Fixing up some old 486'es! (Ram and bios issues)

[Mod_Man_Extreme]

Recently I've been bitten by the DOS bug and have gone out in search of a nice system to both play old DOS titles on, and also have proper period correct compatibility with any old ISA sound cards I may wish to use. It took me a bit but eventually I ended up with quite a few different machines and pieces of hardware.

While I managed to find a couple of Pentium machines (all P2' & 3's) and got everything up and running my holy grail was an attempt to find myself a really nice 'slimline' style system similar to the Unisys CWD line. As I prefer to find my hardware locally whenever possible this lead to a lot of fruitless searching until finally I bumped into a pair of DIGITAL DECpc LPV+ 425SX machines at my friend's old record shop. He was clearing out his back room and had long since thought that all of his original POS terminal PC's had been sent off to the recyclers. Lucky for me I got a matching pair of units so I have a complete set of spare parts. Also including the ability to steal the extra memory/zip chips off of one to upgrade the video RAM on the integrated S3 S3 86C805 (should be on an integrated VLB bus if I'm correct) from what I've seen. Both are 486SX's running at 25mhz, have 4MB of ram, one 615mb HDD, one 1gb HDD, and the bundle included 1 matching DIGITAL branded monitor and several mechanical Cherry branded keyboards (some with card readers, lol). Aside from having some very dusty innards they both seem to be working perfectly so far, and support 50MHZ 486 upgrades. However, when I tried upgrading the RAM from the stock 4MB I was greeted with several error messages and lots of angry beeping.

The DIGITAL brand, with 'Digital' meaning made by the Digital Equipment Corporation, which makes searching for info even harder as you won't get very far beyond generic results when looking for a 'digital' computer, lol. According to the information I've managed to find while looking at online these machines should support up to 32MB or 64MB of ram at maximum and only through either 72pin 4MB or 16MB simms with a latency of 70 or less. However whenever I add any of my existing 4MB Simms it refuses to boot, 8MB simms that meet the relevant requirements show up as 4MB simms along with the original one that came with the machine. Unfortunately I have no 16MB simms to check with compatibility wise. Secondly, the machine has started giving me 'Incorrect memory configuration' errors even with the original NEC branded ram stick installed back into place. I'm not sure where to go from here, and am completely and utterly lost in terms of what I'm doing as I grew up in the Pentium era. As a total newbie to anything 486, XT or AT it's a bit like incomprehensible black magic and incredibly rare here in NC.

I was unable to find ANY support for these online anywhere which is disappointing. According to some sources on a few forums Compaq used to have all of these drivers available as a part of their legacy support site as recently as 2010-2012 (Compaq/HP bought out DIGITAL in the mid-90's), but I had no such luck finding any. When I went around following any of the links I found on various other forums, and even going so far as to call HP/Compaq's support number, I pretty much hit a dead end. I was hoping to update the BIOS as it seems that there were several revisions thanks to both an archived eBay listing which shows a picture of a 1.04 BIOS (mine are 1.00) and the service manuals stating the maching accepts up to 64MB of RAM. The service manuals were both printed in 1996, a year after the computer's release, but make no mention of either the BIOS or anything else when stating upgrade capacities. I'm hoping someone is a fellow vintage PC nut and can help me out or potentially proivide BIOS upgrade files, or tell me what I need to look for when it comes to RAM or anything else.

Also, these machines use a clock 'chip' and not a traditional lithium/coin battery. How exactly does oner go about replacing these? Can they go bad and/or explode like older AT and ATX batteries, or are they driven by some sort of long-term charge, etc...?

Finally, I linked both the service manual, and service guides, for anyone who is interested in helping out to have all the most complete information I could find. Any advice or info from vintage PC gurus would be appreciated!

Service Manual:
http://manx.classiccmp.org/collections/ ... 000018.pdf

Service Guide:
http://manx.classiccmp.org/collections/ ... 0wwsva.pdf

I posted a sister thread over at VOGONS to see if anyone over there knew about these machines but, hopefully I'm not in the dark too long.

[Anapan]

Maybe one of those PCI diagnostic cards could return a useful error code and help you figure out the problem. There's a bunch of them on Deal Extreme.

