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I assume you meant radial, C20 is the only one that's axial in that list. Some corrections from my board: C2 - 100uF 25V C3 - 220uF 25V C20 - 470uF 25V

That bridge rectifier almost makes me think it could take low voltage AC. I've owned a few things that could take either AC or DC at the same voltage.

Here's the fixed 512Kbit boards attached. My 1Mbit panels finally arrived. Next time I'm making smaller panels...

Not easily. See the below image, you would have to cut the traces at the blue lines and bodge the green connections. Possible if you have a steady hand and patience I suppose.

It looks like there's a duplicate pin that ended up on the layout for the 512Kbit chips. I'll adjust it now. I haven't been able build the 512Kbit boards, I'm still waiting on the panels for the 1Mbit boards to get here...

I've tested it on the SST39SF010A so far, but it should work fine on the AT27C010 and MX27C1000, theoretically it should even work on the AT27C020 despite it being 2Mb chip.

Here's the copy I have of Vol. 4. My Windows 98 computer used for EPROMs died so I had to buy a USB to IDE adapter to get to it, but it's likely still intact.

No, I haven't. I can post them but they're on another computer so I'll have to find a time to either switch to that computer or dump them again.

It looks like the dump might be missing four bytes somewhere in the middle, since earlier data seems to be offset by four bytes as well. It's possible it may still work, but I haven't tested that dump since it looked different than my dump.

So far I haven't run into any issue burning the smaller roms to the 1M chips.

This is the 1MB board with Vol. 4 on an SST39SF010A. I'm going to try the other 4 roms on it later.

Just got one of the new boards assembled. Initial tests look fine.

Here's the updated boards. Hopefully dimensional accuracy is still good on the new connector footprint. I'm waiting to get another board to test with now, should hopefully be this week. I've also ordered a solder stencil this time so I don't just have to spread paste and pray. The 1Mbit boards...

Yeah it looks like the custom footprint came out backwards. My boards were held up due to a four layer board that was in the same order, but they finally arrived. I was able to put one together by bending the pins, and it does appear to work. I'll have to correct the footprint for the connector...

If I measured correctly it should be an 0805 resistor. Looks like you have size 0402. Anything from here should work: https://www.mouser.com/c/passive-components/resistors/?case%20code%20-%20in=0805&resistance=10%20kOhms&instock=y&sort=pricing

I have to wonder if the designers of the TechStep intended for different connections to be released in the future, considering that the entire IO section on the TechStep is detachable.

I usually order a good bit because the volume discounts are sometimes as much as 50% off. Either that or buying full reels for that pick and place machine I hope will arrive someday. Most of the expense in that order was the 160 STM microprocessors, and parts to build a new logic board for a...

It's no big deal, I'll just have to find something else to use the extras on someday.

I guess I'll order some boards and parts as well, not like it will make much of a difference adding to my already $750 LCSC order.... Edit: I now realize I am very stupid and have ordered the 100 of the EEPROM twice, first from Mouser and now from LCSC. Maybe someday I'll switch to BOM software...

Here's the one for the AM27C512 pinout, as well as variations for the M95020-WMN6TP EEPROM chip, which I think is a compatible replacement for the X25C02P.