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My i486 DOS PC Build - Possible Motherboard Fault?
Re: My i486 / Retro PC Build - Your Input Is Wanted!
In all seriousness though, I did have another idea for this empty spot. More or less plug it up with a piece of plastic, but mount a homemade 2 digit turbo display there.
https://www.vogons.org/viewtopic.php?p=970157#p970157
(Pictures in linked thread)
But as cool as a frequency display would be, this case wasn't designed for one and I was afraid it might look shoehorned in that spot.
https://www.vogons.org/viewtopic.php?p=970157#p970157
(Pictures in linked thread)
But as cool as a frequency display would be, this case wasn't designed for one and I was afraid it might look shoehorned in that spot.
Re: My i486 / Retro PC Build - Starting to come together!
I decided that black plate thing is good enough for now. I could always circle back and change it if it bothers me. I was just trying to avoid doing that because to get good access to it I need to remove the front bezel, which means I have to remove the drives and probably unplug all of the front panel connectors. But whatever, it's been long enough, it's time to start putting this thing together!
PSU installed, motherboard installed, and front panel connectors hooked up. Hooking up the front panel connectors is always an early step because it's usually so much harder to do later on. Am I right?
This case requires taller motherboard standoffs than the ones I have. I've only ever had the one size standoffs, which were good for everything. This is the first case that I need taller ones for. Good thing this case came with some installed in it already. I had to drop a few in vinegar to clean them up a little. Very strange though, someone taped a plastic washer to the bottom side of the mobo under one of the mounting holes, and it turns out it's the perfect spacer to use one of the shorter standoffs I have on hand. I was short 1 taller standoff, and there's one spacer already taped onto the mobo to use a shorter one. What a coincidence!
I'm not going to even attempt anything at cable management until after everything is confirmed working. It would be nice to wrangle the cables as I go, but then it would be too much of a pain in the ass to undo everything when I inevitably have to tweak things and troubleshoot.
Case in point:
I was able to line up 6 mounting holes, and I got them all screwed down to the standoffs. Then when I went to put some ISA cards in, they wouldn't fit! In the above pic, you can see how the mounting bracket is up against the case, but the edge connector of the card doesn't line up with the ISA slot. What the fuck!?
So what I did was remove all 6 mounting screws. Then with the mobo just floating on top of the standoffs, I installed a card in the first and last ISA slot to get it in position and squared up. The mobo is now where it has to be so that the expansion cards fit, but now this is how the mounting holes line up...
You can see the brass standoff, the mounting hole on the motherboard is half overlapping it! I thought maybe the case was bent out of shape, but no. So I did a Google search and found a thread on Vogons where a few people said they've had issues with AT mobos not lining up correctly. So I guess this is just a quirk of AT that I'll have to deal with.
So I think I came up with an easy fix for this: Wood. I will measure the height of the standoffs, then I will cut a piece of wood to that thickness, then cut it into little squares or whatever. Then I will lay them on the bottom of the case, approx where they need to be, and screw them on from the underside of the case. Then I'll lay the mobo in there, and install a couple of ISA cards to make sure it's all lined up correctly. Then I will use wood screws through the mobo's mounting holes into the blocks of wood.
Wood isn't conductive, so I don't have to worry about that. But then you might say that now the mobo wont be grounded to the case. But it definitely still will, the ISA card brackets and the PSU are ground points to the case. And some AT motherboards were mounted with those (awful) plastic clips, and those definitely aren't grounded, so I don't see this being a problem.
I can't drill and tap new mounting holes in the case, because the mounting holes are half overlapping the existing holes. So that being the case, I think my wood blocks idea is a good solution. It's simple and easy enough to do. It will definitely hold the mobo tightly to the case. I will have PERFECT alignment. You wont ever see the wood blocks once the mobo is installed. I see no down side to it.
PSU installed, motherboard installed, and front panel connectors hooked up. Hooking up the front panel connectors is always an early step because it's usually so much harder to do later on. Am I right?
