website/content/museum/heathkit-zenith-et-3400.md

---
title: HEATHKIT / ZENITH ET-3400
categories:
- Computers
types:
- Home Computer
origins:
- U.S.A.
years:
- '1976'
cpus:
- Motorola 6800 then 6808
params:
  name: ET-3400
  image: /media/museum/photos/heathkit_et3400_system_s1.jpg
  company: /companies/heathkit-zenith
  company_name: HEATHKIT / ZENITH
  specs:
  - label: NAME
    value: ET-3400
  - label: MANUFACTURER
    value: Heathkit / Zenith
  - label: TYPE
    value: Home Computer
  - label: ORIGIN
    value: U.S.A.
  - label: YEAR
    value: '1976'
  - label: BUILT IN LANGUAGE
    value: Monitor in ROM
  - label: KEYBOARD
    value: 17 keys Hexadecimal keypad
  - label: CPU
    value: Motorola 6800 then 6808 (1981) and 6802 (1987)
  - label: SPEED
    value: 1 MHz
  - label: RAM
    value: 256 bytes expandable to 1 KB
  - label: ROM
    value: 1 KB
  - label: TEXT MODES
    value: 6 x 7-segment LEDs
  - label: SIZE / WEIGHT
    value: 30.5 (W) x 30.5 (D) x 10.15 (H) cm. / 2 Kgs
  - label: POWER SUPPLY
    value: External AC adapter
  - label: PERIPHERALS
    value: Prototype area
  - label: PRICE
    value: $199.95 Kit, $279.00 assembled, $99.95 for the ET-3401 course
  tabs:
  - photos
  - emulators
  - links
  photos:
  - title: 'LARGE VIEW #1'
    subtitle: ''
    text: At power on or after a Reset, 'CPU UP' is displayed.
    image: /media/museum/photos/heathkit_et3400_system_s2.jpg
  - title: 'LARGE VIEW #2'
    subtitle: ''
    text: ''
    image: /media/museum/photos/heathkit_et3400_system_s3.jpg
  - title: REAR SIDE
    subtitle: ''
    text: No connectors and no ability to save typed programs to a tape recorder.
    image: /media/museum/photos/heathkit_et3400_rearside_s1.jpg
  - title: MAIN BOARD
    subtitle: ''
    text: The upper part of the main board is covered by the case.
    image: /media/museum/photos/heathkit_et3400_mainboard_s1.jpg
  - title: MAIN BOARD CLOSE-UP
    subtitle: ''
    text: Each area of the circuitry is clearly marked.
    image: /media/museum/photos/heathkit_et3400_cloeup_s1.jpg
  - title: PROCESSOR CLOSE-UP
    subtitle: ''
    text: Here a 6802 version
    image: /media/museum/photos/heathkit_et3400_proccloseup_1.jpg
  - title: OPENED
    subtitle: ''
    text: A crude power supply unit is fixed to the hidden side of the main board.
    image: /media/museum/photos/heathkit_et3400_opened_s1.jpg
  - title: MANUALS
    subtitle: ''
    text: |-
      The ET-3400 was delivered with a full set of manuals and tests:\
      \- Microprocessors flipchart,\
      \- Two Assembly Language Programming Workbooks,\
      \- An hardware assembly manual,\
      \- A ten chapter reference book,\
      \- Two audio cassettes,\
      \- Two final exam kits(assembly language test and microprocessor test),\
      \- A poster sized schematic of the computer,\
      \- A parts pictorial illustration booklet.
    image: /media/museum/photos/heathkit_et3400_manuals_1.jpg
  emulators:
  - title: ET-3400 simulator
    url: http://www.pilgrimworks.com/trainer.htm
    platform: Windows
    text: ''
  links:
  - title: Heathkit ET-3400 Resources (Yahoo Groups)
    url: http://tech.groups.yahoo.com/group/ET-3400/
    text: Modifications, schematics, manuals and other resources for the Heathkit ET-3400 Microcomputer Learning System.
  comments:
  - author: Andrew L Ayers (USA)
    date: Saturday 9th March 2013
    text: Just picked up one of these trainers today at the Scottsdale ARC Hamfest$ got the trainer and a few mostly-complete "courses" (the trainer itself had some extra parts and whatnot on the breadboard, with wires running to various sections). I''ve been scouring the web looking for more info and such, and have found quite a lot. I found a PDF copy of EE-3401 - I''m looking for PDF copies of EE-3402 and EE-3405$ does anybody have ''em?
  - author: Michael Wagg (United states)
    date: Sunday 25th September 2011
    text: I currently have a complete set of the et-3400 manuals with tapes records and schematics on sale on eBay! They are in great condition. I have schematics as well as all Tests!
  - author: Tim Niles (Minnesota)
    date: Saturday 10th September 2011
    text: |-
      Would anyone on this topic know someone who owns the microprocessor continuing education manuals? I just sold the two manual set and the buyer discovered a couple of missing sections which I would rather replace somehow than just refund.

