ETA-3400 Memory/IO Clone Bare PCBOARD for Heathkit ET-3400 Trainer

Description

This BARE PCBOARD is to use to build a clone of the ETA-3400 memory/IO accessory for the Heathkit ET-3400 trainer. This clone uses modern components (62256 SRAM, 28C64 EEPROM, PLD logic array for address decoding, etc). The BOM, schematics, etc., are up on my web page, which is linked to the attached youtube video. This is only a bare PCBOARD -- additional components and significant skill is required to assemble. In particular, you will need to be able to program an EEPROM and a programmable logic device. The commonly available TL866/minipro programmer is sufficient to program both of these devices. You will need to be proficient in soldering, and you will need to be able to source and purchase all of the components to complete the project. The BOM includes digikey links for most components, the one notable exception is the 6821 PIA which you can typically find on eBay.
Heathkit ET-3400 Part 1: Designing and building an ETA-3400 Memory/IO Accessory
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Serial IO is intended to be connected via a DB25 on the back, or as an alternative, a Raspberry Pi Zero W may be installed internally and used as a terminal.
Your ET-3400 will need to be equipped with the 40-pin expansion connector to use a memory/IO board. To do so may require modification of your trainer -- the official heathkit instructions are available online that show how to do this, it is a little more complicated than simply adding the header to a trainer as some wires need to be added.
This is my latest pcboard design, revision 0.10.
NOTE: I have tested this board on my ET-3400 trainer and on my ET-3400-A trainer. The trainer can be a bit picky about the static ram that is used. The recommended part in my BOM is a 70ns AS6C62256A-70PCN. 55ns (slightly faster) of the same part was confirmed to not work. Other SRAM chips by other manufacturers may be hit or miss. With the recommended RAM, I did run a basic program continuously on the trainer for several days before powering it down.
You should consider this project to be in alpha state, possibly requiring some diagnostic effort if it doesn't immediately work for you.
NOTE 2: These boards should be considered as-is, without technical support (Unfortunately I simply don't have the time). If you purchase these boards, you will be responsible for diagnosing any problems yourself. You should probably watch my video and visit my website / review the schematics prior to purchase.