Step 2: Reviving the +5V PSU

Parent Category: Stories Category: VAX 11/750: The Resurrection of a Comet Written by UlliH

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How one can deal with old power supplies

There are two ways to deal with old power supplies in general:

I did it the "quick and dirty" way with my VAX-11/725 (I was lucky - the only fault was a short in the line-in filter), but I didn't want to tempt fate again this time with the VAX-11/750.

So I studied the 7104's schematics and "Power System Technical Description" to learn about the way it works.

I used the following print sets and manuals:

both_psus_still_in_place_small

Both PSUs (+2.5V left, +5V right) still in place and uncleaned.

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This is the +5V PSU (DEC # H7104-D) opened. On the left two "hand grenades" (about the size and about the impact when exploding).

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Both boards (5V Bias/Control and +/-15V Regulator) removed; left side: Output Assy - down right : Bottom Panel Assy

The H7104 PSUs are of a modular design. This is very advantageous because you can test different assemblies separately and one after another.



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