Keep in mind that dx25 is a pretty uncommon cpu, so might be worth holding on to ..

Of course I'm not trowing it away 😀 I have a small collection of 486'es that will put that in, until maybe i sell the system one day and revert it to original.

BTW I also have a problem with the harddrive. Its a Conner type 17. (41MB) It was set up as a type 8 in the BIOS. I dont know if that did something to it or not but i set it to type 17. I was able to read a lot of files with no problem, but some had errors. I ran Scandisk, wich said it could not write to the file allocation table. I deleted the partition in Fdisk and tried to make a new primary partition. Fdisk just freezes. After restart the new partition shows but i cant write to it or format it. same thing happens over and over. Is the drive dead? Or do i need to use some other software?

Kind regards

That's one awesome early 486 pc. I love how that pc looks and it must be built like a tank. From what year is it?

I'm afraid that it is has proprietary memory modules.

You probably won't be able to upgrade it to 66 MHz because it has a 25 MHz FSB. The Intel OverDrive DX2ODP50 and DX4ODP75 might work though.

Maybe the MBR on your hard disk is corrupt?

Yeah its pretty solid, the cover is steel, but the bottom and back is tick plastic. The BIOS chips are marked 1990 thats as much I know about the age.

Ahh thats what i was afraid of. Anyone know if something else uses these modules? I cant find any on ebay.

I was hoping the FSB where selectable, i know that board was delivered with 33mhz CPUs too. Right by the CPU there are several crystals, 50mhz, 14, 16 (clock doubling?). further away, 37, 25, 28, 44, 12.
If i can use an DX2-50 that would be okay too. That would be drop in right?

Found a Northon emergency disk. Unformat says the system area is physically damaged on the HD. 😒 I guess i have to find a replacement.

NCR also used 64 pin SIMMs, but they probably aren't any easier to find and may not be compatible.

Great looking machines! Hard to find OEM computers around here. Most of them are probably already rotting away in some landfill.

The SIMMs look like the 64pin SIMMs used in Apple and Amiga. If they are compatible with AST i dont know. Anyone know what happens if you put Amiga ram in an Apple or vice versa?

The hard drive is dead, long live the new hard drive... I opened the Conner and inspected the plate, it got scratches 😒 Do anyone know what brand is the most reliable in the <500MB range of IDE drives? I want the systems to be period correct so im looking for a IDE drive.
I have a Conner 115~ MB drive in the Copam, I hope thats not the next to go.

@Half Saint
Yeah they are not as easy to find anymore, I should have started this hobby before most got scrapped. But I was lucky to find these, the Copam i got for free from a old IT guy that bought it new. The AST i got for free from a company that was going to scrap it. 😁

I believe the 64-pin RAM in the AST was also known as "CUPID memory", because these machines also used a CUPID expansion bus that was used for RAM cards and CPU cards.

SVD wrote:

Yeah its pretty solid, the cover is steel, but the bottom and back is tick plastic. The BIOS chips are marked 1990 thats as much I know about the age.

You might find date codes on various IC's or on the power supply.

SVD wrote:

Ahh thats what i was afraid of. Anyone know if something else uses these modules? I cant find any on ebay.

I have a couple 64-pin memory modules. What for DRAM chips do your modules contain (brand and model number)?

SVD wrote:

I was hoping the FSB where selectable, i know that board was delivered with 33mhz CPUs too. Right by the CPU there are several crystals, 50mhz, 14, 16 (clock doubling?). further away, 37, 25, 28, 44, 12.
If i can use an DX2-50 that would be okay too. That would be drop in right?

It seems like you know more than I do. The DX2-50 also works on 5V, so you can give it a try. You'll probably need to change some jumpers though (if it supports that CPU, which I doubt, because this is an early 486 pc). The Overdrive CPU's should in theory work fine anyway.

SVD wrote:

Found a Northon emergency disk. Unformat says the system area is physically damaged on the HD. 😒 I guess i have to find a replacement.

You might as well replace it with a CF card adapter and a small CF card.

The CPU is 1989 and the late HD is may 1991

Super! what size? The 8x DRAM chips per sim are marked MCM514256AJ80 UQQHU9049. and there is a 9'th chip marked T JAPAN 9024HCK TC514266AJ-80

There are DIP-switches that are "factory set" i think it might be those.

I have been thinking about a CF adapter, but i want the authentic sound and spectacle :p I tried SCSI but my only SCSI adapter does not have a BIOS so that did not work...

Does BIOS allow you to set your own HDD geometry or are you stuck using Type 1, Type 2, etc.
I'm going to assume bios limit is 500MB going from the age of the PC but you can add something bigger and see how much is recognised as a simple test.
I use a HDD for C:\ and CF for everything else. this way I get the authentic sound at boot, then something fast and reliable while playing games. bonus is the HDD can be quite small as Dos takes almost nothing.

Re brand, just like now, 1 person will say x brand is the best while the next person will say that's the worst brand. Just go with what you can get. we are talking about a HDD that's 20+ years old, its going to come down to luck now.