This case requires taller motherboard standoffs than the ones I have. I've only ever had the one size standoffs, which were good for everything. This is the first case that I need taller ones for. Good thing this case came with some installed in it already. I had to drop a few in vinegar to clean them up a little. Very strange though, someone taped a plastic washer to the bottom side of the mobo under one of the mounting holes, and it turns out it's the perfect spacer to use one of the shorter standoffs I have on hand. I was short 1 taller standoff, and there's one spacer already taped onto the mobo to use a shorter one. What a coincidence!
I'm not going to even attempt anything at cable management until after everything is confirmed working. It would be nice to wrangle the cables as I go, but then it would be too much of a pain in the ass to undo everything when I inevitably have to tweak things and troubleshoot.
Case in point:
I was able to line up 6 mounting holes, and I got them all screwed down to the standoffs. Then when I went to put some ISA cards in, they wouldn't fit! In the above pic, you can see how the mounting bracket is up against the case, but the edge connector of the card doesn't line up with the ISA slot. What the fuck!?
So what I did was remove all 6 mounting screws. Then with the mobo just floating on top of the standoffs, I installed a card in the first and last ISA slot to get it in position and squared up. The mobo is now where it has to be so that the expansion cards fit, but now this is how the mounting holes line up...
You can see the brass standoff, the mounting hole on the motherboard is half overlapping it! I thought maybe the case was bent out of shape, but no. So I did a Google search and found a thread on Vogons where a few people said they've had issues with AT mobos not lining up correctly. So I guess this is just a quirk of AT that I'll have to deal with.
So I think I came up with an easy fix for this: Wood. I will measure the height of the standoffs, then I will cut a piece of wood to that thickness, then cut it into little squares or whatever. Then I will lay them on the bottom of the case, approx where they need to be, and screw them on from the underside of the case. Then I'll lay the mobo in there, and install a couple of ISA cards to make sure it's all lined up correctly. Then I will use wood screws through the mobo's mounting holes into the blocks of wood.
Wood isn't conductive, so I don't have to worry about that. But then you might say that now the mobo wont be grounded to the case. But it definitely still will, the ISA card brackets and the PSU are ground points to the case. And some AT motherboards were mounted with those (awful) plastic clips, and those definitely aren't grounded, so I don't see this being a problem.
I can't drill and tap new mounting holes in the case, because the mounting holes are half overlapping the existing holes. So that being the case, I think my wood blocks idea is a good solution. It's simple and easy enough to do. It will definitely hold the mobo tightly to the case. I will have PERFECT alignment. You wont ever see the wood blocks once the mobo is installed. I see no down side to it.
Re: My i486 / Retro PC Build - Starting to come together!
Just for my own sanity, I decided to test this case with another baby AT board. I installed my DTK socket 7 board in this case, using 6 standoffs, and it fit perfectly, and I'm able to insert a PCI card without issue! So it's not the case, the mounting holes on the PC Chips socket 3 board are definitely off. 
My wood idea can still fix the issue, but I forgot about one thing that made it go from easy as pie to slightly annoying. I was thinking I could just cut blocks of wood, almost arbitrary in size, as long as the thickness was the same height as the standoffs. And then screw in the mobo using it's mounting holes. But make the blocks big enough so that when I put screws into them from the bottom of the case, the locations are off set from the screws that'll mount the mobo. Because the wood isn't thick enough, if those screws are in the same position they will hit I think. The problem here though is that the mobo can't play flat on the block of wood due to through hole components protruding on the bottom side of the board. So in short, this idea went from having a large margin of error for mounting the blocks (easy) to having a much small margin of error (not as easy). Maybe I could try using shorter screws, but I don't think this is possible.
And I really don't want to mod the case to fit this PC Chips board. If the board is the problem, I don't want to permanently alter the case. For example, if this mobo ever dies I'd like to swap in a replacement, which wouldn't be possible if I modify the mounting hole locations. So, yeah, I'll have to come up with something.
Or, get another motherboard!
I was thinking, this may be the easiest solution... On the expansion slot side of the board, once I have a few cards installed and screwed into the case, those are really going to hold the mobo down on that side. Then on the other side of the mobo, the side facing the front of the case, there's two holes in each corner that aren't typically used (they don't line up with any mounting holes in the case). I could put the board in, install all my expansion cards, then mark the location of those two aforementioned holes. Then drill/tap holes for standoffs. So in short, one side will be held down by the expansion cards, and the other side will have two screws. That would be more than enough to securely hold the mobo in the case. I would just have to be sure to use one hand to hold the mobo down whenever removing an expansion card.
But first, I will look on eBay and see if there's any cheap socket 3 motherboards I can pick up. (sorta joking, but not really)
edit: After some playing around with it, I was able to install 4 ISA cards and managed to get one screw into a standoff located in the center of the board. That seemed to be secure (plugging/unplugging the keyboard, etc). The only thing is, everything seemed to be under a lot of tension. So I'm not sure how wise it would be to keep it this way.
edit: I keep forgetting that I have a 3D printer. I found a couple of different standoffs/mounts for PCBs and motherboards. I might be able to make one of them work. Or maybe make one myself, since simple shapes aren't too difficult to make in Tinkercad.
My wood idea can still fix the issue, but I forgot about one thing that made it go from easy as pie to slightly annoying. I was thinking I could just cut blocks of wood, almost arbitrary in size, as long as the thickness was the same height as the standoffs. And then screw in the mobo using it's mounting holes. But make the blocks big enough so that when I put screws into them from the bottom of the case, the locations are off set from the screws that'll mount the mobo. Because the wood isn't thick enough, if those screws are in the same position they will hit I think. The problem here though is that the mobo can't play flat on the block of wood due to through hole components protruding on the bottom side of the board. So in short, this idea went from having a large margin of error for mounting the blocks (easy) to having a much small margin of error (not as easy). Maybe I could try using shorter screws, but I don't think this is possible.
And I really don't want to mod the case to fit this PC Chips board. If the board is the problem, I don't want to permanently alter the case. For example, if this mobo ever dies I'd like to swap in a replacement, which wouldn't be possible if I modify the mounting hole locations. So, yeah, I'll have to come up with something.
Or, get another motherboard!
I was thinking, this may be the easiest solution... On the expansion slot side of the board, once I have a few cards installed and screwed into the case, those are really going to hold the mobo down on that side. Then on the other side of the mobo, the side facing the front of the case, there's two holes in each corner that aren't typically used (they don't line up with any mounting holes in the case). I could put the board in, install all my expansion cards, then mark the location of those two aforementioned holes. Then drill/tap holes for standoffs. So in short, one side will be held down by the expansion cards, and the other side will have two screws. That would be more than enough to securely hold the mobo in the case. I would just have to be sure to use one hand to hold the mobo down whenever removing an expansion card.
But first, I will look on eBay and see if there's any cheap socket 3 motherboards I can pick up. (sorta joking, but not really)
edit: After some playing around with it, I was able to install 4 ISA cards and managed to get one screw into a standoff located in the center of the board. That seemed to be secure (plugging/unplugging the keyboard, etc). The only thing is, everything seemed to be under a lot of tension. So I'm not sure how wise it would be to keep it this way.
edit: I keep forgetting that I have a 3D printer.
I found a couple of different standoffs/mounts for PCBs and motherboards. I might be able to make one of them work. Or maybe make one myself, since simple shapes aren't too difficult to make in Tinkercad.Re: My i486 / Retro PC Build - Starting to come together!
I ended up making my own mounting standoffs / bracket things in Tinkercad and test printed a few last night.
Just a simple right-angle standoff with a 10mm height. I was able to find similar ones on Amazon, but they were all like 20mm tall. So I copied that basic design and made my own that are 10mm tall. I made it so that the hole on the square part can somewhat loosely fit a 6x32 screw, but the hole on the top can have a 6x32 thread into it. I threaded one screw in with just a typical PC screw, and it's doable, but takes a lot of effort to cut the threads. Luckily, I have a tap and die set on hand to make this easier.
I printed 6 more brackets and used a tap to cut threads into them.
Just a shot of the standoffs on the underside of the motherboard.
(In case anyone missed the problem in a previous post) The reason for the offset mounting hole is that this stupid motherboard doesn't line up correctly with the mounting holes in the case. They are close though, and half overlapping each other, so I cannot simply drill and tap new holes for standoffs. Thus the offset bracket.
But how do I mark the location of the new holes to drill? That might be a challenge!
I've come up with a few ideas for that. For starters, The post hole that's threaded for 6x32, I made that hole go all the way through the piece (even though the screw is not nearly that long). This is so I can align it without a screw in there, and possible mark a location. For example, if I take a thin dowel or something and put some ink or whatever on one end, then play Operation and plunge it through the motherboard's mounting hole and straight through the bracket and mark a location on the case. Then lift the mobo out, like the bracket up with that marked hole and then see exactly where I need to drill the new hole. Easier said then done, though, especially since the holes are overlapping.
There's two holes on the other side of the mobo, the side facing the front of the case. I don't believe they are intended to use for mounting the mobo inside a case, I think they might be there for manufacturing. But I think I can use them. There are traces very close to these holes though, and no "stay clear" or ground ring for a screw, so I have to be careful. If I tighten down a metal screw, that might damage a trace. So for now I will be careful, but I think ultimately I will use a plastic screw here.
Anyway, I altered the bracket so that it has an angled offset...
It will become clear why by looking at them in the next pic...
If I used the first right-angle bracket, that would put the new mounting hole in an awkward position. The bottom of the case is stamped in such a way that you can thread in the standoff posts and the threads wont scratch your desktop. You can see in this above pic, those "mounting" holes on the mobo are off the stamped portion of the case. Also, the one next to the drive cage, it would be hard to drill a hole that close to the cage.
And you can see in this new offset bracket thing that the hole for mounting it to the case is now oblong. I figured using an oblong hole for this screw will allow for a margin of error when I mark the locations for them. So just in case I'm off slightly when I drill the new holes, I can (hopefully) still make it work. So I decided to reprint the 6 regular standoffs, now with oblong mounting holes.
Just a simple right-angle standoff with a 10mm height. I was able to find similar ones on Amazon, but they were all like 20mm tall. So I copied that basic design and made my own that are 10mm tall. I made it so that the hole on the square part can somewhat loosely fit a 6x32 screw, but the hole on the top can have a 6x32 thread into it. I threaded one screw in with just a typical PC screw, and it's doable, but takes a lot of effort to cut the threads. Luckily, I have a tap and die set on hand to make this easier.
I printed 6 more brackets and used a tap to cut threads into them.
Just a shot of the standoffs on the underside of the motherboard.
(In case anyone missed the problem in a previous post) The reason for the offset mounting hole is that this stupid motherboard doesn't line up correctly with the mounting holes in the case. They are close though, and half overlapping each other, so I cannot simply drill and tap new holes for standoffs. Thus the offset bracket.
But how do I mark the location of the new holes to drill? That might be a challenge!
I've come up with a few ideas for that. For starters, The post hole that's threaded for 6x32, I made that hole go all the way through the piece (even though the screw is not nearly that long). This is so I can align it without a screw in there, and possible mark a location. For example, if I take a thin dowel or something and put some ink or whatever on one end, then play Operation and plunge it through the motherboard's mounting hole and straight through the bracket and mark a location on the case. Then lift the mobo out, like the bracket up with that marked hole and then see exactly where I need to drill the new hole. Easier said then done, though, especially since the holes are overlapping.
There's two holes on the other side of the mobo, the side facing the front of the case. I don't believe they are intended to use for mounting the mobo inside a case, I think they might be there for manufacturing. But I think I can use them. There are traces very close to these holes though, and no "stay clear" or ground ring for a screw, so I have to be careful. If I tighten down a metal screw, that might damage a trace. So for now I will be careful, but I think ultimately I will use a plastic screw here.
Anyway, I altered the bracket so that it has an angled offset...
It will become clear why by looking at them in the next pic...
If I used the first right-angle bracket, that would put the new mounting hole in an awkward position. The bottom of the case is stamped in such a way that you can thread in the standoff posts and the threads wont scratch your desktop. You can see in this above pic, those "mounting" holes on the mobo are off the stamped portion of the case. Also, the one next to the drive cage, it would be hard to drill a hole that close to the cage.
And you can see in this new offset bracket thing that the hole for mounting it to the case is now oblong. I figured using an oblong hole for this screw will allow for a margin of error when I mark the locations for them. So just in case I'm off slightly when I drill the new holes, I can (hopefully) still make it work. So I decided to reprint the 6 regular standoffs, now with oblong mounting holes.
Re: My i486 DOS PC Build - Mounting Motherboard Mayhem!
So those two angled offset brackets that I made worked out great. I drilled and tapped the holes in the case, and they are securing the mobo well enough. I'm using the other plastic standoffs I made just as spacers, but the two in this below picture are the only two that are actually screwed into the case. With all of the ISA cards installed on the other side, which are screwed in, the mobo is held down nicely. I decided to leave well enough alone.
Got the external drives installed. I was gonna put the CD-ROM on top, but as it turns out that 3.5" floppy spacer thing doesn't fit any where else put the top slot.
Because imgur changed stuff, the last picture I posted of my controller card is no longer uploaded. So here it is (again)...
And here's the sound card I'm gonna go with (for now). It's a SoundBlaster 16 CT1740.
I was almost gonna go with a Vibra 16 that I have, which has a real OPL chip and wave table header, but I decided to stick with the OG SB16 for now. Mine has the hanging note bug, but I decided on a different MPU-401 solution. I will eventually be adding a second sound card (hopefully setting both of them up together wont be too much of a pain) that has a much better MPU-401 implementation. But more on that later, when I get that second card.
This is how it's currently looking. But it's far from done. I want to eventually get the CF card reader all the way to the left side, so that it's easier to reach around and eject/insert the CF card. But the current PATA cable I'm using isn't long enough. I think I just need a 6" extension and I'll be all set. But yeah, I'll probably change around the order of the cards to try and find the best fit once I get the second sound card in. Except for the video card, that will remain always in that slot (the one closest to the CPU, due to issues that VLB can have).
Took a quick current reading of the +5V lines to the mainboard and got about 3A. Of course, this is the system at idle on the post screen and doesn't include the drives. Still, I don't see this being an issue. You might notice that it's reading a negative number on a DC current setting. I actually have no idea what the means. I did a quick Google but didn't find anything solid. I'll have to research this more later.
So I got a complete system installed in the case for the first time, and... I can't boot from the floppy drive. It just hangs there, with the floppy LED staying solid indefinitely. After spending so long refinishing the case and then dealing with the mobo mounting issue, this is a real bummer! I spent enough time dealing with mounting the motherboard, and I was just in no mood to deal with another issue.
Got the external drives installed. I was gonna put the CD-ROM on top, but as it turns out that 3.5" floppy spacer thing doesn't fit any where else put the top slot.
Because imgur changed stuff, the last picture I posted of my controller card is no longer uploaded. So here it is (again)...
And here's the sound card I'm gonna go with (for now). It's a SoundBlaster 16 CT1740.
I was almost gonna go with a Vibra 16 that I have, which has a real OPL chip and wave table header, but I decided to stick with the OG SB16 for now. Mine has the hanging note bug, but I decided on a different MPU-401 solution. I will eventually be adding a second sound card (hopefully setting both of them up together wont be too much of a pain) that has a much better MPU-401 implementation. But more on that later, when I get that second card.
This is how it's currently looking. But it's far from done. I want to eventually get the CF card reader all the way to the left side, so that it's easier to reach around and eject/insert the CF card. But the current PATA cable I'm using isn't long enough. I think I just need a 6" extension and I'll be all set. But yeah, I'll probably change around the order of the cards to try and find the best fit once I get the second sound card in. Except for the video card, that will remain always in that slot (the one closest to the CPU, due to issues that VLB can have).
Took a quick current reading of the +5V lines to the mainboard and got about 3A. Of course, this is the system at idle on the post screen and doesn't include the drives. Still, I don't see this being an issue. You might notice that it's reading a negative number on a DC current setting. I actually have no idea what the means. I did a quick Google but didn't find anything solid. I'll have to research this more later.
So I got a complete system installed in the case for the first time, and... I can't boot from the floppy drive. It just hangs there, with the floppy LED staying solid indefinitely. After spending so long refinishing the case and then dealing with the mobo mounting issue, this is a real bummer!
I spent enough time dealing with mounting the motherboard, and I was just in no mood to deal with another issue.
Re: My i486 DOS PC Build - Freezing Reading Floppy :(
What are the little stand-off mounts made of? Strong enough to hold the pcb?
Re: My i486 DOS PC Build - Freezing Reading Floppy :(
PLA, the typical filament used for 3D printing. I think they're strong enough. I was able to torque a screw down pretty tight and they showed no sign of breaking. Still, I could have made the infill 100% and they'd be even stronger.
Re: My i486 DOS PC Build - Possible Motherboard Fault?
Just to give a little update on the state of this build...
So aside from the annoying mounting issues with the motherboard, once I got it all together and was actually able to use the damn thing, I discovered a show stopper. The motherboard will not boot from any drives!
Anyone have any troubleshooting advice, I'm all ears!
The computer will POST and everything seems normal. It displays the correct amount of RAM, cache, CPU, yada yada. But it hangs when booting from a drive. I've stripped everything out except for the bare necessities. So just the motherboard, CPU, RAM, video card and controller card. If I have no floppy in the drive, it'll report the typical no boot disk and press any key message like normal. If I leave the drive empty and hit a key, it displays the message again like it normally would. But if I put a disk in and hit a key, the FDD will click once and that's it. The floppy light comes on and stays on. There's a blinking cursor on the screen still, but ctrl+alt+del doesn't restart so it's hung there.
I have DOS 6.22 installed on a CF card, and I've been using that between other computers with no issue, but I cannot get it to boot on this motherboard. One reason is because this motherboard will not auto detect the drive, and I don't know the drive parameters. And I cannot load software from floppy to get the drive parameters. I was able to view them on another PC, and I input those specs into the BIOS on this 486 motherboard. I think I got it right, but this was a week or two ago so I don't quite remember what I did. The best result that I got was that it started to load DOS from the CF card but it said "suarting DOS" instead of "starting DOS" (replaced the T with a U) and hung there. The CF card isn't corrupt or anything, I've used it several times since then. Haven't seen that before.
Things I've tried...
- Removed and reinstalled everything at least once
- Tried a different, better, and known-working power supply
- Swapped RAM sticks out, tried different combos including just one at a time
- Swapped the DX2-66 for a DX2-50 that I have on hand, adjusted jumpers accordingly
- Double checked all jumper settings
- Disabled L1 and/or L2 cache in the BIOS (separately and together)
- Changed L1 cache from write-through to write-back (with and without L2 disabled)
- Reloaded default BIOS settings
- Checked controller card on a different motherboard and it works fine booting a floppy
So at this point, I'm starting to think it might be likely a fault with the motherboard. Which would be a real shame! The only reason I started this 486 build was because I was able to get this motherboard at a decent price. I've looked at other 486 boards on eBay a few times over the last couple of weeks, and there's definitely nothing for a reasonable price.
I don't know if I ever mentioned in this thread, but this motherboard is warped pretty good. I could try and reflow the legs of the QFP chips, but, ugh. I don't have a microscope, so I can't examine the board well enough for cracked solder joints.
Putzing around with these old computers is something I do from time to time as a stress reliever. It takes no mental effort on my part, and whatever results are of no real consequence. A couple of years ago I was even willing to mess around with motherboard repair. But for right now, I'm just too short on time and energy for this kind of thing. And I'm kinda bummed that I wasted a couple of hours today troubleshooting this motherboard. And I have to consider that it might have a fault that isn't repairable. So I've been considering my options with this.
I may troubleshoot this a little more, especially if anyone has any suggestions. And I may post on the Vogons forums for help with it. But I'm not sure how much more time I'm willing to sink into it. So that said, I've been considering my options. And here's one I've come up with...
Swap the motherboard for another AT board that I already own.
The thing that sucks about that is that this is the only 486 board that I own. So swapping motherboards kinda kills one of the biggest purpose for this build: To use the legendary DX2-66. After thinking about it some, it still would be a DOS AT build, it would just be a different CPU. Would I really even notice or care after a while? Still, part of it was just to smile at the fact that I was using the quintessential 486 CPU. LOL good thing I decided against getting that DX2-66 case badge!