      Any help would be greatly apreciated.
  - author: Dave Harvey
    date: Sunday 4th September 2011
    text: Two more training courses which required the ET-3400 were the Voice Synthesis Course EE-3403-A and the 6809 Microprocessors Course EE-3404.
  - author: whipaway (USA)
    date: Sunday 9th November 2008
    text: |-
      Resources for ET-3400:\
      http://tech.groups.yahoo.com/group/ET-3400/
  - author: Kevin Sayler
    date: Monday 25th August 2008
    text: My kit came with 512 bytes of RAM, Looking at the schematic and part $s, I noticed that they were 1K x 4 RAM chips. A bit of rewiring doubled my kit''s memory
  - author: whipaway (Paisily Ppark)
    date: Sunday 22nd April 2007
    text: i have PDF files that show the modification, with diagrams.
  - author: Luposian (USA)
    date: Monday 12th February 2007
    text: I have a Heathkit ET-3400A, based on the 6808 CPU. I am thinking about upgrading it to the expansion connector, but the instructions aren't very clear and I'm not sure where it would show a visual on the assembly/wire-up for this connector. Can you help in this regard?
  - author: Martin Hultén Ashauer (Sweden)
    date: Friday 17th October 2003
    text: Me and my friend scored bigtime! I for a long time admired a ET-3400 computer located in a locker in one of the classrooms at my school. So one day my teacher told me that i could borrow it (this was like 2 weeks ago). Then after I had asked around a little another teacher led me and my friend to a classroom and opend a big cardboard box and lo and behold it containd over 10 more or less working ET-3400s. Then he went over and opend a locker and took out a fiew manuals, schematics and reffernce books. So on this monday (October 20:th 2003) my friend will get a car and drive home them beatifull blue boxes. Our joy is almost infinite!
  - author: Randy (Pittsburgh, PA)
    date: Wednesday 6th August 2003
    text: |-
      I have 3 of these ET-3400s in various states of disrepair. I also have extra parts. What I need is a schematic, manual and EPROM image.\
      Will trade a system for these items.
  oc_id: 785
  source:
    url: https://web.archive.org/web/20230510155752/http://www.old-computers.com/museum/computer.asp?c=785
    date: '2023-05-10'
---

The Heathkit/Zenith MicroComputer Learning System model ET-3400 was a very popular item designed to teach principles of computers and programming at Universities in the 1970s., and to educate the students of internal computer hardware and software components by self-assembly and programming the machine in pure Hexadecimal language.

It was delivered in assembled or Kit form. It also featured a prototype area and could be used as a design aid for developing special interface circuitry with common 6820 parallel interface or 6850 asynchronous chips.

Several software in ROM were also available. Among them an Assembler and a Tiny BASIC.

---

**Mendel Cooper's** memories:\
I built one of these from a kit back in about 1984, I guess. Price was approx. $200 in kit form.\
Heathkit used to sell three educational courses based on the ET-3400:\
1\) Microprocessor Course, EE-3401\
2\) Microprocessor Interfacing Course, EE-3402\
3\) Microprocessor Applications Course, EE-3405\
Using the specs in the manual, it was pretty easy to build homebrew memory expansion. For a couple of dollars worth of parts, I built a 2K module, using a 6116 (2K x 8) static RAM chip.

<table> <tr> <td></td> <td>We need more info about this computer ! If you designed, used, or have more info about this system, please send us pictures or anything you might find useful.</td> <td></td> </tr> </table>