VOGONS


First post, by whitepawn

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Hi,

I couldn't help myself and bought another single board computer which labeled as PC420-G2 by protech company. Here is SBC page in 1997:
https://web.archive.org/web/19970327052802/ht … .tw/ipc420.html

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After cleaning the board, installed another cpu Cx486 dx2 66 (because the one came with the board is not original, socket was very loose) it posted with "Bios checksum error".I searched online for this error it seemed either bios rom is corrupted or RTC battery problem.Second one is easy to fix for me so i retrofitted CR2032 to dallas chip but checksum error persisted so i tried another bios ( PSC-486 VER:C Jumper or manual information needed) with it which has same chipset and even bios stickers are the same. Also PSC-486 bios gives same error which i believe i have a jumper setting problem.(Top left bios is similiar bios from my working PSC-486.Bottom right is original bios.)

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I can boot from A: drive and tried uniflash but bios chip model seems unknown in uniflash.

Started looking for bios backups online but couldn't find any.Meanwhile i discovered same hardware was labeled as "486/586 SBC Ver:GC".This board is very similiar to my board but also i couldn't find any information about it.

By any chance does someone have manual information for it?Or any advice?

Thanks in advance.

Last edited by whitepawn on 2021-03-23, 12:08. Edited 1 time in total.

Reply 1 of 13, by computerguy08

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This being a 486 platform, I'm not sure Uniflash has full support for it (if at all). Furthermore, those BIOS ICs look like UV EPROMS, which need to be erased with a UV lamp, then programmed with a programmer like TL866.
Even if the chip was not UV, I don't think the SBC is able to flash the BIOS chip (probably lacks the Vpp circuitry, I could be wrong though, so not sure).

I'll look around the web and see if I can find more info.

Looking for a motherboard? You can find it in Ultimate Hardware 2019: http://www.win3x.org/uh19/motherboard/search
Join our UH19 Discord server here: https://discord.gg/HWWH7hsk2p

Reply 2 of 13, by whitepawn

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Hi,
Thanks for your reply.
You are absolutely right my bad, i didn't give full information.Let me explain with more details:

As i mentioned i have fully working PSC-486, in this board i backed up bios file with uniflash and hotflashed a spare chip (MX28F1000PPC-12C4) with a socket 7 board (Tomato 5STX) and tested on PSC-486 which works without any issues.Here is my topic quote:PSC-486 VER:C Jumper or manual information needed

whitepawn wrote on 2021-03-09, 20:39:
Hi again, I was able to backup bios with uniflash and tested backed up bios with another bios flash chip.Basicly first i backupe […]
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Hi again,
I was able to backup bios with uniflash and tested backed up bios with another bios flash chip.Basicly first i backuped bios and hotflashed a spare chip with another socket 7 board, then i removed original bios chip and installed hotflashed spare chip. System booted fine so you can trust this bios file.Please add your database for future reference.Here is the bios and cmos backups:
psc486bios.rar
Please add any information if available.

And here is my spare chips(MX tested, Intel one is not tested i plan to use it for PC420-G2)

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Unfortunately i dont have any kind of eeprom programmer to read original eeprom.

Thanks again, please share if you have found any information.

Reply 3 of 13, by whitepawn

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I have done my research and found two similiar boards to mine.
One of them is
"486/5X86 SBC Ver:GC"
And the other one is
"NAGASAKI IPC Embedded Computer, 960420 GCA, 486/5x86 SBC Ver:GC" aka "NASA-PC420" according to archive.org:
https://web.archive.org/web/20000307120159/ht … m.tw/NA-420.htm

Unfortunately none of them are have documentation or bios files but i found a guy who has issue with bios also on another vintage hardware forum.He used HS-4000 bios to work his card.I asked him to share bios file and he shared with me thanks to him.I flashed MX chip via socket 7 mobo with hotflash method.

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Tried on my PSC-486 it posted as HS-4000 and works, i tried same bios chip on my PC420-G2 it shows again "bios checksum error".I am pretty sure i installed correctly jumpers because in this SBC 486 DX4-100 topic he uses ST486DX-100 and i am using AMD486DX-100.If i change jumpers to when i bought condition, only cyrix DX2-66 works.

Since i can boot from floppy i checked uniflash if bios chip recognized correctly ,yes it detects mx chip perfectly.

I also tested my PSC-486 bios with PC420 but still have "bios checksum error".

All this tests are lead me think one thing which is a hardware issue or are there another software in this board?Any theories?

Reply 4 of 13, by whitepawn

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Ok i have done my homework.

