Maybe the extra RAM can only be used as EMS or RAMdrive.
Most of the 286s I know of with 8-bit slots are limited to only 1MB of directly addressable memory.

you maybe right, someone else suggest me the same.
i tried to see with qram if something happen, but it's a no go, it just hang when run optimize for the first time.
i don't know if he require something more proprietary driver. if you know something i can try ?
he actually run pc dos 7.

for the 8 bit slots, i think it's mostly because the chassis don't allow 16 bit to fit... they reused the same chassis as the MBC 16/17 series, and it's a short one.
the motherboard itself is very short.

if this can help, he use a phoenix bios version 1.02.10 - 01. with a very minimalistic setup menu, just for set time and date, and confirm if 287 is here or not.
and the chipset seems to be a chips and technologies F82C230.

hmmm i finally found something about the chipset... and in fact, this machine is more a PS/2 model 30 8086 clone than an AT.
http://www.bitsavers.org/components/chipsAndT … orm_Catalog.pdf

so, you think sanyo made the choice to only limit extra ram as ems only ?
sad they don't say anything about this in their manual.

Hi Whaka, I don't suppose you have the manuals and disk images avaialble? I have one of these but no disks so I can't change any BIOS settings.

Good afternoon, dear friends! I apologize in advance for my poor English 😀
I am forced to ask for advice, because I can't think of anything else.
I received such a board (see photo) - Sanyo MBC-17Plus, also known as Sanyo SAT-201B. At first, I wanted to dismantle it and use it as a donor of microcircuits. Because it did not show any (at all) signs of life. The VGA/EGA board did not initialize. As it turned out, the Sanyo BIOS does not write any POST codes to port 80h and does not even give a sound indication of POST errors.
There is very little documentation for this board. It all boils down to configuring a few jumpers and one DIP switch.
However, after checking the oscillograms of the data bus and the address bus, I thought that the patient had a chance to live. And indeed, when I used HGC instead of a VGA or EGA card - Sanyo started! It also started with a CGA card without any problems. I thought: "Okay, there are some problems with the initialization of the EGA/VGA BIOS, or problems with finding extensions at address C000h". Moreover, the Sanyo also refused to see the XT-IDE card, configured for Dx00h.
Having replaced the original BIOS with Supersoft/Landmark Diagnostic ROM, I managed to test the board. No errors were found. At the same time, I remembered the "features" of the Landmark ROM regarding the so-called "self-initializing" VGA cards. And indeed, as it turned out later, with some VGA and EGA cards Sanyo MBC-17 works fine. And with some - it refuses outright. Maybe someday I'll check with my entire collection and publish the statistics, but that'll be later.
I should also add that this board requires a working battery to start. It doesn't give out "Battery state low" notifications, it just freezes.. Strange... But that's not a problem - I unsoldered the connectors and connected a new battery, along with the keyboard and speaker.
But that's where my luck ended... I connected the floppy drive - it won't boot... I tried booting with a 3.5''-1.44Mb floppy drive, a 5.25''-1.2Mb, and a 5.25''-360Kb floppy drive. The "Floppy drive seek at boot" procedure runs normally, after which the floppy drive makes a few head movements - and that's it. It freezes. I tried with different floppy disks (MS-DOS v.3.3, MS-DOS v.5.0, MS-DOS v.6.22, EZ-DOS, CP/M-86) - the same result. I tried with the original floppy disk that came with the Sanyo MBC-17 (actually MS-DOS v.3.20), and contained some utilities for working with hard disks - the same result. The floppy drive makes a few head movements - and that's all. It freezes.
Okay, I thought. Maybe the problem is in the disk drive controller (WD37C65) built into the MBC. I turned off the built-in FDC with jumpers, tried with external FDC cards. With several different FDCs (37C65, as well as with 82077 and some others...) - the result is the same. The disk drive makes a few movements with its heads - and that's it. It freezes.
Having lost hope of booting from a floppy drive, I decided to try hard drives. Since this Sanyo did not want to “see” XT-IDE, I used the most ordinary 16-bit IDE card. It is clear that large hard drives should not even be tried to be connected without XT-IDE, so I took the “correct”, “reference” ST351A/X.
By the way, I have a strong suspicion that the hard disk parameter table in the Sanyo MBC-17 BIOS is somewhat different from the usual ones used in AMI BIOS, Award BIOS, etc. But I have no way to check this - so maybe I'm wrong.
Nevertheless, using a regular 16-bit IDE card and ST351A/X, the process started, but only at first glance. The hard disk moved its heads more actively, blinked the LED indicator, and even issued a notification "Starting MS-DOS". But that's where all the progress ended, the boot did not reach completion, everything froze ...
I repeated these attempts with other hard drives (Miniscribe 8051A, Western Digital 95044-A, WD Caviar280). And the same, with different operating systems. The result is the same - everything freezes on the notification "Starting MS-DOS" or "Loading CPM.SYS".
Almost in despair, I decided to try to boot from MFM hard drives. Given the nuances with the initialization of VGA/EGA cards and problems with XT-IDE, I expected problems with the BIOS initialization of 16-bit MFM cards. But, surprisingly, with two MFM controllers (Cirrus Logic CL-SH260 and Western Digital WD 42C22A) and with two hard drives (Seagate ST-125 and Miniscribe 8425F), Sanyo "found a common language". But only for a short time. It all ended the same - everything hangs on the notification "Starting MS-DOS" or "Loading CPM.SYS".
At this point I gave up trying to get the Sanyo MBC-17 to boot normally. Of course, I had the idea to try SCSI adapter like the AHA-1520/1522 or AHA-1540/1542. But I think the result would be the same...
In addition, I suspected that the problem might be in the Sanyo MBC-17Plus BIOS firmware. I found several BIOS versions for this board - both slightly older than mine and slightly newer. I tried them all - the result was the same...
I tried to get it to work with various early versions of Phoenix BIOS, Award BIOS, AMI BIOS. I couldn't get any improvement with any of them, on the contrary. With almost all the "foreign" BIOSes I received messages about errors in determining the amount of RAM.
I'm giving up ((( But I put so much effort into this board – that I just don't want to back down. Has anyone encountered similar boards? Has anyone observed similar problems? – I would be very grateful for advice !!!

