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Old 05-26-2007, 03:19 AM
phe phe is offline
Join Date: Dec 2006
Posts: 48
Default Power questions

I'm down to the final step, but I want to check my assumptions before I wire up the power supplies.

I'm planning to connect the black wire from the power cord to one of the "AC SW" terminals on the D/C board. Then I'll run a red wire from the other "AC SW" terminal to the L terminal on one power supply and then further on to the L terminal on the other power supply. I'll connect the white wire from the power coard to the N terminal on one power supply and then further on to the N terminal on the other power supply.

Is this correct?

Next questions:

The large power supply V+ terminal is +8vDC
The small power supply V+ terminal is +16vDC
The small power supply V- terminal is -16vDC

PAge 72 of the MITS manual says pins 1/51 are +5V, pin 2 is +15V, and pin 52 is -15V. I assume we are to use +8V, +16V, and -16V, correct?
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Old 05-26-2007, 10:54 PM
Grant Stockly Grant Stockly is offline
Join Date: Jan 2005
Posts: 447

Until you "trim" the power supplies they will be 7.5vDC and +/- 15vDC. On each power supply there is a pot to adjust the voltage. I found it runs fine on +7.5 and +15/-15. The vintage Altair used a linear power supply that when loaded down will have a dropping output voltage. The switching power supplies drive hard at 7.5v until overloaded.

On some of the vintage units the unloaded voltage of the +8v line was +12v to handle TONS of cards. This causes a problem when someone buys one of these units off of ebay (or any second hand place) and wants to test the system with only a CPU card and memory card. They over heat and go POOF. : )

The switching power supplies eliminate this worry. : )

The MITS manual says things like "+5v" because that is what the voltage will be after regulating... You might find a few different descriptions of the power lines in different places of the manual. Do you have close up pictures of how I wired my power supplies? In the manual?
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