I've revisited this board, and the repair work needed to restore proper hardware turbo functionality and fix the random BIOS crashes was quite substantial indeed...

To summarize what I had to do:
- Additional reflow work on the U4800 chipset
- Replaced the 2N3906 in the reset circuit and one 10K resistor that looked mangled
- Replaced the 74FCT244 with a 74F244
- Replaced a round pinned TTL socket that I had added, with a double wipe
- Jump a broken via (my fault) on the socket with a wire

Now it POSTs more reliably and seems to run quite a lot more stable. The turbo switch works too. What's planned for this board, is to replace the broken SIMM slots.

Congratulations beautiful card, I love the 386, I recently got a dx-40 that I fixed, then I recovered the 386SX-33 and restarted after more than 15 years, finally I recovered an MB386-DX from Atronics (ATi) which i should rebuild and repair asap.
If you need help with solving please ask, if you want to see my boards repaired and others under repair you can find them here:
Re: Test and troubleshoot PC@LIVE motherboards
I hope you find something that can be useful to you.

Hello !

Your board's manual can be found here https://www.ultimateretro.net/en/motherboards/4357
Could you please provide a BIOS dump and a good picture of the front of the board ? (And don't forget to remove the watermark with the date !) 😀

Thanks !

Re-visiting this board AGAIN... inconsistent POST issues *persist*! Issue is, the board often comes up stone dead ('-- --' on the POST probe) and will stay that way until I whack the reset button a couple of times.
After replacing almost everything else pertinent except the U4800 chipset, 14.3MHz osc and TTLs, I decided to try replacing the 82C206 chip as that holds the reset circuitry inside. Replaced with a CHIPS P82C206, and now the board never sticks on '-- --' anymore... but there seems to be something wrong with the P82C206 chip I used as it now beeps with 10 beeps (CMOS shutdown/reset register error). I'll get a different 82C206 from a different supplier, and re-try the arduous surface-mount-solder-by-soldering-iron trick again later... >_>

At least I'm onto something here, as it's never turning on 'stone dead' anymore...

Here's the BIOS. AMIBIOS 12/12/91 apparently.

After the mild disappointment of the otherwise now quite-well working Morse M3 386DX board that cannot reliably handle 40MHz, I decided to revisit this board. Still waiting for the PLCC surface mount socket and 82C206 to arrive, but in the meantime I fixed those broken SIMM slots. The 82C206 was removed. That ups my count to no less than six faulty 82C206 chips on hand. 😜

Sockets finally arrived; fitted one to the exposed solder pads. Kind of aping Shoestring on Jammarcade.net for the method of soldering a 'slightly' modified surface mount socket, but this is all I can do with just a soldering iron (and lots of flux).

Now all that's left to do, is find an 82C206 that isn't dead, and do some testing.

Success! After fitting a new 82C206 the motherboard now POSTs without needing me to press the Reset button repeatedly. I'd call that a success.

Also the four replacement SIMM slots are working fine. I get 8MB when I insert eight 1MB sticks.

One quirk about this board though: it only seems to want to work with 256K cache set in Write-Through. The TH'99 jumper settings and the settings on the board for 256K cache, are the same between Write Back and Write Through modes, which doesn't seem right. It wouldn't work with 64K or 128K in either mode, too, so something's still messed up (probably jumpers). But with 256K it works alright.

The Chips 82C206 didn't like 10MHz ISA much, so I swapped it with a UMC one from another board... am now testing 10MHz ISA with it.

Well it works pretty well at 10MHz ISA, except for my PS/2 mouse card. After a few minutes the mouse stops responding until I leave Windows. Weird issue.
For now I've set it back to 8MHz ISA.