DEC Computer Power Supply Module Retrofit

In the process of troubleshooting our earliest machines, we had to replace large components called electrolytic capacitors. These are located in all the power supplies for any computer. We successfully replaced these devices and got the machines running. Recently though, we have started to see these devices fail once more. They have a finite life of a maximum of 14 years. That means that we have to replace these devices every 10 to 14 years. Also, the larger capacitors are no longer manufactured, but can still be special ordered. As it is our mission to have our computing hardware last for a lot longer than that, we did our research and engineered a replacement for the power supply modules these capacitors are found in. Our goal was to provide several decades of service without having to service these modules. The photos and descriptions below show the process:

Below is what the original power supply circuit board looked like

When we strip out the circuit board and remove the heat sink, we get this

We created, using a CAD program and a 3D printer, a plastic component mounting for the new components.

As you can see, the plastic mount fit perfectly into the old power module frame.

After populating the mount with all the components it looks like this.

Now we attach the modified heat sink to the original module frame.

Install the assembled component mount in the frame along with the modified heatsink and the new power module is complete.

One of the features of the module is, it has no solder connections, all of them being compression.  Wires are compressed into a square cross section using a stainless steel screw.  This provides very high reliability.

 

The upshot of all this work ( there were 38 modules in various machines ), is power supplies that are more efficient and have a rated MTBF ( mean time before failure ) of 40 years. These power supply modules draw 2/3 less power and produce 2/3 less heat, reducing the heat load on all the components in a machine. In addition, as a result of these changes, the total power savings per year is 250,000 kilowatt hours. Electricity rates in this area of Seattle are about 8 cents/kilowatt hour. That means a direct cost savings on our electric bill of $20,000 a year.