{"id":10429,"date":"2023-04-13T17:57:37","date_gmt":"2023-04-13T15:57:37","guid":{"rendered":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/?p=10429"},"modified":"2023-04-13T17:57:37","modified_gmt":"2023-04-13T15:57:37","slug":"kenbak-1-replica-project","status":"publish","type":"post","link":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/2023\/04\/13\/kenbak-1-replica-project\/","title":{"rendered":"Kenbak-1 replica project."},"content":{"rendered":"

Background<\/strong><\/p>\n

The KENBAK-1 was developed by John Blankenbaker (and was named after him) in the early 1970s as a teaching tool. Its design guidelines were that it had to be low-cost, educational and able to satisfy the users with simple programs. It could be a serial computer, hence a slow one, which would have reduced the costs and yet meet the such requirements. It would have to handle as many programming concepts as possible. Due to its small size, its native language would have been the machine language. Above all, it had to be a stored-program computer (Von Neumann machine). The aim was to design a simple computer.<\/p>\n

Designed before microprocessors were available, its logic consisted of 132 standard TTL integrated circuits mounted on a single PCB. The serial memory was implemented using 2 MOS shift registers of 1024 bits each, for a total of 2048 bits. Input was accomplished via switches and output was displayed via LEDs. Although the computer had a clock of 1 MHz, it processed only a few hundred instructions per second, because it had a serial architecture, so it processed only one bit at a time.<\/p>\n

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Sales began in 1971 at $750 for an unit fully assembled and working. Expert users were enthusiastic about it, but it was very difficult to convince beginners that they could buy a real computer at that price. The first (and only) production run by the Kenbak Corp. was of 50 units with serial numbers starting at 167.
\nProduction machines differed slightly from the prototype in style, but had the same instruction set and performance. In 1987, among several historical computer candidates, the Kenbak-1 was elected by the Boston Computer Museum as the first commercially available \u201cpersonal computer\u201d (PC).
\nYears ago a replica was sold, on\u00a0a website (http:\/\/www.kenbakkit.com\/<\/a>) that is no longer updated, but reports some diagrams and component lists. Further photos, information and material can be found on various other sites.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

Critical issues
\n<\/strong>\u2022 The PCB has to be made starting from photos: high-resolution ones are available but with components mounted, those without components are low-resolution ones. We will try to overlap them to get the complete traces.
\n\u2022 There is one component (1404a) quite rare, and 4-5 others of medium rarity.
\n\u2022 Case dimensions have to be deduced from indirect information, such as photos and proportions compared to other objects whose real dimensions are known.
\n\u2022 The need to reproduce the mechanics.<\/p>\n

Realization
\n<\/strong>The realization of the printed circuit board was made possible thanks to the patient work carried out by Stefano Ferilli (printed circuit design) and Gianfranco Mazzarello (production of the gerber file essential for the board production). Subsequently, the team composed of the manager, Michele Perniola, and Stefano himself, moved on to the realization of the prototype. The realization of the front panel was made possible thanks to the electrical components and the metal hexagon made available by Stefano. The realization of the case was made possible thanks to the commitment and competence of Vito Fariello.<\/p>\n

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Michele Perniola, the Project Manager<\/figcaption><\/figure>\n

Here are some photos that show the work done.<\/p>\n\n\n\n

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Beginning of the inspection with a microscope<\/figcaption><\/figure>\n\n
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Even the 3D printed keys are ready<\/figcaption><\/figure>\n
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On 30.11.2021 the prototype of the front panel was made.<\/figcaption><\/figure>\n
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On 23.12.2021, thanks to Vito Fariello, the prototype of the case arrives at the headquarters.<\/figcaption><\/figure>\n

December 30, 2021 update<\/strong><\/em><\/p>\n

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Here is the result of the assembly. There are only 4 ICs to go.<\/figcaption><\/figure>\n

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January 15, 2022 update<\/strong><\/em><\/p>\n\n\n

January 24, 2022 update<\/strong><\/em><\/p>\n

Paper labels were attached with transparent Magic tape. It is a temporary solution we can remove without causing any damage to the panel.<\/p>\n\n

The key caps made by Vito Fariello were fitted.<\/p>\n\n

January 31, 2022 update<\/strong><\/em><\/p>\n

Front panel wiring.<\/p>\n\n\n

April 13, 2022 update<\/strong><\/em><\/p>\n

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First power up.<\/figcaption><\/figure>\n\n\n

Short circuit hunt on the printed circuit board.<\/p>\n\n

… there is no short circuit. Unfortunately, SN74LS54 ICs have been supplied instead of SN7454. This is one of the few cases where the ’74LS’ series IC is not a valid substitute for the corresponding ’74’ series, as they have a completely different pinout\u00a0😖.\u00a0We had to order correct ICs:\u00a0 they should arrive in the next few days.<\/p>\n

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Manual and diagrams ready for debugging<\/p>\n\n

April 20, 2022 update<\/strong><\/em><\/p>\n

“Memories” (shift registers 1024 bit SY1404A) have been installed.<\/p>\n\n

An error has been identified on the printed circuit board under the IC 104. The socket has been removed, the track has been cut and a new jumper has been installed (next to the one previously made to replace the missing track).<\/p>\n\n

April 24, 2022 update<\/strong><\/em><\/p>\n

Unfortunately, the very difficult acquisition of the printed circuit design “didn’t come out well”, especially on the component side, where the only good photo available was…with the components soldered.
\nAbout 16 errors were identified considering both missing and incorrectly connected tracks.<\/p>\n

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The tracks have been temporarily “fixed”. Some fixes were done by unsoldering sockets to cut bad tracks underneath them.<\/p>\n

The behavior of the lights\/buttons now feels “more natural”.<\/p>\n

The next step will be the check of the test patterns reported in the Kenbak manual.<\/p>\n<\/div>\n

May 26, 2022 update<\/strong><\/em><\/p>\n

The Kenbak-1 prototype is finally functional. It has been tested with an appropriate program included in the manual, which results in the scrolling of the indicator lights.<\/p>\n

https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-content\/uploads\/2021\/09\/ee5cae02-fa6b-44f9-8ebd-ab8b54da617c.mp4<\/a><\/video><\/div>\n

June 2, 2022 update<\/strong><\/em><\/p>\n

We move on to painting the case.<\/p>\n\n

Stages of assembly.<\/p>\n\n

The adhesive printed panel arrived.<\/p>\n

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Final stages of the assembly…<\/p>\n\n

Video of the test of the completed prototype behaviour.<\/p>\n

https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-content\/uploads\/2021\/09\/7386eb16-f099-4b1a-9eae-203fd3692584.mp4<\/a><\/video><\/div>\n

Photo of the assembled prototype.<\/p>\n

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Background The KENBAK-1 was developed by John Blankenbaker (and was named after him) in the early 1970s as a teaching tool. Its design guidelines were that it had to be low-cost, educational and able to satisfy the users with simple programs. It could be a serial computer, hence a slow one, which would have reduced…<\/p>\n","protected":false},"author":1,"featured_media":9372,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[126],"tags":[390,40],"class_list":["post-10429","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-laboratorio","tag-kenbak-1","tag-retrocomputing"],"_links":{"self":[{"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/posts\/10429","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/comments?post=10429"}],"version-history":[{"count":0,"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/posts\/10429\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/media?parent=10429"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/categories?post=10429"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.apuliaretrocomputing.it\/wordpress\/wp-json\/wp\/v2\/tags?post=10429"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}