[Exhuminator]

Any advice or info from vintage PC gurus would be appreciated!

Throw this stuff away and use DOSBox.

Here's a few thoughts though as to actually fixing the problem:

The first thing I would do is reset the BIOS back to factory defaults. This might already occur every time you power on the machine considering the RTC is kaput. Just make sure the "ROM based setup" option is Enabled though.

Page 35 of the service manual shows memory bank configurations. Make sure you've got your SIMMs plugged in sequentially in accordance to that chart. Although it's possible one of the SIMMs may actually be bad?

I would definitely use the beep code chart on page 52, and see if it tells you anything when the computer beeps angrily.

As for the RTC, looks like the part number is 21-39125-01. Considering you now have the part number and know the manufacturer, you might be able to find one on eBay. Or a specialty vintage computer hardware website might have these in stock.

Personally if I was going to have an actual 486 DOS PC, I'd go and find one with this processor: https://en.wikipedia.org/wiki/Intel_80486DX2 Probably a Dell PowerEdge XE would be great.

[Anapan]

I got a lot of game time out my 486 DX2 66. I loved that machine so much. There's still some games (turrican and tempest 2000 with their custom VGA modes that I recall) and demoscene demos that will only work on a real PC. I used to use Game Wizard a lot too, and that as well will not work fully on dosbox (EMS/XMS searches hang it). Some of the late 3D game releases won't really work well either - Dungeon Keeper 2 comes to mind.
There's something to be said about running the games on an old PC with an SVGA monitor (scanlines!), and a mechanical PS/2 keyboard.
The true OPL2/3 soundtracks sound slightly different than any emulation I've been able to recreate (I've had week and month long email conversations with guys asking for help getting that same sound with multiple attempts on both our sides using every emulation engine I could come up with and we could never seem to quite get it right (based on aux-out recordings they provide).

It's certainly a worthwhile endeavor to build a pimped-out DOS machine. I still drag mine out and hook it into my surround sound system and Framemeister once in a while. My latest one is a Libretto 100CT - VHS sized with a true Yamaha soundcard and a 800x480 LCD.

[Mod_Man_Extreme]

Maybe one of those PCI diagnostic cards could return a useful error code and help you figure out the problem. There's a bunch of them on Deal Extreme.

Unfortunately this machine is strictly ISA only, but even then it's old enough that there's no plug and play support in the bios for PCI either if it were to have had a slot.

Throw this stuff away and use DOSBox.

LOL, no. I picked this stuff up to get away from the glitch-box that is DOS-BOX. I've had enough graphical maladies, wonky audio and games refusing to boot letting me know it wasn't worth using for any serious gameplay.

The first thing I would do is reset the BIOS back to factory defaults. This might already occur every time you power on the machine considering the RTC is kaput. Just make sure the "ROM based setup" option is Enabled though.

Page 35 of the service manual shows memory bank configurations. Make sure you've got your SIMMs plugged in sequentially in accordance to that chart. Although it's possible one of the SIMMs may actually be bad?

I would definitely use the beep code chart on page 52, and see if it tells you anything when the computer beeps angrily.

As for the RTC, looks like the part number is 21-39125-01. Considering you now have the part number and know the manufacturer, you might be able to find one on eBay. Or a specialty vintage computer hardware website might have these in stock.

Personally if I was going to have an actual 486 DOS PC, I'd go and find one with this processor: https://en.wikipedia.org/wiki/Intel_80486DX2 Probably a Dell PowerEdge XE would be great.

Well, it turns out that one of the RAM sticks was actually of the improper latency despite it's label. As a result I would get the error beep and the system was refusing to boot no matter what I did. A swap with some NOS RAM from eBay and I managed to upgrade the system to it's maximum of 64MB for the cost of a cheap burger. The beep codes chart was of little use unfortunately. Whenever I tried to decipher the string of beep it just kept on giving me a sequence that wasn't listed in the manual and had me attempting all sorts of stuff in general to see what was amiss. But, luckily I have an ATX board with 72-pin slots that I used to test the RAM after I had posted this thread which led me to find the mis-labelled stick.

