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Heathkit ET-3400 / ETA-3400 Expansion


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  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.



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