So I have the DTK Socket 7 board (picture here) that I could use. It's actually a really nice board. It's still AT, so it can fit in the same case. And in a lot of ways it's a better board. I mean, aside from the obvious of the better CPU socket. It has PCI slots, on board I/O controller, USB, and a header for a PS/2 mouse (which would be better than using a serial mouse). I mean, externally you wouldn't even be able to tell a difference. So does it really matter?
One thing that sucks about this route though is that the DTK board has PCI slots but no VLB. I went out of my way to pick up that VLB video card, and although I got a good deal on one it still wasn't cheap. I have zero use for it outside of the 486 board. So that kinda sucks. On the flip side, if I use the DTK board with a PCI video card then I never really have to worry about any performance issues.
And speaking of performance... The DX2-66 could be slowed down with the turbo button, to 33 Mhz I guess is what it does. But to be honest, there really aren't any games I'm interested in that are speed sensitive. And even if that changes in the future, there are other ways to deal with it. So I'm not worried about it. The DTK board doesn't have any turbo function, but it does have a header for a turbo LED. Apparently this was a thing LOL. From what I'm reading, it literally just lights up the turbo LED and has no other point to it.
In regards to the CPU that I would use with the DTK board, right now I have an AMD K5 75 MHz installed on it. From what I'm reading, it's about on par with a similarly clocked Pentium. That combined with a PCI video card means that I'll have a better performing computer overall. And I'm probably better off because I'm in better shape with backup stuff if anything fails. Like the VLB video card, I would be screwed with the 486 build if that card ever died. But a PCI video card, I already have backups and even still they are cheap and plentiful on eBay compared to VLB cards.
So I don't know, I think I'm gonna go with the DTK board for now. It'll still be a dedicated DOS 6.22 computer. It's just a shame that it wont be a DX2-66.
And this thread title will have to change.
And this doesn't mean that I'm giving up on the 486. I can always troubleshoot the stupid PC Chips board more, if and when I have the time or am feeling up to it. And I still could be on the lookout for a 486 motherbaord that doesn't cost an arm and a leg. Although at this point, if I were going to get another 486 board I would want to try and trade up. And all the while I could be enjoying this PC actually working with the DTK board. Should I ever fix the 486 board or get another one, I could always swap it in.
So aside from the annoying mounting issues with the motherboard, once I got it all together and was actually able to use the damn thing, I discovered a show stopper. The motherboard will not boot from any drives!
Anyone have any troubleshooting advice, I'm all ears!
The computer will POST and everything seems normal. It displays the correct amount of RAM, cache, CPU, yada yada. But it hangs when booting from a drive. I've stripped everything out except for the bare necessities. So just the motherboard, CPU, RAM, video card and controller card. If I have no floppy in the drive, it'll report the typical no boot disk and press any key message like normal. If I leave the drive empty and hit a key, it displays the message again like it normally would. But if I put a disk in and hit a key, the FDD will click once and that's it. The floppy light comes on and stays on. There's a blinking cursor on the screen still, but ctrl+alt+del doesn't restart so it's hung there.
I have DOS 6.22 installed on a CF card, and I've been using that between other computers with no issue, but I cannot get it to boot on this motherboard. One reason is because this motherboard will not auto detect the drive, and I don't know the drive parameters. And I cannot load software from floppy to get the drive parameters. I was able to view them on another PC, and I input those specs into the BIOS on this 486 motherboard. I think I got it right, but this was a week or two ago so I don't quite remember what I did. The best result that I got was that it started to load DOS from the CF card but it said "suarting DOS" instead of "starting DOS" (replaced the T with a U) and hung there. The CF card isn't corrupt or anything, I've used it several times since then. Haven't seen that before.
Things I've tried...
- Removed and reinstalled everything at least once
- Tried a different, better, and known-working power supply
- Swapped RAM sticks out, tried different combos including just one at a time
- Swapped the DX2-66 for a DX2-50 that I have on hand, adjusted jumpers accordingly
- Double checked all jumper settings
- Disabled L1 and/or L2 cache in the BIOS (separately and together)
- Changed L1 cache from write-through to write-back (with and without L2 disabled)
- Reloaded default BIOS settings
- Checked controller card on a different motherboard and it works fine booting a floppy
So at this point, I'm starting to think it might be likely a fault with the motherboard. Which would be a real shame! The only reason I started this 486 build was because I was able to get this motherboard at a decent price. I've looked at other 486 boards on eBay a few times over the last couple of weeks, and there's definitely nothing for a reasonable price.
