There are two ways to deal with old power supplies in general:
- Either do a go/no go smoke test (connect it to mains, switch it on and see what happens)
- or do careful systematic tests to assure functionality of separate subassemblies one by one.
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:
- EK-PS750-TD-002 VAX-11/750 H7104 Power System Technical Description
- MP-01022 875 Controller Field Maintenance Print Set
- MP-01021 H7104-D 5 V Power Supply Assembly Field Maintenance Print Set
- MP-01020 H7104-C 2.5 V Power Supply Assembly Field Maintenance Print Set
Both PSUs (+2.5V left, +5V right) still in place and uncleaned.
This is the +5V PSU (DEC # H7104-D) opened. On the left two "hand grenades" (about the size and about the impact when exploding).
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.