I don't think you get a 32bit memory upgrade in an SX class system. It would most likely be 16bit... however that would be at CPU bus speed, not ISA speed, so 3x faster or so.

Right, my bad, but yeah...the ISA kills DOS4GW.

Some more eye candy...

Very modern design for 1988, build like a laptop. Gate arrays so no datasheet for chipset.
Do you have high resolution image of that ram expansion? 5 x 20 pin chips are suspicious, it might be something stupid like a PAL based full ram controller.
Options are:
Dynamic Ram 6 simm slots: 16 data + 11 address + 3 ras + 6 cas + we = 37 + grounds
CPU bus: 16 data + 23 address + r/w + oe = 41 + ground

50 pin connector is certainly too much pins for standard DRAM expansion, leading me to believe it might just expose CPU bus. That would let you expand ram with something silly like _one_ AS6C6416 8MB sram chip. Its expensive at $55, but cant beat simplicity 😀

Do you have any logic analyzers? or rpi pico? a good start would be slapping one on this connector and grabbing some logic captures. Making custom ram expansion looks pretty doable

rasz_pl wrote on 2026-11-06, 15:26:

Very modern design for 1988, build like a laptop. Gate arrays so no datasheet for chipset. Do you have high resolution image of […]
Show full quote

Very modern design for 1988, build like a laptop. Gate arrays so no datasheet for chipset.
Do you have high resolution image of that ram expansion? 5 x 20 pin chips are suspicious, it might be something stupid like a PAL based full ram controller.
Options are:
Dynamic Ram 6 simm slots: 16 data + 11 address + 3 ras + 6 cas + we = 37 + grounds
CPU bus: 16 data + 23 address + r/w + oe = 41 + ground

50 pin connector is certainly too much pins for standard DRAM expansion, leading me to believe it might just expose CPU bus. That would let you expand ram with something silly like _one_ AS6C6416 8MB sram chip. Its expensive at $55, but cant beat simplicity 😀

Do you have any logic analyzers? or rpi pico? a good start would be slapping one on this connector and grabbing some logic captures. Making custom ram expansion looks pretty doable

I agree the build quality on the interior is pretty impressive for the era, on par with the best of Dell and IBM offerings at the time. What I have been able to dig up in my research is these (sold only in the US, with MAXY being the Japan-only counterpart) were professional/industrial focused machines. This one arrived with a soundwave analyzing board (8-bit!) and appears to have been raided of several components before I picked it up on eBay. I can't tell for sure whether this one had a memory board or not by inspecting the header for signs of wear, but it did have a hard drive connected to a pretty pedestrian controller card I've since upgraded (no onboard IDE). The CMOS battery was also a wild one I've not been able to precisely source, so I had to find an equivalent and have introduced a CHECKSUM error I can't clear...but at least it keeps good time now. 😎

I wish I had a better photo of the memory board, but sadly that is the best I've been able to turn up. No logic analyzers or RPI Pico here, but I'd be down to pick up some gear to pull readings and figure this out. I'm crap at soldering, but I can cobble together parts and gather readings with the best of them.

Seeing how much performance I can get out of this little engine is kind of a bucket list thing for me since, as of now, it's completely hamstrung paging memory across the ISA bus. Doom is hilarious until you make the screen size a literal postage stamp. 😆

get a $5 pico and ill help you sniff ram expansion connector - will require getting matching plug or soldering bunch of wires on the back and running system out of case for a while

>introduced a CHECKSUM error I can't clear

dump bios and we can figure that one out too 😀 Hoe does the Bios setup look like?

There is zero info about Mitsubishi "walsy1-1" on English speaking internet. https://theretroweb.com/motherboards/s/mitsubishi-mp3300 looks similar but not really, like someone drew it from verbal description 😀

Does your case also state mp3300 on the back like https://wiki.preterhuman.net/Mitsubishi_MP_386S?

Was anything ever connected to JF2?

rasz_pl wrote on 2026-11-06, 17:25:

get a $5 pico and ill help you sniff ram expansion connector - will require getting matching plug or soldering bunch of wires on […]
Show full quote

get a $5 pico and ill help you sniff ram expansion connector - will require getting matching plug or soldering bunch of wires on the back and running system out of case for a while

>introduced a CHECKSUM error I can't clear

dump bios and we can figure that one out too 😀 Hoe does the Bios setup look like?

