IBM 5100 (Power Supply)


Power Supply Replacement

This page is a summary of information as originally discussed here.

Removing the IBM 5100/5110 PSU is just a few screws, but also unplugging the AC lines, a couple ground wires, and detaching from the external I/O box (which also passes power to the external devices). Here is what the stock PSU looks like:

I happened to acquire an IBM 5110 Type 2 that had no power supply. I verified that all the internal cards still worked, by placing them over into my other IBM 5110 that does have a power supply. I was then motivated to try and find a substitute for the IBM 5110 power supply. But there is no off-the-shelf option. So, I pondered ways to construct my own power supply.

Below is what I came up with (which is three parts plus wiring), as compared next to an original IBM 5110 PSU for reference:


Here is the set of parts used:

Additional background:

The internal PSU is essentially the same between the 5100 and 5110: it does AC to DC conversion, converting 115VAC to +12V, -12V, +8.5V, +5.0V, -5.0V. The PSU in the 5120 may be different since it has a larger screen and disk drives.

From the System Logic Manual, the “DC” side of the power supply has metal connectors arranged as follows (not every side of the connectors is used):

The markings in YELLOW in the above are my own personal annotation. Independent of however the AC/DC conversion is performed, ultimately the task of this power supply is to provide the set of DC outputs. As long as you have the original wiring harness of the power supply (or mark the wires when removing an original power supply that no longer works), then making a new PSU is fairly straightforward.

Another Option

Without using the MeansWell AC/DC converter, here is what my actual first approach was for how the IBM 5110 PSU could be substituted with modern components:

Using a VAC/VDC “power brick” converter that is typically included with a modern laptop (just about any since 1990 will do — but look for 15VDC or greater and 4A or greater output). Just splice the VAC side to the black/white AC power lines in the 5110, then distribute the VDC side to a set of “step down” converters. These “step down” buck converters take the output of the power brick (19VDC in the example above) and regulate it down to what you need: 12V, 8.5V, 5V. As for the negative voltages, you can’t just invert the negative and positive wires. However, I came across an article that describes how to wire up these same buck-converters to do inverted (negative) voltage outputs.

Then the only difficulty is creating your own wiring harness, to connect these inverters to the power wiring harness of the stock IBM 5100’s. Below is what this setup looks like:

It is compact enough to still fit within the IBM 5100/5110 PSU bay, but just barely (after also including the “power brick” AC/DC adapter).

Example of “boost buck converters” used:

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