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386 SBC by Alexandru Groza
https://oldcomp.cz/viewtopic.php?f=57&t=9219
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Autor:  Александр [ 30.08.2021, 17:50 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

OK, thanks for the answer.

Autor:  Александр [ 30.08.2021, 19:14 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Obrázek

Current state of the project vs previous built xi8088.

Autor:  Marty [ 31.08.2021, 21:30 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Same here, I did not find one yet. However I was in touch with somebody that perhaps knew of some replacement, so I will definitely let you know here if something relevant is found. :)

Autor:  Александр [ 03.09.2021, 17:33 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Martin8bity píše:
Mně to chodí ;)


May you please share workable bios image? My colleague already soldered the board, but it is not started and no postcodes showed.

Obrázek Obrázek Obrázek

Autor:  Martin8bity [ 04.09.2021, 17:30 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Александр píše:
May you please share workable bios image?

Send me your e-mail to PM.

Autor:  Александр [ 05.09.2021, 21:57 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Looks I found an analog of rft vqb37 on ebay, but it here is too expensive as for me.
https://www.ebay.com/itm/283974850597

Autor:  Александр [ 14.09.2021, 11:11 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Obrázek

Let's start.

Autor:  Александр [ 20.09.2021, 17:09 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

We have found an issue. Resistance of R19 have to be 22Ohm, to provide 0.4 V of logical zero. Currently it provided 1.5V, and it is out of TTL specs. Please make this change, in case if no reset button functionality.

Autor:  Martin8bity [ 21.09.2021, 10:23 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Александр píše:
We have found an issue. Resistance of R19 have to be 22Ohm, to provide 0.4 V of logical zero. Currently it provided 1.5V, and it is out of TTL specs. Please make this change, in case if no reset button functionality.

You are right, I actually replaced it by wire some time ago ;-) It could be better to increase the value of R20 to 1k5. I do not think there is so strong pullup (330R) needed. It would change the reset time constant, but it is quite low, so it should not be a problem. The very low pullup is possibly there to prevent disturbances on the quite long reset wire that goes all over the board to IC24.

Autor:  Александр [ 21.09.2021, 14:02 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Martin8bity píše:
You are right, I actually replaced it by wire some time ago ;-) It could be better to increase the value of R20 to 1k5. I do not think there is so strong pullup (330R) needed. It would change the reset time constant, but it is quite low, so it should not be a problem. The very low pullup is possibly there to prevent disturbances on the quite long reset wire that goes all over the board to IC24.


It is looks also acceptable, I wanted to keep the delay of reset signal, and 22 ohm resistor will not provide any significant overcurrents to reset switch.

Also below the current state of my board.

Obrázek

Autor:  Martin8bity [ 21.09.2021, 15:31 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Did your friend got it to work?

Autor:  Александр [ 21.09.2021, 17:37 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

His board not started at all. Clocks looks good, reset and power good signals are present. CPU address lines looks active, but no romcs# signal and seems data lines contained trash.

He changed ic's on known good, rechecked connections between cpu and chipset, swapped chipset with workable one from 486 board, 486 still workable, but the system symptoms has unchanged.

We have no ideas now, except full tracing entire boards connections.

486 board, used for chipset testing:
Obrázek

Autor:  Martin8bity [ 21.09.2021, 18:00 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

By chipset you mean both, the OPTi 82C495XLC and 82C206? If all clocks are OK it has to be some control signal around the chipset. There are plenty, but I am afraid you will not move without checking everything.

Autor:  Александр [ 21.09.2021, 18:06 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

Currently he checked mostly 82c495xlc and neighbors, 82c206 was swapped with another one, but not completely checked yet, including connections between both ic's.

Autor:  Martin8bity [ 22.09.2021, 12:34 ]
Předmět příspěvku:  Re: 386 SBC by Alexandru Groza

486DLC on 40 MHz seems to be working great. It looks like maybe even better than 386DX ;-) I do not know why, but the floppy seems to be working almost OK now.

Přílohy:
Groza386DX_with_486DLC_Martin.jpeg
Groza386DX_with_486DLC_Martin.jpeg [ 232.88 KiB | Zobrazeno 362 krát ]

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