The University of Iowa's DEC PDP-8

Restoration Project Rules

Part of the UI-8 pages
by Douglas W. Jones
THE UNIVERSITY OF IOWA Department of Computer Science



Personal Safety

There is heavy equipment in the lab, and some of the materials we will work with pose hazards. Therefore:

Mechanical Safety

The rack holding the computer weighs 225 pounds. The computer itself (including the power supply) weighs 250 pounds. When the computer is extended from the rack to the limit of its rack slides, it is dangerously close to being unbalanced. The risk is greatest when the weight of the rack is carried on the wheeled casters and the casters are pivoted toward the rear. Therefore:

All of the rack-mounted equipment can be removed from the relay racks, but some of it is heavy, fragile or both. Furthermore, careless work poses risks not only to the piece of equipment being mounted or dismounted, but to the adjacent equipment. Therefore:

Electrical Safety

This computer contains power supplies with outputs of up to 40 volts, and the majority of the logic operates between a +10 volt bus and a -15 volt bus. These are hazardous voltages that are significantly higher than the voltages used in modern logic. Furthermore, the 110-volt power on the input side of the power supply is exposed on terminal strips inside the machine. A current of 20 milliamps (0.02 Amps) can kill a person. The capacitors in our computer's main 15 volt power supply store 47.25 Joules (of energy), comparable to the amount of energy in the most powerful air guns, or the energy in a 1 kilogram weight dropped from 4.82 meters, or a 1 pound weight dropped from 34.87 feet.

Chemical Safety

This machine was built using tin-lead solder, and some of the chemicals we will use in cleaning and restoring the machines pose potential hazards.


Circuit boards and power supply wiring on this machine were assembled using tin-lead solder. We will have to connect and disconnect a small number of solder joints during the refurbishment of the power supplies, and it is highly likely that we will have to repair some circuit boards. Lead is toxic and the melting point of tin-lead solder is over 360°F or 180°C, hot enough to cause severe burns. Therefore:


The PDP-8 computer in the retrocomputing lab is one of only a handful of surving rack-mounted PDP-8 systems. We do not know of any surviving PDP-8 systems that include an A-D converter. Beside the value of the system itself, the test instruments and tools we will be using in the lab have value. Therefore:


There is a log book in the lab so that we can track both the status of the project and maintain lab security.

Our goal is to restore things to working condition. If we lose or misplace parts, this will be difficult. Therefore:


The University has long ago cut back on custodial support, and some parts of old computers, most notably the foam used in cabinet gaskets, sheds considerable dust when disturbed. Therefore: