So you might be wondering why I’m running a q-tip over this 486 logic board. After all,
NCommander, don’t you mostly work with software? Well, yes, but this system was given to me
by a friend, and represents my first attempts at hardware restoration and vintage data recovery.
Now I do want to mention this advance that I did make some mistakes in this project,
so this video serves both as an overview of my efforts, and also a warning of what not
to do, and what I should have done in hindsight. At the risk of spoilers, I will note that
this system, as of writing, is partially working and I didn’t cause any permanent damage.
Let’s backtrack a bit. This is the system as I got it originally, and it’s an Intel
Professional Workstation 486, a pizza box type desktop computer with surprisingly high
end equipment for it’s era. There isn’t a lot of information online about these systems,
but Intel seems to have sold them from 1991 to 1993.
While Intel is primarily known for making processors, they did have a small line of
computers for sale which were essentially a combination of both reference platforms
and speciality hardware. This becomes pretty clear when we flip it around to the back.
I’ll let past me explain in detail.
Alright, let's take a look at the back of this machine and we see what we have working
because there are some unusual things about this machine
Here on the back, we've got two serial ports, a parallel port, and then unusually, we have a SCSI adapter
which is not typically found on most pizzabox or low end machines
so this suggests that this is some sorta workstation machine
Then we got two PS/2 ports, a VGA adapter, integrated Ethernet, and an AUI adapter.
Obviously a sound card of some sort has been added, and we have an empty slot here
So opening the system up, there are more things inside.
The top basically just slides off ...
With the case off, we can see some more oddities. Inside this metal caddy, we can see both the
floppy drive, and the hard drive made by Digital. Given what we already saw on the back, it
should be unsurprising that this is a SCSI hard drive.
To the left, we have the card slots sitting off this riser board. It may not be clear
from the video, but these are EISA slots. For those not familiar, EISA, standing for
Extended ISA, was a backwards compatible extension to the original ISA slots found in early PCs.
EISA was mostly created as a response to IBM patenting their Microchannel Architecture,
but both were relatively rare even in the era. In general, EISA slots were only found
in server and workstation computers.
Past me is going to keep disassembling the system to look for problems, but eagle eye
viewers might have noticed one right off the bat: this system has a Dallas Time Chip. I’ll
talk about why these are a problem later, but Dallas chips are notorious for failing
for one simple reason: they have an integrated battery which can’t be trivially replaced.
These things are a giant pain, but thankfully, this specific chip is already socketed so
I won’t need to break out the soldering iron.
The next headache is this non-standard power supply unit. It just sorta slots against the
main board, and it has a 20 pin connector. That doesn’t correspond to any of the standard
PC PSU connectors that I’m aware of. As I would find out, this power supply is pretty
much unique to this system, but I’m getting ahead of myself.
This is a good time to talk about why I have this system. Originally, I needed a system
of this vintage to help test Banyan VINES 5.0, and to resolve an issue I was having
in reverse engineering and bypassing its copy protection dongles. My friend said I could
have this 486 on the condition I dump the hard drive for him. Unfortunately, this specific
machine can’t accept a 5 ¼ inch drive, so it’s useless for my VINES work. That
being said, I still wanted to help my friend, and I found the system itself was interesting
enough to document.
To be honest, I’m really not much of a hardware guy. While I do know how to solder, I’ll
fully admit that I’m definitely out of my wheelhouse with this project. That being said,
a large part of vintage computing involves the hardware part, so I figured I should learn.
With the mainboard out, it was time to inspect it for leaking caps and other damages. It's
hard to see it on camera, but there’s a fine layer of muck coating everything, and
frankly, I want to clean this board thoroughly before attempting power on. I know other people
have had success with running things through a dishwasher, but I’m not really comfortable
with that. This board has factory-installed bodge wires, and I felt a more delicate touch
is called for.
There’s nothing left to do but some elbow grease into it, so lets cue the music and
break out the time lapse!
Ok, that took awhile, but totally worth it!
After that through cleaning and examination, I’m happy to say that I didn’t find any
bulging or leaking capacitors so I’m reasonably confident that this is safe to power up. That
being said, I felt like checking the PSU was a prudent move before going further.
