Please post pictures of everything as well as listing specific brand and model numbers of the parts you are using.

It could be a compatibility issue somewhere.. yes, even though you have tried multiple different things.

It could still be your PSU despite multimeter readings. You could pick up an ATX to AT adapter and use a more modern PSU just to eliminate that variable.

As for resource conflicts - the keyword from cyclone3d's post is "everything."

Motherboards:

Graphics cards:

Cards with floppy interface:

PSU:

Keyboards used for testing. Middle one is only one with din and top and bottom ones are ps2 keyboards and I had to use adapter with them.

Display used for testing:

Floppy drives and floppy cables used for testing:

I believe that is everything I have used during testing

Basically strangest thing is that with all the motherboards and all the cards with floppy interface exactly same thing happens when there is the table above with all the hardware info after posting and it is suppose to start loading dos from the floppy disk. The floppy drive light turns on for a second or two and then it turns back off and nothing else happens.

Make sure to pull those barrel batteries off of all of the boards, they can corrode and destroy them. Hopefully they haven't started, or done major damage.

cj_reha wrote:

Make sure to pull those barrel batteries off of all of the boards, they can corrode and destroy them. Hopefully they haven't started, or done major damage.

First post said that those are brand new batteries.

Wow. You really have a lot of variables there.

For you to change out that many things and have problems - I almost want to bet money against your PSU.

I am just spitballing, but you could:
1: Pick a mobo - Maybe the SiS DX2-80 with VLB
2: Choose an I/O card. Disable COM1 (IRQ 4), COM2 (IRQ 3), Parallel (IRQ 7), etc (probably no point to this). Make sure address ranges are set to the card's default
3: Pick a VGA card (ET400AX). Disable IRQ2

Put your cards in and boot. Hit the BIOS. Load power-on defaults. Disable internal and external cache. Slow the AT bus speed manually - either by using a higher divider or by selecting a manual speed.

I don't really know that that is going to let you hit your boot sequence at all - ideally you grab an adapter and try it with another power supply.

Thanks. I have been on the lookout for another PSU. I have another AT psu that doesn't work. It makes noise for a second when you try to start it like it is trying to start the fan and voltages go up for a second too and then the voltages drop back to zero.
I should probably buy an adapter but that would generally be another month before it gets here when buying from ebay and no idea if it would actually help. I have not changed much in the bios of these motherboards. After bios defaults I have just generally set the time and date and set the A: floppy as 1.44Mb.
Process of elimination has been what I have been trying to do with these hardware. All that is left seem to be the really unlikely options like all the motherboards would have failed in exactly same way that prevents booting or that the psu has some strange problem where 5V and 12V are fine and it allows graphics card to work and motherboard to post fine while causing floppy drive not to work. Only thing I noticed with the voltages was that when it did the floppy seek and floppy drive made the normal noise related to that the 5V from the molex measurement dropped from 5.05V to 4.95V and then returned to 5.05V.

I finally recently found myself an AT case for this project and I got those new batteries for the motherboard, so I was hoping to finally being able to build the retro gaming pc.

cyclone3d wrote:

cj_reha wrote:

Make sure to pull those barrel batteries off of all of the boards, they can corrode and destroy them. Hopefully they haven't started, or done major damage.

First post said that those are brand new batteries.

Oops. 🤣

I have an update to this project. No luck with floppy drives yet, but I managed to borrow an ide hard drive with dos 6.22 preinstalled. Both of the IO cards seem to work fine when booting from hard drive, except that the motherboard that has 486 33Mhz gives an error "EMM386 not installed insufficient memory" which is kind of funny because it has the highest amount of ram out of all the motherboards. Any ideas about that?

Another thing is that the 386 33Mhz seemed really slow, no matter if I did set the set system boot cpu speed in bios high or low. I only got 3.3Fps in 3dbench and 2.4 in speedsys benchmark. It only started running at normal speed when I did put a jumper on 2 pins of the 3 pin turbo switch connector on the motherboard. After that I got 12.5fps in 3dbench. and 7.27 in speedsys.
Is it normal that these old motherboards run at slow speed no matter what when nothing is connected to the turbo switch connector on the motherboard?

I managed to borrow another AT psu. It solved some problems, but there seems to be others. The motherboard with 33Mhz 486 cpu now boots from floppy if I use the winbond IO card, but it has problems with ram. I first get error that unreliable xms detected at address 00100000h and the main thing is that the address doesn't change no matter if I switch all the simm modules and if I make himem.sys bypass the memory testing, emm386 gives error "insufficient memory" like I said in the previous post.

The motherboard with 33Mhz 386 still doesn't boot from floppy disks and if I boot using hard drive with pre installed dos 6.22, it boots fine but when I try to access any floppy disks, "dir" shows all the disks as empty and chkdsk gives alot of allocation errors.

Only motherboards that boots both hard drive and floppy disk with the winbond IO card without any problems is the VLB 486 motherboard after testing with the other psu. Floppy booting doesn't seem to work using the goldstar IO card with any of the motherboards still, so that IO card might be broken.

Any ideas if there is anything I can do with those motherboards that have memory errors and can't read floppies?
The motherboard with 486 33Mhz cpu has 256Kb of cache while the others have only 128Kb. Would it work if I moved cache chips from the motherboard that has 256kb cache to the VLB motherboard?