rasz_pl wrote on 2023-11-04, 00:46:
try graphic card in another slot
Done. Still the same.
rasz_pl wrote on 2023-11-04, 00:46:
so you remove Pentium SBC, put 486 SBC in same slot and graphics magically work and PC boots correctly?
Yes, I have two machines with same graphics cards. 486 board works in both of them. Original and replacement Pentium SBCs don't work in either of them.
rasz_pl wrote on 2023-11-04, 00:46:
This is indeed weird, only hypothetical cause I can come up with right now for something like this would be: graphic card/backplane somehow failing to work in full 16bit mode, Pentium requiring full 16bit ISA, 486 tolerating 8bit?
Maybe, I'm not sure. Only way to tell is get another, more simple grahpics card. Attached is picture of current graphics card. For reference, it's Scorpion machine vision card (that's all I know). The top VGA connector is used for the monitor, the middle VGA connector is for two camera inputs (I think) and the bottom BNC connector is used for another camera where you can overlay video on to the PC screen, so it basically mixes the camera input which graphics output.
rasz_pl wrote on 2023-11-04, 00:46:
Definitely try another ordinary ISA graphic card, you can also try PCI VGA since Pentium SBC supports PCI bus.
I will just have a look on Ebay UK but I'm not really sure what to look for. I'll check it out and maybe post some links later? Not sure if I select a random old graphics card on Ebay it might be too new & not work.
rasz_pl wrote on 2023-11-04, 00:46:
Yeah, its very unlikely at this point that the problem was in RTC, unless there is some special BIOS setting required to make the ISA card work correctly and empty battery erased CMOS settings? But how would one get to that bios setting in the first place? and that wouldnt explain two motherboards doing same thing, did you mess with RTC of the second SBC right after receiving it and before trying it out?
No, I did not remove RTC from replacement Pentium SBC before trying it, it was DOA. I know that if I leave the RTC unplugged from the SBC, it does nothing, no beeps just dead. To me., this indicates that even with failing RTC it is probably trying to boot.
What backs this theory up a little is that if I put in an old RTC into the 486 board it give a "CMOS battery low" message at boot but you can still get in to BIOS etc etc.
rasz_pl wrote on 2023-11-04, 00:46:
Maybe SBC clocks ISA bus too fast out of the box? Maybe it will boot with this special ISA graphic card and ordinary PC PCI VGA simultaneously?
Not sure about this. Maybe. Only way to tell is try another graphics card I guess.
rasz_pl wrote on 2023-11-04, 00:46:
Maybe CMOS SRAM contains some secret magic key required to properly initialize this proprietary special graphic card?
Could be, but I don't think so. The reason is that the 486 SBC needs settings changed in the BIOS to work for this grapghics card, not for the VGA output but for the "frame grabber" functions. I know this, because when removing known good RTC module from working 486 board the BIOS forgot all the settings and I had to change them back. Even with the graphics card not working properly, you can still see VGA output, get can then get into the BIOS and make the changes which allow the "frame grabber" function to work. I was told by an technician who used to work on these machines, that the BIOS changes you need to make are this:
BIOS “Advanced Setup” you need to have:
Adaptor Shadow Cacheable DISABLED
System BIOS Shadow Cacheable DISABLED
ISA Video ROM C000,32K ABSENT
In Chipset Setup :
VGA farme buffer size DISABLED
All IRQ’s set to ISA
VGA Pallette Snoop DISABLED
I had no idea what any of the above means, but I found similar things in the BIOS of the 486 board, changed them and it started working again. Note; I only had to make those changes because I pulled out the known working RTC module from the 486 board to try it in the faulty Pentium SBCs.
rasz_pl wrote on 2023-11-04, 00:46:
Did your 486 SBC come from same machine originally? Can this be some secret sauce cloning protection/software license key thing?
The 486 board came from a spare PC which I bought and now using as a test bed. It has all the same cards as my machine. PCs are identical. I don't think any security stuff is installed on it, the reason being that the software was written for this machine and the application is so niche. Basically you need one of these machines for the software to be any use. It's all running on DOS, not Windows. We are talking 1993 / 1994 vintage.
rasz_pl wrote on 2023-11-04, 00:46:
You could try backing up CMOS ram in 486 board, unplugging RTC chip on live system, plugging one of your spare modules in, loading settings back in, swapping it back to Pentium system and trying to boot that.
Not sure how to do that! I am a little hesitant to mess with the working 486 card again too much, since my machine currently depends on it. After all, by simply unplugging the good RTC from there I was able to make it forget the correct grahpics card settings for the video inputs. My preferred route would be to try and diagnose & fix these two Pentium boards if I can, whilst leaving the working machine alone.
rasz_pl wrote on 2023-11-04, 00:46:
Your 486 box has second special graphic card or are you reusing the same one?
I have two graphics cards both the same. One is in working machine, other installed in space PC.
Venture wrote on 2023-11-03, 20:29:
I'm in the UK. I will get one of these post cards ASAP.
rasz_pl wrote on 2023-11-04, 00:46:
I think it will just say Graphic card init fail like the beeps, but its cheap enough to be worth having anyway
I had a look around for the Post card and Amazon can deliver late next week. Ebay is the same so it'll be a few days before we can test.
rasz_pl wrote on 2023-11-04, 00:46:
CY7C199 is SRAM so that should be cache. I dont know why there are 6 chips, weird number for cache. Replacing 12ns cache SRAM with 20ns definitely has potential to stop the board from booting completely, except if it was Cache bios should still have chance to beep error codes. The one ebay $4500 listing for that SBC has all 8 soldered in, picture quality is terrible, but it almost looks like -15 version chips.
You're right. Originally the board has 8 RAM chips on it. When I took the photo I had already desoldered two! Initially my idea was to desolder one at a time, swapping it for one on the other Pentium board just in case one faulty RAM IC was bringing the whole SBC down. I quickly got bored of that idea and went for the option of buying the slower RAM chips on Ebay and installing them, also a shitty idea. For reference, the board behaved the same with 8 RAM chips, 6 RAM chips or zero RAM chips, I tried a few different things! 😀
If you found the Ebay listing then you must've fallen off your chair like I did. How crazy is it that someone can try to charge $4500 for a "maybe working" board with zero warranty, I think that's outrageous. I know there maybe someone in the world who needs a machine in a factory somewhere to get working again ASAP but it's a huge risk to take, especially as the SBCs used in there are somewhat generic.