Interesting PC, looking forward to seeing what you do with it 😀

If we can assume that a MCM514256AJ80 is a standard 80ns 256kb x 1 (tried googling, got stuck in reseller hell before finding an actual data sheet) then we can rule out Apple 64 pin SIMMs as they are dual ported from memory. I'd check the NCR board I have somewhere that's full of 64 pin SIMMs, but I'd have to find it first.

The BIOS allows for setting your own HD geometry.
Yeah I'm leaning towards an HD/CF combo. I guess I could get a few of those adapters.

@dr.ido
actually i think each chip are 4x256kb. each simm is 1MB.

I have an AST Advantage 486SX/25. It's a re-buy of the first PC I ever bought. Mine uses normal(-ish?) 72-pin SIMMs so I can't help with the memory. The BIOS on mine is indeed limited to 500MB - but does support auto-detection.

Both this new (to me) one and the original I bought new back in the early 90s came with Western Digital drives. OG was 85MB, this one was 170MB. The old black-case Caviar drives seem to be really reliable, but the silver ones ... ugh. I've bought about 9 of them, and 6 were dead or on death's door, two had bearings so screechy that sudden failure was not far off, and one is working OK ... for now. I have a couple of small Conner drives too. One has some bad sectors but is otherwise OK. The other is fine.

Got any old 5.25 2-4gig BigFoot drive, or for that matter 3.25" hdds, laying around? I use one in my 386DX25 using EZBios. Works wonderfully. A DX2/66 will just run as a DX2/50 if there are no jumpers to change. You might be able to get an isa adapter which takes 30 pinnram to add extra.

Build your own cloning the existing simm pinout

https://elcodis.com/parts/241509/822033-2.html

Laser printers, Zenith, NEC, GBP amiga accelerators, servers and other machines used 64pin Simms whether there was a standard between them I have no idea you would need to trace out your modules

Other option would be to build an adapter from 72 to 64

IIFX SIMMS were dual port 64pin

Too bad so little information survives on obscure models.

Odd duck indeed

https://stason.org/TULARC/pc/motherboards/A/A … AVO-486-25.html

http://www.1000bit.it/ad/bro/ast/AST-ProductBrochure.pdf

http://www.ec.kingston.com/ecom/configurator_ … rtno=KST8000/33

https://wikivisually.com/wiki/SIMM#GVP_64-pin

It's kind of amazing how shallow the Internet's knowledge pool actually is. Finding info on 90s hardware is surprisingly difficult. It IS nice to have as much as we do, don't get me wrong, but I am surprised at how often information is just not out there to be found. Those were dark days indeed. 😀

I saw a listing of BIOS versions from what looked to be a catalog from a BBS or something. It showed a later version (including a filename!) than what I have in my Advantage. I was really hoping I could find it, and it might lift that 500MB barrier. (I only know about this limit because I needed more space and installed a 700MB drive, then couldn't use it all.) Alas, no luck.

About the RAM I'm thinking I will just buy 2x 4MB AMIGA SIMMs and see if they work. Adding an ISA adapter to a 486 is a bit backwards is it not? its going to be limited to 16bit 8mhz on a 32bit 25mhz computer.
Im going to bring my 486 CPUs back home this weekend, then Im going to test an DX2/50 I have.

I read the Amiga RAM will not work with AST, if they do please let us know. At the end of this I have some solutions for you. The Bravo did not use the Cupid32 "semi"modular system as it was a lower end offering, and had a standard system board onto which the cpu was mounted, but in the case of your 486/25 it did use the same 64-pin ram, limited to four 4mb chips for a total fo 16mb. Lesser model Bravo's including the 286 and 386's required different Page Mode ram. Bravos were not compatible with the optional Memory Expansion Board designed for the cupid32 based systems. Chances are that a DX50 or even a DX33 will not work because the DX25 was the fastest CPU available in the Bravo line in 1990. There was a guide that listed compatible systems for Intel Overdrive CPU's, but I can't find it online anymore. My guess is, you would need the bios and/or keyboard controller chip from a '91 or newer system installed to support newer cpu's. I have an AST Premium II also from 1990, and when upgrading the CPU via the factory cupid32 Fastboard DX66 upgrade (1994), a new bios chip had to be installed on the system board for the CPU to be recognized. These Fastboard upgrades were customized packages featuring all parts / software needed based on your systems bios version. Some systems also required the keyboard controller update, while in others, the bios could be software updated. I do have 2x 1mb RAM modules that will work with your system if you are interested in purchasing them, to give you a total of 4mb, just enough to run Doom if using a boot disk. A matched pair on eBay currently is listed for $50, I will sell mine for $40. Also check eBay for the cupid32 cpu upgrade boards, they are common $80-$120, several are currently available as of this writing, and they mostly came populated with 2x 4mb chips that would also be compatible with your system, so you could potential have 10mb. There is one now that has 16mb, you could buy that, install the 16mb into your system, then resell the cpu board populated with your old 2mb of ram.