Firstly it wasn't a hardware issue.I managed to work board with Intel DX2 66 Mhz.It was a jumper issue and bios issue.Also here is the interesting thing if i boot system with wrong jumper settings it posts but it gives error "bios rom checksum error".Has anyone ever came across case like this?

Here is my DX2 66Mhz jumper settings:

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And here is the bios file that i have used from mt777’s board(486/5x86 SBC ver:g6)Thanks to him, It works fine:

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And here is my excel worksheet to reverse engineer jumper settings.I may update this when i try more cpus:

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And here is my new problem.It conflicts i/o 278:

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I have checked bios settings to disable com port but none of them worked.Maybe it is related to jumpers?Any idea?

Reply 5 of 13, by mt777

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5X86 is not 100% correct jumpers. I found this photo in local auction but it seems that 3x multiplier is set (so as DX4-100). I will try in my board set Am5x86 properly.
Voltage jumper: 1&2 5V, 2&3 = 3.3V ?
278h is lpt secondary port?

In your free time please recheck all SBC manuals and find similar jumper layout. I really believe that something similar exists there but didn't check all of them.
ftp.emacinc.com/LegacyProducts/SBC/

Last edited by mt777 on 2021-03-19, 00:48. Edited 1 time in total.

Reply 6 of 13, by whitepawn

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Oh i see, a test will be useful.

Voltage jumper is:
1-2 closed=3.3v
2-3 closed=3.45 v
all open=3.3v from my board.

No 5v combinations i have found yet.You can confirm via middle leg of voltage regulator and a multimeter before installing cpu.

Reply 8 of 13, by whitepawn

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Yes dx2's are 5v cpu's but works fine with 3.3 volts in my case.

My board have LX8385-00 (which is an adjustable voltage regulator, not fixed) not LT1085 so i expect voltages other than 3.3volts 😀

Could you measure your board 1-2 closed, 2-3 closed and all open if possible?Maybe my board or regutator is faulty.

Reply 9 of 13, by mt777

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I checked VCC directly on PGA168.
JP9. 1&2 = 5.1V, 2&3 = 3.4V, none = 0V
JP4. Tried different configuration and 1&2, 5&6 = gives 120MHz. None success setup as full 133MHz.
So I helped you, hope that you find Am5x86 config 😀

Reply 10 of 13, by whitepawn

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I see, let me check on my board from cpu socket.

About JP4 only 1-2 closed gives 80mhz 1-2 and 3-4 closed seems 66mhz on my board.

Thanks for testing.Since i don't have an AM5x86 i am unable to test it.

Also another info about i/o error i disabled com ports and parallel port no luck.

I have searched many of ftp.emacinc.com/LegacyProducts/SBC/ no similiar jumper setups.

Reply 12 of 13, by whitepawn

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Ok I invested a TL866 Programmer and read original chip then i compared it with my PSC-486 bios.Surprisingly it was very similiar to PSC-486 bios only some of bytes are changed so i decided to flash PSC-486 bios and board is booting fine without i/o conflicts or so.I can boot DOS.

When i was repairing this board i removed cache chips to aviod further troubleshooting.I installed cache chips but now it freezes if i enable external cache.Also diagnostic board says 61/60 which translates "Try to turn on level 2 cache" i checked from diagnostic board manual.Either i have to disable L2 cache or remove second chip then system boots fine.

After some investigation i found JP11 and JP12 backside of board which i believe are jumpers for cache size or enable.Here is detailed photo of it:(It came originally both open)

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I tested chips with TL866 all passed test.Also tested on another 486 board works fine.I have tested only JP11 closed, only JP12 closed and both closed but no luck.

Any ideas?

Reply 13 of 13, by whitepawn

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Ok i figured it out it was a bad solder joint on ALI M1489.I soldered it and cache is detected.Checked with cachechk4:

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Also figured out if you use 32 pin instead of 28 pin JP11 and JP12 must be enabled i believe.So it is not relevant in my case since i only have 28 pin sram.

Here is my simple diagram:

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DOS is not booting with WB (Write Back) only boots with WT mode which my Cyrix 486DX2-66 does not support obviously.Also this was a noob mistake i made 😀

I have checked voltages on directly on PGA socket and yes mt777's results are correct.(JP9. 1&2 = 5.0V, 2&3 = 3.45V, none = 0V)Please ignore my previous posts about it.

I figured out all my bios and cache issues so i can move to improve cpu jumper settings.I will update excel when i finish my work.Any contributions are welcomed.