Uploaded December 2020 | Updated September 2026, 3 weeks ago
In this video, I build a clone of the ET-3404 adapter board for the ET-3400/ET-3400A. This board replaces the trainer's original microprocessor (at 6800 for the 3400 or a 6808 for the 3400A) with a 6809P. The new microprocessor is not binary compatible and therefore comes with a new ROM image as well for the machine monitor.
Blog Post: smbaker.com/cloning-the-et-3404-6809-adapter-for-the-heathkit-et-3400
Along the way I also encountered several "bad" 6809P ICs. You have to be careful when building these boards that you don't also run into bad ICs, as there seems to be many out there in the wild -- I've heard the same from other ET-3400 enthusiasts. I originally thought they were counterfeit (not shown in the video -- I performed tests and they behaved more like a 6809E without the clock generator than a 6809P with), but once I received another shipment of ICs from china, which included a mix of good and bad identically marked chips, my opinion became that many of them were simply bad.
For more electronics projects, see smbaker.com
In this video, I build a clone of the ET-3404 adapter board for the ET-3400/ET-3400A. This board replaces the trainer's original microprocessor (at 6800 for the 3400 or a 6808 for the 3400A) with a 6809P. The new microprocessor is not binary compatible and therefore comes with a new ROM image as well for the machine monitor.
Blog Post: smbaker.com/cloning-the-et-3404-6809-adapter-for-the-heathkit-et-3400
Along the way I also encountered several "bad" 6809P ICs. You have to be careful when building these boards that you don't also run into bad ICs, as there seems to be many out there in the wild -- I've heard the same from other ET-3400 enthusiasts. I originally thought they were counterfeit (not shown in the video -- I performed tests and they behaved more like a 6809E without the clock generator than a 6809P with), but once I received another shipment of ICs from china, which included a mix of good and bad identically marked chips, my opinion became that many of them were simply bad.
For more electronics projects, see smbaker.com
