Tag Archives: computers DEC pdp retro

Consolidated Computer Inc. PDP-8 Clone – Part 4 2nd PSU refurbishment.

The second PSU is the same model as the first and I went about its refurbishment in the same way.

Firstly, I removed the capacitors. Here was the first problem. One of the smaller capacitors was leaking. Straight over to RS components to see if I could find a replacement. Bingo, next day delivery! Amazingly I found a capacitor of the same diameter with the screw terminals on the same centres with the same screw thread. Marvellous.

The faulty capacitor from the second CCI power supply. The new capacitor is on the right.

I tested the other caps with my capacitance meter and they all looked feasible. I then brought the up, one by one on my bench suply with the current fixed at < 20ma. As each one stabilised at it correct working voltage, I noted the leakage current and this was typically around 0.6-0.8ma. That’s not bad at all for 40 year old caps.

Next the whole unit got a good dust, the terminals and fuses were cleaned with a wire brush and everything was reassembled prior to testing.

The second CCI power supply after refurbishment. The new capacitor is on the left.

On of the wires running from a rectifyer was showing signes of bad corrosion so I made a new cable up with new connectors and fitted that.

I went through the same tests with car tail-light bulbs as I had for PSU1 and they lit up beautifully.

Two down, one to go.