ICL System 25 restoration during 2012

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Each TNMOC project has either a working group or project team assigned to do the work. Working groups are either managed in association with the CCS (Computer Conservation Society) or solely within the Museum.

The latest updates on the ICL System 25 restoration project by Johan Iversen and Delwyn Holroyd during 2012.

Previous years' updates: 2011, 2010.

19/05/2012 update from Johan Iversen

A few weeks ago, the power supply in the System 25 started playing up and has now failed. With the PSU in the other system also faulty it means we don't have a working System 25 at the moment. Both supplies have been moved to the workshop. On one unit the fault appears to be with the -12V, falling to -10.6V, causing the logic unit to disconnect the power rails from the computer. The unit has now been inspected and adjusted by Phil and the Power Supply is now under soak test. The other power supply is still under investigation. The PSU failures are unfortunate as the demo program had just been enhanced before the System 25 threw its teddy in the corner.

The new fans arrived and have been replaced in the System 25+, however after inspection it was decided not to change them in the other System 25.

Also a few weeks ago a desktop version of the System 25 was discovered in our storage block, along with its dual hard disk units. It has been cleaned up a bit and initial internal inspection indicates that there might be a good chance of getting it powered up and running. Gallery Image 2 shows an ICL archive image of the computer.

All the System Ten instructions have now been implemented in the Semulator along with the facility to single step instructions.

Last week we also had small donation from John the ex Europa Sports System 25+ support engineer of some spare boards for the System 25+, a System Ten 20M disc pack, model 42 (System Ten) disc drive circuit diagrams, some manuals and a 20K (20,000 x 6 bit) store board which is on display.


24/03/2012 update from Johan Iversen

The Semulator is progressing well, just one original System Ten instruction to implement and it can now read/write virtual tapes. Some bad news, the power supply in the System 25 Plus stopped working, so as a stop gap the PSU from the Europa Sports System 25 (as it has no fans at the moment) has been used.


03/03/2012 update from Johan Iversen

Now that the bootstrap program load utility is complete I can now concentrate on developing some demo programs for the system. The first one is now complete and replaces the simple, naff Hello World program. This new demo, see Gallery Image 3, displays with some simple text animation the old ICL logo and some System 25 information, it well be developed further over the coming weeks.

The System 25 is still occasionally scrunching tapes, but I think this is due in part to the tape not being firmly pushed into the drive. Since, I have been making sure that the tape is firmly seat the occurrences of damaged tapes has dropped (famous last words).

Also in development is a System 25 Semulator (a mix of Simulator and Emulator, as I cant quite make up my mind which of the two it really is). Which is progressing well, nearly all the original System Ten instructions have been implemented and hopefully a basic version will be able in a few months time. One of the problems with its development is the limit amount of information available. So some of my time is spent testing instructions, etc., to see what results they give so it can then be implemented correctly in the semulator. Still this does increase the understanding of how the system works (which cant be a bad thing).


18/02/2012 update from Johan Iversen

Finally got the bootstrap program to work. In a nut shell it was trampling over the program to be saved when being loaded. The bootstrap block size was too big, a miscalculation by me! Gallery Image 4.


04/02/2012 update from Johan Iversen

The power supply repaired by Phil has been re-fitted into the System 25 system, which was then powered up successfully, however the system could not be left on for very long as the cooling fans still need replacing. The System 25 Plus gave a us a scare, while using it, the system indicator lights that where off started to glow dimly and when accessing the CMT the system would hang. The problem was found to be that the 5 volt supply had drifted out of spec. After re-adjustment every thing seem to be fine again. Development of the Bootstrap program is ongoing, still getting data corruption when reading the tape. Some more good news on the documentation side, the engineer who supported the System 25 plus from Europa Sports has scanned his engineering manuals and sent me the scans.

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