Before I go into what I found, I’m going to prefix this with a warning. If you don’t
know what you’re doing, you should never open up and work on a power supply unit. Mains
voltage is not something to mess around with, and capacitors can retain a charge for an
extended period even if disconnected.
With that disclaimer aside, let's get to it. Just from examination, I can tell someone
else has been in here: there are screws missing. Beyond that though, it didn’t take too much
to disassemble the PSU. My first surprise was the PC speaker flopping around when I
opened the case.
In truth, the speaker is actually bolted by a screw on the exterior shell, but this wasn’t
evident at first. Frankly though, the whole thing left me flabbergasted: I’ve never
seen a PC speaker inside a PSU, and I can’t imagine what drove this design decision. It’s
not like there isn’t room in the main case!
Even when properly mounted, the speaker sits very close to an unshielded inductor. It wouldn’t
take much to cause this whole thing to short out. Beyond that, this PSU is very tightly
packed; there are plastic inserts to prevent components from touching. I just got the
feeling that this wasn't a well designed piece of hardware. The only relief I saw is there
is a fuse to protect against catastrophic failure, and a lack of RIFA capacitors.
The entire PSU was caked with dust and grim, so I spent more time and effort getting all
the crud out of it. In truth, I would have liked to remove the case entirely, and I did
disassemble most of the PSU in an attempt to do so but I ran into a major problem. Because
of how tightly packed the PSU was, to take the main board out, I would have to remove
the plug mounts. In theory, that should have been straight forward if they weren’t held
in place with two stripped screws in an awkward location.
Despite my best efforts, I couldn’t get the screw to release, and given their condition
I suspect it will take some serious effort to get them out. I’ll reach out to the Vintage
Computer Forum and other experts and see if I can get any good advice on how to remove
them. The good news is that all the capacitors, as best I can tell, were in good condition,
and I didn’t see any leakage.
Given that this power supply had a proper fuse, I was reasonably confident that even
in the case of a cap fails and shorts, it wasn’t going to fry the logic board. My
thought process is that if the PSU dies, it’s likely safer and saner to rig an adapter to
a modern power supply than rehabilitate this one.
If you’ve got any good advice on either the stripped screws, or how to handle a potential
PSU replacement, I’d like to hear them below. At this point though, it's time to reassemble,
and it's where I made a nearly critical mistake.
At the top of the PSU, there are three connectors for where the PC speaker, and the two case
fans attach. During my aborted attempt at disassembly, I had disconnected these wires
from the main circuit board, and rather stupidly, I didn’t take a picture or properly mark
them, nor were there any markings on the board to say which was which.
This was a real problem because some fans run on AC main voltage, and I was certain
to blow something up if that was the case, and since I couldn’t remove the main board,
I couldn’t follow traces to know for sure. Furthermore, I wasn’t going to try to connect
a multimeter to the inside of a live PSU to measure voltages.
Let this be a listen to any would-be restorer, be careful to mark and document how things
come apart if you have any intention of putting them back together again! For future projects,
I’m going to make sure I take a lot of dedicated still photos and attach labels to prevent
this from happening again.
I was slightly panicked due to this SNAFU, but then I got a lucky break. Upon a close
examination, I noticed that there was a label through PSU grills, and I could just make
out the words “12 VDC” on one of the fans. That told me that these were DC powered fans
and not AC. If that was the case, a misconnection wasn’t necessarily catastrophic.
In hindsight, the smart thing would have been to simply connect the fans first one by one,
and use that to determine the proper connection. That way, I wouldn’t have risked accidentally
blowing out the PC speaker though overvoltage.
What I ended up doing was simply taking a guess, and hoping the fuse and the fans would
prevent a catastrophic short circuit. I will fully admit I could have done better here,
but this entire project has been a learning experience to say the least. With the PSU
reassembled, it was time for a smoke test.
*CLICK*
* audible whining noise from PSU*
That ain't right ...
That's defiantly not right ...
