. There are actually two preceding pages of schematics (1 and 2
of 2 for the DMA address logic).

Pins 12, 14 and 16 are the +12V pins.

Pins 2, 4, 6, 8 and 10 are the +5V pins.

Pin 18 is the -12V pin -- used only for the serial ports I believe.

Remember to double-check the grounds being tied to the odd pins.
If they are connected to the even pins, your numbering is backwards from
that in my schematics. (I would think that pin 1 should be brown, two
should be red and so forth, as in the resistor color codes, so what you
have labeled as pin 18 in your photo is likely really pin 1.

There are three sets of the schematic pages -- for three
different versions of the system board.

I would strongly advise you to connect the hard drive directly
to one of the PC connectors for 12V and 5V, as the current consumed by
some hard drives tends to burn that 18-pin connector over time -- and
later power suplies for the 3B1 version had a cable running directly
from the power supply to the drive.

Good Luck,
DoN.

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[Convergent MightyFrame]

DoN...thank you again! You are always a wealth of information.

I tested with a VOM, and sure enough, my arbitrary numbering in my diagram is exactly backwards. Just as you say, pin 1 is brown, 2 is red, etc.

I will connect it like this to my power supply, and let you know here what the results are.

Thanks also for suggesting the alternative power connector for the hard drive. I will follow that advice.

Keeping my fingers crossed...

Thanks always,
-AJ