These pages document in as much detail as possible my experiences and results of repairing and restoring a HP-85A and HP-85B desktop computers.

I started on this project in June 2019 with no experience at all with these computers, and having never used one, I was only vaguely aware of their history and capabilities. I had often seen reference to these computers in the service manuals for HP test equipment, that relied on an HP-85 as the programmable controller for HP-IB needed for test and calibration procedures.

Much of my exploration was guided by the many other people who have also maintained these computers, and have thankfully documented their experience in online groups/forums, personal web sites, and YouTube videos. My contribution will be a mix of the web site you are now reading, and a new add-on board EBTKS for the Series 80 computers, and some Youtube videos that this site links to.

The techniques that I describe in these pages are a combination of

  • Techniques that other people have used

  • Modifications by me to these techniques

  • Techniques that I have developed that appear to be original to me.

As I have had many years of experience with this type of work, I have developed preferences for specific Tools and Materials and I have documented the relevant ones here as well.

Projects like this have both successes and failures. I have documented many of my failures as well as successes. Have you ever noticed that when you are looking for a lost item, and you find it (eventually), it is found in the last place you looked. For some of the repairs I have done, I stopped trying new techniques once I had success. For some, I kept trying new things in an endeavour to find better solutions. My repair of the Keyboard Plungers and the Tape Drive Capstan fall into this category.

I have been successful with the following repairs:

  • Repair the tape drive capstan

  • Upgrade the tape drive capstan to work with DC2000 and DC2120XL tapes

  • Repaired NOS DC100 tapes (making tiny holes for the BOT sequence)

  • Repaired HiTek keyboard plungers

  • Converted incompatible Stackpole plungers (Green) to work in the HP-85 Keyboards

  • Manufactured replacement flat flex cables including service cables

  • Manufactured a replacement for the plastic optical servo disk for the tape drive

  • Researched the signals in the tape drive under many operating conditions

  • Collaborated with Russell Bull and Everett Kaser in designing a reliable replacement for the tape drive: EBTKS