There is zero info about Mitsubishi "walsy1-1" on English speaking internet. https://theretroweb.com/motherboards/s/mitsubishi-mp3300 looks similar but not really, like someone drew it from verbal description 😀

Does your case also state mp3300 on the back like https://wiki.preterhuman.net/Mitsubishi_MP_386S?

Was anything ever connected to JF2?

It is indeed an MP-3300, though the documentation and diagram from theretroweb.com only line up at a 20,000' level. That 32-bit memory slot is obviously misplaced, and there are no jumpers/switches on the board I can find anywhere. Mine arrived with nothing connected to JF2, and I haven't been able to find details on what it is for.

I'll dump the BIOS and message about that later today if I can, this weekend for sure. Which Pico do you recommend I pick up?

2x cheapest standard pinout pico 1/2. You will also need 2x usb cables so either official picos + mini usb, or clones + USB 3 cables, whatever you already have.

J25 connector is imo unobtanium, looks very close to 50 Pin Mini D ribbon (used for laptop printer port sometimes?)
https://www.ebay.com/itm/195977201948?var=495835011357 https://www.ebay.com/itm/235271973398?var=535302794732
pin pitch matches, but wont mate unless original connector plastic case gets snipped away.
Cant find its matching pair in pcb version, only cable.
Ideal would be finding right angled PCI (old school, not pcie) connector, but those dont seem to exist either. How is the space above it in the case? is there space to plug card perpendicularly or is there disk, metal or something else above it? if there is space you could totally solder cut to size PCI connector, then potential ram board could be plugged into that.

Personally I would desolder J25 connector and
-directly solder cables to two picos for capturing
or
-2.54mm single row headers. Those wont fit soldered normally next to each other, have to solder one row and then pull off plastic before soldering next one. Pulling off plastic will be VERY annoying. Finally connect to picos with short dupond cables.

If/when signaling turns out obvious you can solder directly board to board using same 2.54mm header pins. If not can just snip them away.

rasz_pl wrote on 2026-11-06, 21:15:

2x cheapest standard pinout pico 1/2. You will also need 2x usb cables so either official picos + mini usb, or clones + USB 3 ca […]
Show full quote

2x cheapest standard pinout pico 1/2. You will also need 2x usb cables so either official picos + mini usb, or clones + USB 3 cables, whatever you already have.

J25 connector is imo unobtanium, looks very close to 50 Pin Mini D ribbon (used for laptop printer port sometimes?)
https://www.ebay.com/itm/195977201948?var=495835011357 https://www.ebay.com/itm/235271973398?var=535302794732
pin pitch matches, but wont mate unless original connector plastic case gets snipped away.
Cant find its matching pair in pcb version, only cable.
Ideal would be finding right angled PCI (old school, not pcie) connector, but those dont seem to exist either. How is the space above it in the case? is there space to plug card perpendicularly or is there disk, metal or something else above it? if there is space you could totally solder cut to size PCI connector, then potential ram board could be plugged into that.

Personally I would desolder J25 connector and
-directly solder cables to two picos for capturing
or
-2.54mm single row headers. Those wont fit soldered normally next to each other, have to solder one row and then pull off plastic before soldering next one. Pulling off plastic will be VERY annoying. Finally connect to picos with short dupond cables.

If/when signaling turns out obvious you can solder directly board to board using same 2.54mm header pins. If not can just snip them away.

Copy that. Give me a week or so to acquire the gear, and I'll get to do the things. Could we go the route of soldering to the posts on the bottom of the board to avoid removing the header?

There's about 5.5" of space between the board and the top of the case, and another inch below the board to the bottom of the chassis.

BIOS dump link is in your PM.

Thanks so much for the assistance here. Really kind!!

ralphmaif wrote on 2026-11-06, 22:09:

Could we go the route of soldering to the posts on the bottom of the board to avoid removing the header?

You do you 😀 imo desoldering would be much easier. Problem with back is you cant just solder long dangling wires as this is either CPU or RAM bus and those will create EMI and make computer crashy/not booting. For probing to make sense computer needs to run normally, ideally running test programs poking at ram.

