DEC PC05 - Failures

Parent Category: Stories Category: Love affair with the DEC paper tape PC05 Written by Administrator

Repair sessions

From May to July 2015, I repaired those six PC05 (and cannibalized an incomplete 7th one). I stopped any other RetroComputing activity, since working in an assembly-line manner is highly efficient. When repairing, most time is spent in understanding the machine under your finger tips and becoming familiar with the documentation, this part has only to be done once for all PC05's together.

pc05 under test

 On the backside, it was very boring at the end. And often I felt like in a private little hell, where a handfull of problems reappeared in a seemingly endless loop.

Standard procedures

 For each PC05, I performed these steps:

pc05 faston tabs


A special Flip-Chip extender.

For debugging and repairing, I needed to operate some electronic modules outside the card cage. I build a special flexible flip chip extender from an flip chip backplane socket.

flipchip extender flexible

DEC Field Service had no need for such a tool: they did not repair, but just located the bad modules and replaced them.

pc05 module on extender

After having used that extender the first time, I could not imagine how I ever could work without it!


The Big Failure List

This is the list of all failures I found and fixed. Interestingly, every device had several severe errors. Since a PC05 surely was taken out of service on the first unrepaired failure, follow-on damages must be attributed to the conditions in the warehouse where they were stored for years.

PC05 #1

PC05 #2

This PC05 had almost all possible failures. It could have been used in a Field Service school for training purposes!


PC05 #3

 pc05 triac

PC05 #4


PC05 #5

Here reader data bit #2 had intermittent failures, caused by three different sources: amplifier threshold, lamp brightness and a defective data latch! This took a while to recognize ...


PC05 #6


AND FINALLY: The PC05 of my computer club

pc05 defective modules


All these PC05's pass XXDP diagnostic "ZPCA" now!

xxdp zpca prg2