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 include cassette and RS232/teletype connectors. Click image for larger view.

Heathkit ET-3400 40 pin port. Following the modification kit directions I installed a dual connector. Click image for larger view.

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.

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.

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, re-assembled. Click image for larger view.

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.