Search Posts:

Heathkit ET-3400 / ETA-3400 Expansion


Return to Threads

  Heathkit ET-3400 / ETA-3400 Expansion by Bill Degnan - 02/18/2014 14:14
Heathkit ETA-3400 Expansion Unit
View of the Heathkit ETA-3400 mainboard. The ETA-3400 expansion unit was an add-on to the ET-3400 6809-based trainer. Click image for larger view.

Rear ports Heathkit ETA-3400
Rear ports include cassette and RS232/teletype connectors. Click image for larger view.

Initiated a project to add an ETA-3400 to a Heathkit ET-3400. The main computer seems to work fine. Step one, complete the connector cable from parts on hand. With additional RAM and I/O ports, the ET-3400 becomes a lot more useful. I have downloaded all of the necessary docs. More to come.

More photos

  ET-3400 Mods Complete by Bill Degnan - 03/05/2014 14:17
Heathkit ET-3400 40 pin dual connector installed.
Heathkit ET-3400 40 pin port. Following the modification kit directions I installed a dual connector. Click image for larger view.

Heathkit ET-3400 4.00mhz crystal added
Next a 4.00mhz crystal was installed on the top side of the ET-3400 motherboard, with a 1000ohm resistor and 22pF cap, similar to the mod guide. Click image for larger view.

ET-3400 wiring modifications
I did not have the ribbon cable that would have originally been supplied by Heathkit, so I improvised and installed each wire individually. I also could not find a GD510 diode as described in the mod guide. Asking around, I got advice from Dan R. to use a shottky diode 1N5817 instead. It's hard to see, but it's attached to pins 6 and 35 of the under side of the 40 pin cable connector. Click image for larger view.

Heathkit ET-3400 motherboard power leads
A number of power leads were brittle and popped off as I was working, so I re-attached them on the underside of the board. Click image for larger view.

Heathkit ET-3400 and ETA-3400
Heathkit ET-3400 and ETA-3400, re-assembled. Click image for larger view.

Heathkit 6809 Monitor and Heathkit (Pittman) Tiny BASIC
Modifications completed. Pictured here is an image from terminal emulator Teraterm that displays operation of the ET-3400 running Heathkit 6809 Monitor and Heathkit (Pittman) Tiny BASIC. The physical terminal connection is made from the rear of the ETA-3400. Click image for larger view.


  How to Load Monitor and Tiny BASIC by Bill Degnan - 04/03/2014 22:59
1. I have baud rate toggle mod installed on the front of my ETA-3400. Position 4 corresponds to 2400 baud. I set my terminal to match: 2400/7/N/2.

2. Next I hit the DO button and entered the memory location for the ROM monitor - 1400. I was greeted with a MON> prompt. Great. From there I can run whatever Heath 6809 monitor commands.

3. After playing around with the monitor I activated Pittman's Tiny BASIC by running the following command at the monitor prompt:

G 1C00

The computer responded with a : prompt. Check early Kilobaud mags for sample programs, or consult the software manual.



Buy a Commodore Computer Poster

Popular Topics and FAQs

  • Commodore B Series Tips and Tricks
  • Aerocomp TRS 80 M 1 Expansion Unit DDC
  • Items Wanted
  • Lobo Max 80
  • Zenith Z-19-CN
  • Prototype PET 2001 photo
  • Using Toggle Switches to Analyze Memory
  • Commodore Disk Archive Project
  • PET 2001 Prototype at Gametronics 1977
  • Jim Butterfield Photo
  • IMSAI 8080 With Processor Tech. Cutter
  • Secrecy is the keystone of all tyranny
  • Cromemco System Three
  • Northstar Horizon - Boot Problem
  • Computer History and Restoration Links
  • Commodore BX-256-80 - 8088 Co-processor
  • S-100 board testing with Z-80 ICE
  • Donner 3500 - an early portable computer
  • Digital (DEC) PDP 11/05 NC Assembly
  • Univac 1219 rescue
  • Fido BBS listing node list 6-13-1986
  • PDP 8e
  • MITS 88-2 SIO (2SIO) for BASIC
  • Visual Technology Inc Model 1050
  • Amiga 2500 Restoration
  • The Evolution Of IBM Computers
  • Replacement teletype print hammer head
  • Archiving and Copying Software 101
  • Computers Built 1940 - 1950
  • CBM B-520 (a.k.a B256-80 or B500 256)
  • RCA COSMAC Microkit
  • Commodore 64K C-116 Mods
  • MITS 8800b Turnmon 9600 baud
  • Catweasel, 8in and 5 1/4
  • Raspberry Pi as Gateway to Internet
  • Digital PDP11 late 1969 early 1970
  • PDP 11/40 72 inch cabinet model
  • PDP 11/40 Industrial 11 model
  • Digitial MicroVAX 3100 30 System
  • Digital VAX 4000-200
  • Commodore 64 / 1541 DRIVEKNOCK
  • Booting the System Using RL02 drive
  • PACS: Reflections by Kathleen Mauchly
  • Tele-Graphic Computer Systems Inc.
  • Commodore B Series SID Jukebox?
  • Installing Core into PDP 11/40
  • Setting Up OpenVMS 7.1 DNS CLERK
  • Felt-Tarrant Comptometer Model J
  • NextStation Color
  • Digital Rainbow (PC100-B2)
  • 1970 Compusad Compulogical Tutor
  • Archiving Papertapes Using DSI NC 2400
  • 1976 P.C.C. Features the MAI JOLT 6502
  • 1961 Beckman DEXTIR Computer
  • UNIVAC 1 and UNIVAC File Computer 1
  • Past Issues:

    electronic brain homeostat quadruple coil

    This image was selected at random from the archive. Click image for more photos and files from this set.