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First post, by nathanieltolbert

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First thing, I am not 100% certain that this board supports DX4 chips. It does support 3.3V processors because I had a 486DX2-66V from AMD which runs at 3.3V working just fine in the system. The motherboard is an absolute mystery to me. The system is a Techmedia NOS system I found online, and I can furnish pictures of the motherboard. It has a CR2032 battery holder soldered directly into it. I did this, and yes, I know I need to add a resistor to it, but I don't know what value, and I didn't at the time of installing it. The board has integrated Dual IDE and Floppy as well as a Cirrus Logic Video, a CL-GD5428. The system works fine with 3.3V or 5V when setting the jumpers correctly. So here's the strangeness. I took out the DX2-66V chip, and I installed the DX4-100. The jumpers are set for DX/DX2. There is no mention on the silkscreening anywhere that I saw on casual observation for DX4. But I wasn't certain that no marking for it would be an issue. I was under the impression that the bus multiplier was internal to the CPU. So I boot the machine up and it boots, counts up the 16MB of RAM and on the System screen as it loads DOS, I see it lists the Processor as a 486DX2. Strange, I thought, so I let it boot all the way to dos, and then I loaded up Phil's Computer Lab DosBench and ran the Check CPU program. It cannot identify anything about the processor except that it's a 486DX2 and it's running at 67.1 MHz. This was really strange to me because there has always been stepping information and what not. I don't know if I have something configured wrong, or if the board for whatever reason doesn't allow a higher multiplier than two. I can't even find any information about this motherboard online while searching. I know it's rebranded. It's a Markvision Flexboard ver 2.1 h21D? I have a picture of the board, because when I originally ordered the system, the PCB that came with it was dead, and we couldn't get it to work at all. The thought was Battery corrosion that I cannot see, so if anyone wants a project I got a board. 😀 But I digress. If someone can take a look at the board picture and see if there is a jumper setting that is supposed to be set or if anyone can find information about this motherboard, I would be really appreciative. The stunning variety of make and manufacturers of 486 boards and systems is just staggering at times. Also, one more question, when I upload a picture that I take of my parts, which file license do I use? Thank you for taking a look and any suggestions that you may have. I very much appreciate the help.

Regards,

Nathan

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Reply 1 of 66, by nathanieltolbert

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One more possible question. Is it possible that I got duped and someone rebadged a DX2-66 processor? I am trying to get my pictures to upload, but I am having some issues. I did take a picture, and I will post it as soon as I can. But is it a possibility that I got a fake CPU?

Reply 2 of 66, by chublord

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On my machine, my DX4-100 shows as 100 MHz with a 33 MHz FSB (3x multiplier), but shows as 80 MHz with a 40 MHz multiplier and 100 MHz at 50 MHz FSB (2x mulitplier). So the multiplier can be controlled from the motherboard.

I had a strange experience with a recent DX4-100 I purchased on eBay that seemed to be a fake chip. Where did you get yours from?

IBM Valuepoint 486 DX4-100, Opti 802G, 50 MHz FSB, Voodoo1+S3 864, Quantum Fireball EX 4.0 GB, Seagate Medalist 1.6 GB, 128 MB FPM, 256k L2

Reply 3 of 66, by nathanieltolbert

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chublord wrote on 2021-09-06, 16:11:

On my machine, my DX4-100 shows as 100 MHz with a 33 MHz FSB (3x multiplier), but shows as 80 MHz with a 40 MHz multiplier and 100 MHz at 50 MHz FSB (2x mulitplier). So the multiplier can be controlled from the motherboard.

I had a strange experience with a recent DX4-100 I purchased on eBay that seemed to be a fake chip. Where did you get yours from?

I also bought mine from eBay. There are no local eWaste sellers here where I live. We used to have one but they didn't sell to collectors because they 'didn't want to have to deal with the fighting.' Got to watch them shred Amiga A1000's and early run Macintoshes along with 5150s because of that. Surprisingly, they went out of business! I wonder why? /s But yes, I bought mine from eBay. Seller had a high 90-something % positive feedback, so I thought I might be safe, and it did ship from inside the US to me, as far as I can tell.

Reply 4 of 66, by nathanieltolbert

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Okay the pictures finally uploaded from my phone. So the CPU and the AMIBIOS system configuration screen, and finally that is what I see when I run the Check CPU program in the Dosbench folder. Maybe this can help?

Regards,

Nathan

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Reply 5 of 66, by Disruptor

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Well, the Am486DX4 NV8T has a different jumper layout than the Am486DX4 SV8B which has likely the layout that an Intel486DX4 has.
Please try to use the 486DX2 setting first, but with 3.3 Volts. I mean, exactly the settings you've used for your 3.3 Volt Am486DX2 before.
The 2/3x multiplicator jumper is the same that switches the SV8B / Intel DX4 from write through to write back operation.

Reply 7 of 66, by Disruptor

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Look at the manual at http://datasheets.chipdb.org/AMD/486_5x86/19160D.pdf

CLKMUL
Clock Multiplier (Input)
The clock multiplier input defines the ratio of internal core clock frequency to external bus frequency. If sampled Low, the core frequency operates at twice the external bus frequency (speed-double mode). If driven High or left floating speed-triple mode is selected. CLKMUL has an internal pull-up to VCC and may be left floating in designs that wish to select speed-triple clock mode.