Realistically you will never plug anything into it, maybe that ebay '50 Pin MDR' plug (https://www.aliexpress.com/i/2251832762922789.html) after cutting half of the connector off. ...hmmm, wait - pulling that plug out of metal shroud would work! didnt think of that at first 😀 Might need some arts and crafts, hot glue and cardboard, to make it align 😀 That would be much better than soldering wires at the back and in case of success connector can be later reused.

ralphmaif wrote on 2026-11-06, 22:09:

BIOS dump link is in your PM.

failed dump, its all FFs and 7Fs
try this ai slop https://drive.google.com/u/0/uc?id=1RVtJVhDKW … export=download https://www.youtube.com/watch?v=FAxQU07O4E4 bonus points afaik it also dumps CMOS

rasz_pl wrote on 2026-11-07, 01:01:

You do you :) imo desoldering would be much easier. Problem with back is you cant just solder long dangling wires as this is eit […]
Show full quote

ralphmaif wrote on 2026-11-06, 22:09:

Could we go the route of soldering to the posts on the bottom of the board to avoid removing the header?

You do you 😀 imo desoldering would be much easier. Problem with back is you cant just solder long dangling wires as this is either CPU or RAM bus and those will create EMI and make computer crashy/not booting. For probing to make sense computer needs to run normally, ideally running test programs poking at ram.

Realistically you will never plug anything into it, maybe that ebay '50 Pin MDR' plug (https://www.aliexpress.com/i/2251832762922789.html) after cutting half of the connector off. ...hmmm, wait - pulling that plug out of metal shroud would work! didnt think of that at first 😀 Might need some arts and crafts, hot glue and cardboard, to make it align 😀 That would be much better than soldering wires at the back and in case of success connector can be later reused.

ralphmaif wrote on 2026-11-06, 22:09:

BIOS dump link is in your PM.

failed dump, its all FFs and 7Fs
try this ai slop https://drive.google.com/u/0/uc?id=1RVtJVhDKW … export=download https://www.youtube.com/watch?v=FAxQU07O4E4 bonus points afaik it also dumps CMOS

Yeah, that trick with the MDR might be an option and is worth trying out. I'll probably just need to get over myself and try desoldering to do it right.

Bummer on the BIOS dump! I'll give it another go with the link you sent.

rasz_pl wrote on 2026-11-07, 01:01:

You do you :) imo desoldering would be much easier. Problem with back is you cant just solder long dangling wires as this is eit […]
Show full quote

ralphmaif wrote on 2026-11-06, 22:09:

Could we go the route of soldering to the posts on the bottom of the board to avoid removing the header?

You do you 😀 imo desoldering would be much easier. Problem with back is you cant just solder long dangling wires as this is either CPU or RAM bus and those will create EMI and make computer crashy/not booting. For probing to make sense computer needs to run normally, ideally running test programs poking at ram.

Realistically you will never plug anything into it, maybe that ebay '50 Pin MDR' plug (https://www.aliexpress.com/i/2251832762922789.html) after cutting half of the connector off. ...hmmm, wait - pulling that plug out of metal shroud would work! didnt think of that at first 😀 Might need some arts and crafts, hot glue and cardboard, to make it align 😀 That would be much better than soldering wires at the back and in case of success connector can be later reused.

ralphmaif wrote on 2026-11-06, 22:09:

BIOS dump link is in your PM.

failed dump, its all FFs and 7Fs
try this ai slop https://drive.google.com/u/0/uc?id=1RVtJVhDKW … export=download https://www.youtube.com/watch?v=FAxQU07O4E4 bonus points afaik it also dumps CMOS

I don't think desoldering is necessary now! 😎

Found the connector on eBay, and it seems to fit perfectly into the slot on the board, leaving 50 exposed pins to probe with the pico2 boards.

The ram soldered to the board appears to be very low density.
But the code should be 4 megabit with 20 chips thats a fair bit of ram, not a megabyte

If the onboard memory controller can handle it and the memory dipps come in a higher density it's possible you could desolder all that mess.

Would need tech and diagnostic manuals to validate first

I think it's 2MB of RAM in aggregate between what's soldered to the front and to the back of the motherboard.