*PSU turned off - buzzing noise wobbles away*
Well the good news was there wasn’t a popping noise, fire, or the distinct odor of magic
smoke. The whining sound was being caused by the fan voltage being sent to the PC speaker.
In truth, I had trouble hearing it, and thought it was one of the fans grinding before I realized
what had happened. I ended up bleeding the PSU capacitors, and swapping the leads around
which solved the issue.
At this point, I would have liked to measure the voltages coming out of the PSU, but it
seemed like a really bad idea to jab multimeter leads into the PSU sockets blindly. Past-me
is going to start reassembling the system, and while we do so, I’m going to talk about
another hindsight moment.
Without a schematic, I can’t definitively say what each PSU pin provided what, but there
was a way I could have determined both ground and the DC voltages without risk to myself.
PCs generally run on a combination of positive and negative 5 and 12 volts, and there are
several points on the board where I know I should be able to find those voltages such
as at the card slots. Armed with that knowledge, I could potentially have reversed engineered
the power pinout.
Regardless, with the reassembly complete, it was time for a proper smoke test. I’ve
moved the system to my desk, and I’m using this modern LCD as a display since it has
a VGA input. For this first try, I’m leaving the disk caddy disconnected since if the system
blows, at least the hard disk will survive.
Here goes nothing!
Past Me:Well, time for a smoke test ...
Well, it didn’t explode, which is what I’ll call a win given everything up to this point.
As expected, we get a POST code about the real time clock being dead, and then the system
hangs trying to initialize the SCSI bus. This is entirely expected since the bus isn’t
terminated, so it’s time to put the disk caddy in, and see if it boots.
That was a somewhat better result, but quickly becomes clear that this system isn’t healthy.
First off, we get a new error message that the EISA configuration is invalid, followed
by DOS hanging when HIMEM tries to test extended memory. By pressing F8 on startup and skipping
HIMEM and AUTOEXEC.BAT, I managed to get dumped to a C prompt.
I was a little concerned about the memory test hang, although I did find it rather strange
that the BIOS memory test passed, while the DOS based one failed. It wasn’t something
I was going to immediately concern myself with though since my first goal was to dump
the filesystem in some form.
My big hope here was that given this system had on-board Ethernet, there was a good chance
that there some form of networking software installed, and it was here I struck paydirt:
NetWare’s ODI client was present. Given my prior NetWare experiences, this seemed
like a quick and easy solution to getting the files out.
Unfortunately, the LP486E driver wouldn’t load, complaining of invalid configuration.
We already knew we had a problem here, so it was time to solve it. I have never owned
or used an EISA system before, so I didn’t know what to expect, but the first place I
thought to look was in the SETUP screens. There, I could see options relating to the
onboard LAN controller, but none of the changes I made would persist across a reboot. I’ve
already alluded to the cause, but it’s at this point we need to loop back to the Dallas
time chip I talked about earlier.
Beside providing a real time clock, the Dallas chip also provides a small amount of persistent
storage, approximately 50 bytes worth, which can be used to save system settings. With
the chip’s built-in battery dead as a doornail, the system can’t save its configuration.
The specific Dallas chip in this system, the DS1287 is no longer manufactured, and the
odds are that any I got off eBay would also have dead batteries.
There are two known solutions to this problem. The first is using a dremel to carefully cut
the sides of the chip and attach a replacement battery. To be honest, I’m not exactly thrilled
at the idea of doing this, so this option is what I would call a last resort.
The second is to use a modern replacement. Maxim Integrated makes the DS12887+, which
is supposedly a drop-in replacement for the DS1287. While researching this, I’ve seen
somewhat differing reports of success on replacing the Dallas chips with more modern parts. Still, at $10
dollars each, they’re cheap enough to take a chance on, so I’ve ordered two replacements
from DigiKey.
Beyond that, I’ve also ordered a few odds and ends to help me dump the filesystem even
if I can’t further go than this. To be honest, I actually did a lot more experimentation
with this system even after hitting this stumbling block, but we’re out of time on this video.
If you want to continue to follow my computing adventures, do me a favor, leave a like and
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I can be found on Twitter and Discord if you want to follow my adventures in real time.
Until the next time, this is NCommander, signing off.