Here is an impression of the pil of 11/34 cards I got.

 

12 M8266 - CPU data path

10 M8265 CPU control

27 CPU programmer console interface

20 DL11  serial communication + clock

6 M??? merory

 

Impressive.

 

I could get them from an DEC service entrprise, which is out of business since long.

When I draw them home, I knew most of these would be defective, because it surely was the "bad selection" of the repair department. I still had the hope that some of these would be still working, and I could build a few working '34s fro these parts.

 

<Foto: alle 11/34 karten auf einem Haufen>

Lottery chances

But while working with these cards, I hadn't  much success: I fast got totally confused, which cards worked with which other ones.

First problem: For build a running system, you need one good card of every kind

<foro> 11/34 cage>

 

If you have too much defective cards, finding a working combination is like a hit in a lottery.

Example: say you need at least memory + serial + bootloader terminator + CPU control + CPU data path + programmer conmsole.: six cards.

If every card has an 80% chance of beeing OK, the chance to build a working system by random picks is
       0.86 = 0,26 = 26%

If every card has only a 50:50 chance of beeing OK, then a chance for a working system is
      0.56 = 0,015 = 1.5%

Luckily I could borrow same "good cards" from a friend  to set a starting point.

So after a filterung run I had abouzt 5 working cards of every kind ... good enough (as I tought).

MTBF

2nd Problem: Even If I had picked "good" cards and got an working 11/34 together, my success would last for long: MTBF (mean time between failure) was horrible low. In the beginning every 5 to 10 run time hours my machine crashed.

And each time I had to go through the procedure of replacing all cards from the dead 11/34 with my pile of "good" cards, until I find the culprit.

In the beginning I was happy that I had so many good cards to change in.

But as the years went by, my pile of good cards got smaller and smaller. Finally, with beginning of 2014, I had only one good CPU and only one RL11 disk controller!

Beginning to repair

It was time to face reality:

I had to learn to repair those cards. And to repair fast in a professional style.

These pages are about what I did then.