{"id":2619,"date":"2015-08-04T19:06:40","date_gmt":"2015-08-04T17:06:40","guid":{"rendered":"http:\/\/museo.freaknet.org\/?p=2619"},"modified":"2025-08-29T15:40:37","modified_gmt":"2025-08-29T13:40:37","slug":"restauro-pdp1123plus","status":"publish","type":"post","link":"https:\/\/museo.freaknet.org\/en\/restauro-pdp1123plus\/","title":{"rendered":"PDP11\/23PLUS restoration"},"content":{"rendered":"

We saved this PDP11\/23PLUS some years ago in Pescara, thanks to Alexander “Smilzo” Gnoli. It was an incredible trip with a camper, with Giuliano “Vampire”. We filled a lot of hardware inside our Fiat 242 camper, and eventually stored everything in our deposit.<\/p>\n

First analysis revealed the main problem: power supply was searched for parts \/ missing. This power supply was necessary also to generate a particular 60Hz clock needed for some operating systems. We searched for\u00a0some time and stored the computer again.<\/p>\n

Two years ago, with Andrea “mancausoft” we considered the idea of adapting a common ATX pc power supply, creating a circuit for the 60Hz clock. We were thinking about creating it from our 220V power line (at 50Hz), but we were in a hurry and had to store the computer again.<\/p>\n

One year ago, we built a prototype adapter to connect the ATX PSU to our PDP11\/23PLUS, with a programmed ATtiny85 to generate the needed clock (a particular choice: instead of creating it from 220V, we decided to use the ATtiny85). Test was succesful, but the system was stuck on boot. We were out of time to do a complete debug so we had to store the computer again.<\/p>\n

Recently Andrea made the final adapter board, the one that you see in the following pictures. We finally tested and mounted everything; system power on correctly, memory test is ok, but we receive an error on the RL02 boot unit.<\/p>\n

So we decided to open the card cage and check every connection, jumper and board inside. CPU is a\u00a0KDF11BA (manual is\u00a0\u00a0here<\/a>). We also made a ROM backup. We extracted the RL02 drive board, cleaned contacts with pencil eraser and WD40, rebuilt the system again… and we had a normal boot! System is now in 100% working order \ud83d\ude42<\/p>\n

Phase one, first experimental board:<\/p>\n