You may have to check how the CLKMUL pin B-13 is connected. Perhaps it goes to a jumper. You should check this with a multimeter.

Reply 8 of 66, by Deksor

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According to here : http://www.win3x.org/uh19/motherboards/8470
This board shares the same jumper settings as these boards http://www.win3x.org/uh19/motherboards/?manuf … rId=82&name=uiv

Would you like to dump your bios so I can add it to the page please ? If you need help, tell me 😀

Trying to identify old hardware ? Visit The retro web - Project's thread The Retro Web project - a stason.org/TH99 alternative

Reply 9 of 66, by nathanieltolbert

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Regrettably I don't have the tools to image the BIOS. Is there a program I can run from DOS or Windows that would allow me to image it to a file that I could then get to you? I have been meaning to get an eeprom or eprom programmer, but I haven't gotten around to it yet.

Reply 10 of 66, by Deksor

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Sure you can, use this program : http://cd.textfiles.com/microhaus/mhblackbox3 … MORY/GETROM.ZIP

Trying to identify old hardware ? Visit The retro web - Project's thread The Retro Web project - a stason.org/TH99 alternative

Reply 11 of 66, by nathanieltolbert

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Sorry for the delay in replying to the information provided. Those jumper settings did indeed work! It's now booting at 100MHz and identifying as a DX4. New strange though. I'm sure it's a jumper setting, but I am getting a DMA conflict for the sound card. I cannot seem to set DMA1. Everything else within CTCU shows fine, but DMA1 fails every time. I'm not sure why. I checked the jumpers on the board for LPT1 and it's set to DMA/DACK 3 and I tried using MSD to look at my system info, but I could not see where I could see DMA usage. I saw IRQ though. Any additional help would be really appreciated. If it's something to do with the sound card, and that's always a possibility (All I have that's not in use is an AWE64 Value card) any way I can diagnose that would be appreciated.

Reply 13 of 66, by nathanieltolbert

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Disruptor wrote on 2021-09-09, 21:18:

What happens with other DMA channel? 0 or 3?

Well that's the strange thing. For whatever reason, the CTCU won't let me change the DMA to anything else. I'm a little confused, but then again, I haven't ever used an AWE64 with Windows 3.11 and Dos 6.22 before.

Reply 14 of 66, by BitWrangler

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I'd try it in a different slot, just in case you've got one with iffy DMA contacts or traces.

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.

Reply 15 of 66, by nathanieltolbert

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Okay, downloaded a newer version of CTCU and ran it. I was able to change my DMA. DMA 3 fails, along with DMA 1, but DMA 0 works. So there is an obvious conflict on DMA 1. Is there an easy way to identify what is using DMA 1 so I can move it?

Reply 16 of 66, by nathanieltolbert

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BitWrangler wrote on 2021-09-09, 22:23:

I'd try it in a different slot, just in case you've got one with iffy DMA contacts or traces.

Good Idea give me a moment to change where it's plugged in.

-Edit- That did not change it. So I guess that means there's a DMA conflict on the board somewhere. Is it possible that it's my Graphics card? I am using a VLB video card, an Ark1000 card. I don't know if that causes issues or not. There are jumpers on the board for LDEV and I was curious if that meant that DMA was reserved for the VLB slots as well as everything else? This is the first system I have had that has VLB. Even back in the day we went from a Packard Bell to a motherboard with PCI.

Reply 17 of 66, by nathanieltolbert

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Okay. I think I got it figured out. Even though the board has only 1 LPT port, it had a jumper to enable LPT2/LPT3 and it was set to enable, I changed that to disable, and then double checked that the LPT1 port was set to DMA3 and tested it. DMA 1 was working with the soundcard then! Boy howdy is this card noisy! Still, it works, and provides Adlib-ish music and SB/SB16 PCM sound. But there is a lot of noise on the ISA bus on this machine, I can hear with the CD-ROM drive spins up and the hard drive accesses. But the CD-ROM didn't have the audio cable connected yet. Thank you to everyone for the suggestions and the links to information that I just couldn't find. I really appreciate the help and now the machine is running like it should! I will post a picture of the machine here when I have it set back up on the table. 😀

Reply 18 of 66, by nathanieltolbert

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Okay, so I got the DMA1 issue fixed, but now I have another strange one. I have my HardMPU card that is set to I/O 330 and IRQ 2/9, and I cannot get midi to play when I use Hardmpu.com -s to show the current config it gives an error - ERROR: Timed out waiting for DSR. When I open MSD and look at the IRQ addresses I see IRQ2 is active and used by Second 8259A and looking at IRQ9 it says it's redirected to IRQ2. Is there a way to move forward to try and get this to work? Or am I going to need to set the MPU card to a different IRQ? I would have thought all of my other machines would have something similar with the 8259 chip, but I haven't encountered this before. Thank you again for any help or suggestions I can try.

Reply 19 of 66, by BitWrangler

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VGA sometimes has IRQ9 enabled, I don't think most things need it to be.

Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.