Supersoft/Landmark Diagnostic ROM is really bad when it comes to testing ram, and everything points at bad ram
try flashing this one https://github.com/ki3v/xtramtest

rasz_pl wrote on 2026-06-19, 22:21:

Supersoft/Landmark Diagnostic ROM is really bad when it comes to testing ram, and everything points at bad ram
try flashing this one https://github.com/ki3v/xtramtest

Are you sure this diagnostic ROM will work if used as a BIOS extension on a 286 motherboard? - I tried running Ruud's diagnostic ROM - it didn't work, it won't start.

Vlodek_d wrote on Today, 17:03:

rasz_pl wrote on 2026-06-19, 22:21:

Supersoft/Landmark Diagnostic ROM is really bad when it comes to testing ram, and everything points at bad ram
try flashing this one https://github.com/ki3v/xtramtest

Are you sure this diagnostic ROM will work if used as a BIOS extension on a 286 motherboard? - I tried running Ruud's diagnostic ROM - it didn't work, it won't start.

As i know - diagnostic ROM is BIOS replacement not BIOS extension

Babasha wrote on 54 minutes ago:

As i know - diagnostic ROM is BIOS replacement not BIOS extension

"Method 2: Installing as an "option ROM"
The second way this ROM can be used is by installing it as an "option ROM". The exact method of preparing a ROM chip will vary (and is currently left as an exercise for the reader, as they say), but it is the same as preparing any other option ROM such as XT-IDE.
Once the EPROM is prepared, it can be installed in any option ROM socket on the motherboard. Depending on your BIOS, you may be able to install the option ROM in the BASIC ROM socket (which will generally be empty on clones and filled on actual IBM PC/XT computers).
Then, when booting any BIOS that supports option ROMs, the BIOS will initialize this ROM, which will install itself as a warm start handler, and when the BIOS attempts to boot the operating system, this BIOS will print a message asking you to press the T key to start RAM tests, or any other key (or just wait a few seconds) to continue booting.
If there are other boot-providing option ROMs in the system (such as XT-IDE or network cards with boot ROMs) which are loaded at higher addresses, they will be given an opportunity to boot first, and they may not permit the XTRAMTEST ROM a chance to take over, so you may have to remove other cards in order to get this ROM to run in option ROM mode."

I quoted the Github of the author of the specified project.