I don't know if I ever mentioned in this thread, but this motherboard is warped pretty good. I could try and reflow the legs of the QFP chips, but, ugh. I don't have a microscope, so I can't examine the board well enough for cracked solder joints.
Putzing around with these old computers is something I do from time to time as a stress reliever. It takes no mental effort on my part, and whatever results are of no real consequence. A couple of years ago I was even willing to mess around with motherboard repair. But for right now, I'm just too short on time and energy for this kind of thing. And I'm kinda bummed that I wasted a couple of hours today troubleshooting this motherboard. And I have to consider that it might have a fault that isn't repairable. So I've been considering my options with this.
I may troubleshoot this a little more, especially if anyone has any suggestions. And I may post on the Vogons forums for help with it. But I'm not sure how much more time I'm willing to sink into it. So that said, I've been considering my options. And here's one I've come up with...
Swap the motherboard for another AT board that I already own.
The thing that sucks about that is that this is the only 486 board that I own. So swapping motherboards kinda kills one of the biggest purpose for this build: To use the legendary DX2-66. After thinking about it some, it still would be a DOS AT build, it would just be a different CPU. Would I really even notice or care after a while? Still, part of it was just to smile at the fact that I was using the quintessential 486 CPU. LOL good thing I decided against getting that DX2-66 case badge!
So I have the DTK Socket 7 board (picture here) that I could use. It's actually a really nice board. It's still AT, so it can fit in the same case. And in a lot of ways it's a better board. I mean, aside from the obvious of the better CPU socket. It has PCI slots, on board I/O controller, USB, and a header for a PS/2 mouse (which would be better than using a serial mouse). I mean, externally you wouldn't even be able to tell a difference. So does it really matter?
One thing that sucks about this route though is that the DTK board has PCI slots but no VLB. I went out of my way to pick up that VLB video card, and although I got a good deal on one it still wasn't cheap. I have zero use for it outside of the 486 board. So that kinda sucks. On the flip side, if I use the DTK board with a PCI video card then I never really have to worry about any performance issues.
And speaking of performance... The DX2-66 could be slowed down with the turbo button, to 33 Mhz I guess is what it does. But to be honest, there really aren't any games I'm interested in that are speed sensitive. And even if that changes in the future, there are other ways to deal with it. So I'm not worried about it. The DTK board doesn't have any turbo function, but it does have a header for a turbo LED. Apparently this was a thing LOL. From what I'm reading, it literally just lights up the turbo LED and has no other point to it.
In regards to the CPU that I would use with the DTK board, right now I have an AMD K5 75 MHz installed on it. From what I'm reading, it's about on par with a similarly clocked Pentium. That combined with a PCI video card means that I'll have a better performing computer overall. And I'm probably better off because I'm in better shape with backup stuff if anything fails. Like the VLB video card, I would be screwed with the 486 build if that card ever died. But a PCI video card, I already have backups and even still they are cheap and plentiful on eBay compared to VLB cards.
So I don't know, I think I'm gonna go with the DTK board for now. It'll still be a dedicated DOS 6.22 computer. It's just a shame that it wont be a DX2-66.
And this thread title will have to change. And this doesn't mean that I'm giving up on the 486. I can always troubleshoot the stupid PC Chips board more, if and when I have the time or am feeling up to it. And I still could be on the lookout for a 486 motherbaord that doesn't cost an arm and a leg. Although at this point, if I were going to get another 486 board I would want to try and trade up. And all the while I could be enjoying this PC actually working with the DTK board. Should I ever fix the 486 board or get another one, I could always swap it in.
Re: My i486 DOS PC Build - Possible Motherboard Fault?
If it works up to that point, I'd suggest flash a slightly older than last bios to a different eeprom bios chip. Weird things like this are hard to tackle but I pulled a lot of hair out in a similar situation before finding out why everything *almost* worked.
