Sorry for necroposting, but this is SYSTEM 302 Motherboard https://stason.org/TULARC/pc/motherboards/I/I … SYSTEM-302.html
Full documentation https://archive.org/details/bitsavers_intelda … eJan90_12579092.
Attached BIOS from my mobo, but U79 seems to be broken, every time I reread the chip on TL866 I have a new value 🙁
But the motherboard booting and I see a BIOS screen.

silentw wrote on 2021-03-24, 13:18:

Attached BIOS from my mobo, but U79 seems to be broken, every time I reread the chip on TL866 I have a new value 🙁

It seems your eprom corrupted but maybe there is a way to read it.Just lower the VCC and VPP slightly.You need to lift VCC(Pin28) and VPP(Pin1) pins from TL866 and feed the chip with lower voltages with external adjustable power supply for example if chip operating voltage is 5.0 volts start with 4.5 volt.(Also disable "pin detect" on programmer since we are feeding chip externally it will complain about pins. )

In that case, there is still enough trapped charge to turn on the transistors. You can tell if you are reading the chip reliably by reading it multiple times. If you always get the same data, then probably you are getting the correct data.

27c256 chips are +7.0v and -0.6v tolerant measure your board Bios sockets pin 28 and 1 with removed chips.I believe you will likely get 5v for VCC and 5 or 12v for VPP.Lets say you get 5 v lower the voltage as described above.

Don't take my advice as "professional".

Shall i send you a copy of mine?
And btw thanks for the information!

Thanks for the advice, I try this method, but it seems complicated for me.
I reread the bios chip with many possible values, with disabled check id, and calculate md5 sum for dumps, every time I got a new hash.

LeFlash wrote on 2021-03-24, 13:48:

Shall i send you a copy of mine?
And btw thanks for the information!

Attach your BIOS dump in the forum thread for history 😀

Here we go!

Ok here is what i mean.It is not complicated come on 😀

"with disabled check id" or another parameter will not help in your case.
Red and black wires are going to external adjustable power supply.Of course my chip is 32 pin you have to adapt to 28 pin.
Since bios is already shared by "Le Flash" not needed to do but maybe you can try for educational pruposes or just keep in mind.

LeFlash wrote on 2021-03-24, 14:30:

Here we go!

Thanks a lot!
BIOS date in this dumps 08/15/89, but in my seems newer 04/30/91.
Maybe I try the method with an external power supply to get dump from U79 😀

Just a little update, a read U79 on another programmer (older, but more professional) from my friend, and I hope the BIOS dump is correct.

Hi all,

Bumping this thread - I got this Intel 386 motherboard which is quite similar to the one above but not not entirely. The board above seems to have an integrated chipset while this one has a lot of smaller chips. Can anyone identify it?

Mostly it works fine but I'm having some issues with the memory. It only gives me 512 KiB conventional memory. There is a BIOS setting to enable 640 KiB but it doesn't work and instead an error is thrown at boot. Disabling ROM shadowing makes no difference either.

I believe I'm using parity SIMMs (the modules have 3 chips: Two 1M x 4 chips and an additional 1M x 1 chip).

• With 4 SIMMs in I get 512 KiB conventional and 3072 KiB extended.
• With 8 SIMMs in I get 512 KiB conventional and 7168 KiB extended.

Either way it seems 512 KiB is just missing? Any hints are appreciated. 😀

bump
II have a similar motherboard too - SBC386At25F04, manual missing. But that's not the main problem with it. The mainboard powers up, but the keyboard LEDs are flashing continuously and it seems to be running like in slow motion - I had to wait about half minute until the speaker began to beep signalizing Keyboard Controller Error (that is 3-2-4 sloooow beeps). There's also no video signal. I guess replacing the controller could solve one of these problems- am I right? And if so, where is it located on the mobo? (I've identified a serial controller, interrupt controller, DMA controller, programmable timer, and bus transceiver so far)