Finally the XT 5160 motherboard seems stable! The cause of my grief was a 74LS00 with bad a bad output, involved in the DRAM address generation circuitry. Snapped it away and running multiple rounds of tests now.

Next week I'll have some writing to do I guess... Got tired of blindly swapping around DRAM chips to find good ones, and I don't like connecting/disconnecting shields on arduinos. So I've just drawn an all-in-one tester for 4164 and 41256 for my necessities. It won't stress test the chips at high speed, but will be enough to weed out dead/obviously broken ones.

Finally maxed out the RAM on this 286 (4 Megs!).
Now I just need to wait for the PCBs of the EMS board...

Just replaced all the tantalum caps on this 5160 : one of them gave up the ghost before I got it, so I swapped all of them with ceramics. I also replaced the socket for the RAM decoding PROM, to ease my work for a future 1mb expansion.

Just drawn another board. Just to come out clean, this is not (fully) a project of mine: I just took the lo-tech EMS board (, added more RAM (4 Meg total), made it through-hole, added an optional ROM socket and a LED to indicate when the RAM is active.
I plan to use this to have hardware EMS+XMS in my 286. As usual, will release everything once I build it and verify that it is mostly working!

Found out that the Winbond chipset on this 286 mobo has embedded EMS mode for RAM above 640k (if you load an ad hoc sys module and configure the option in the BIOS). The sad part is that I found no way in hell to gain upper memory, with the exception of wasting ALL the EMS memory for it. Gah!

Ew, pretty busy , but had some time for yet another iteration of my serial/parallel ISA card.
I replaced the two 16C550 with a single 16C554 (for a total of 4 serial ports!) and added circuitry for an expansion ROM (going to save me an ISA slot on a few 286/386 machines).

Will ponder on this one a bit, and if everything looks fine I'll send it for production in a week!

Not really proud of the result, but now both cards have a bracket. Oh, I also flashed the original DSP firmware from here:

Yup, the complete one (two clones) works! The other I have yet to test (and I lack one SAA1099 chip). Now I need to think how to handle building the brackets for these. Drilling them is going to be a ...

Back at my old place today, rummaging around the storage room me and my father share. Found a handful of CPUs, old cables, internal pc speakers, old floppy drives...

New keyboard for my clone built and installed. And this time I did not mess up the footprints!

I think I'm almost at the end of the testing for my dual UART + Parallel port card: reorganized the pinout for the parport header and updated the IRQ logic to match the schematics of the IBM AT. Now every diagnostic I throw at it passes without issues. Time to prepare to print a rev 1.1 and then release?

Interesting that my autocorrector replaced "need" with "nerd". Still, not so wrong...

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Two tools I'll nerd to get my PS/2 up and running: an MCGA connector adapter and a floppy adapter, so I'll be able to use an emulator to load the configuration software.

Built two boards by Sergey. One I will keep as a spare to test cards, the other is going to be part of a longer term project (want to do another XT build: plain 8088 this time, no V20, game blaster clone audio.. Maybe an EGA card if I can find it)

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