The clock batteries are actually A-OK, fortunately. When I went onto a full tear-down I found that they were the newer part number which superseded the original yo posted fromk the manual. After checking with my buddy who owned the record shop he indeed confirmed that they had been serviced sometime in the last five years or so, and the batteries were changed at that time. So, they're relatively fresh and in good order as to not cause any errors when powering-on from a cold-boot.

I'm actually getting ready to go ahead and to a CPU upgrade soon and have settled on a 486DX-4 100mhz. Luckily it supports running in a 50mhz state, which is the maximum speed supported by the board, and should give everything a very nice boost performance wise over the lousy 25mhz SX CPU currently installed. Otherwise it's a 50mhz DX2 if I can't use the DX4 for either voltage differences or some other reason.

While I would potentially consider something newer or different, and have also collected a few other nice DOS compatible machines (including a 500mhz Mendecino Celery powered HP micro-tower that's my current retro rig), I prefer to use this one due to it's incredibly small size and form factor. It's a pizza box style case, so that has a lot going for it when you also take into account that it's not a monster which eats up my limited desk space.

I got a lot of game time out my 486 DX2 66. I loved that machine so much. There's still some games (turrican and tempest 2000 with their custom VGA modes that I recall) and demoscene demos that will only work on a real PC. I used to use Game Wizard a lot too, and that as well will not work fully on dosbox (EMS/XMS searches hang it). Some of the late 3D game releases won't really work well either - Dungeon Keeper 2 comes to mind.
There's something to be said about running the games on an old PC with an SVGA monitor (scanlines!), and a mechanical PS/2 keyboard.
The true OPL2/3 soundtracks sound slightly different than any emulation I've been able to recreate (I've had week and month long email conversations with guys asking for help getting that same sound with multiple attempts on both our sides using every emulation engine I could come up with and we could never seem to quite get it right (based on aux-out recordings they provide).

It's certainly a worthwhile endeavor to build a pimped-out DOS machine. I still drag mine out and hook it into my surround sound system and Framemeister once in a while. My latest one is a Libretto 100CT - VHS sized with a true Yamaha soundcard and a 800x480 LCD.

That's been exactly my goal in building this system. The games as they play and sound always seem to run off somewhat for whichever reason in DOS-BOX. Whenever I play them on real hardware they work, look, sound and play like they should. Not to mention that the experience is consistent, which is a very big deal for me.

Also, I love Librettos and all the neat, unique hardware that manufacturers tried out during the mid-90's era. Unfortunately the Librettos are getting quite pricey as time goes on, but luckily there are some very nice Pentium 2 equipped Dell latitudes that have built in SB-16 compatible sound cards on a real ISA bus out there for pennies on the dollar which have kept me with an open option for DOS gaming on the go.

[nightrnr]

I wish I would have kept my 100mhz Pentium PC from back in the day. That system was PERFECT for Dos games; enough power to run almost anything Dos-related that I could throw at it.

But I learned a ton about PC's when I dismantled it and parted it out. I'd like to think it was a worthy sacrifice to the gods.

[Anapan]

Great to hear you found out the problem. There's some good old DOS gaming gonna happen! Make sure you put the Gollop bros' games on - X-Com & Magic and Mayhem. Actually, PM me about the games you decide for the final - I'm interested.
I'm currently trying to hunt one of these down:
https://www.youtube.com/watch?v=8T5jknGazmE

How cool would it be to play X-COM in Terminator/VirtualBoy mode?
Also It'd be stupid not to reflash a hacked BIOS to start up with "Cyber Dynamics Systems Corporation" and the Cyberdyne logo.

[Exhuminator]

LOL, no. I picked this stuff up to get away from the glitch-box that is DOS-BOX. I've had enough graphical maladies, wonky audio and games refusing to boot letting me know it wasn't worth using for any serious gameplay.

Well that sounds like the opposite experience I've had with DOSBox. No offense, but DOSBox is highly configurable and it's compatibility rests in the hands of the end user ultimately. All the same nothing beats the real thing, glad to hear you're having success with your true blue DOS endeavors.