EDIT: Striking out stuff that was not seen in a previous reply while I was typing
Well isn't this a wonderful coincidence! Greetings! I'm also new here. Long time lurker over the years but finally in my second or third wave of nostalgia and decided to sign up. I have the exact same system as you. I'm planning on doing a post when it's complete or almost complete mostly on what I've learned and to keep track of bits of info that I've learned all over the web about these systems. Looks like now is as good a time as any to put it out there.
(Apologies in advance as this is going to be long. Also, if the images are offensively large, I'll figure out how to shrink them down and edit this post)
First, I can't believe you managed to find a system with the monitor and keyboard! They look great! I went for a Dell 486 this time around because I think they've aged really well compared to other computers of the era and the compact size is appealing. The original mouse would probably have been a 2 button Logitech (Dell branded on the face) PS/2 mouse that's quite uncomfortable to use. They were very common until the Mouse 2.0 then later Intellimouse came along from Microsoft with Win95. Sorry, I just tossed an incredibly yellow but functioning Logitech one. Anyway, my story is I bought a dead but excellent cosmetic looking 433s/l. Bad PSU and a bad capacitor controlling the RTC pulse (clock was dead). Before I fully fixed the RTC, I bought a spare motherboard (that happened to be the newer revision). The component layout and PCB traces are significantly different for some reason.
I was finding conflicting info on this system until I realised that there are two different motherboards in the same case (as I said above). At some point in time they added the word Optiplex to the badge on the front (or it was there depending on the way the machine was sold new. I don't know really) but from the images I've seen trawling the internet, the board revisions don't necessarily coincide with the word Optiplex appearing on the case. Either way, they always identify as Dell System 4xx/x on the POST screen.
I'm going to photo/info dump some info for you that hopefully you can use to help you in your quest! The video upgrades appear from time to time on places like eBay but they are expensive because people know they are rare. Be careful though as for some reason Dell changed the size and pinout on these between models/revisions even if they all use the exact same specced and pin count of RAM chips on them. I'll give info on both revisions even though I'm fairly certain you have the earlier one based on the cache upgrade diagram but having info on the later type will help you avoid parts that say they are compatible even though they aren't. Dell really loved proprietary in the 90s!
***Older type board***
*Latest BIOS version is A17
*BIOS shadowing can be turned off
*Headland HT340 chipset
*5V CPUs only
*CPUs tested and working: i486 DX 33, i486 DX2 66, i486 DX4 100 ODPR (Reports in BIOS as 33MHz but operates correctly at 100MHz), Cyrix DX2 66 (oddly it reports as a DX4 100 in the BIOS but is operating at 66MHz), Kingston Turbochip (AMD 5x86 133MHz) (Reports as 33MHz in bios but operates at the correct speed)
*16-bit ISA riser option only. Comes in 3 or 5 ports depending on the case size. No VLB riser add-on option.
*Interestingly has an FSB jumper for 16MHz which works and could be handy for slowing down the system (if you really needed to for certain games/programs).
*40MHz FSB jumper does not function. No video, system does not POST. I suspect the VLB integrated video doesn't like it.
*EDO RAM will work(ish). Only one EDO SIMM is possible and some crash immediately. I got one 16MB stick to boot and into CACHECHK. Speed was identical to using FPM RAM. I did it for science, nothing more. Don't recommend this.
*8MB FPM SIMMs don't appear to work for me. I didn't except it to but I tried some old Mac RAM (It functions fine on a Pentium board I have)
*64MB RAM max tested
*128kB cache is the only option for cache on the proprietary board. Dell Part# 29517 (first Google image result will show you it. I'd post it but it's watermarked) The motherboard has a male pin array connector and the board site flat (parallel to the motherboard). This cache board is an odd one. It uses some sort of cache controller and none of the chips look like regular SRAM chips. I'm just speculating but I would guess this motherboard's chipset is in fact a souped-up cacheless 386 design that requires an additional controller in order to use cache.
*Tseng ET4000/W32 VLB video w/ 512kB RAM (additional 512kB possible with proprietary add-on board)
*No onboard PC speaker
This is the video board you're looking for. I don't see any actual part number though. Annoyingly there are a multitude of different video upgrade boards for Dell 486 systems. The System 486p with Cirrus Logic video also uses 4x60ns chips for an additional 512kB but is different and incompatible.
As for CPU upgrades, you can buy an ODP labelled CPU and drop it right in the LIF socket to disable the SX or you could just wire bodge like I did to disable it and use any 5V CPU including Intel ODPR models.
***Newer type board***
*Same specs as above with some minor differences.
*Intel DX4 reports correct speed
*Lowest FSB jumper is for 20MHz (works) and highest is 40MHz or RESERVED. Both of these just boot the system at 20MHz FSB
*Latest BIOS version is A13. Here's the odd part, Dell lists both these boards as one system and has the same BIOS update. The version reports differently depending on which board you've flashed.
*BIOS shadowing cannot be turned off (unlike older board)
*Riser is completely different but occupies the exact same space.
*Additional/optional VLB riser can be used in conjunction with the standard ISA riser
*Cache option is the same HT44 controlled 128kB of asynchronous cache but in a completely different form factor. Dell Part# 39077. It occupies the VLB riser slot (or a VLB slot on the riser) in addition to a little extra edge connector labelled "cache". It stands perpendicular to the motherboard.
*CPU upgrade jumper is present meaning you most likely don't have to wire bodge if you have an SX soldered on.
*5V only CPUs in Socket 3 (thankfully!)
*Soldered on PC speaker but unpopulated header for external speaker
* 512kB or 1MB standard video memory on board in 4 or 8 chips respectively and yet another upgrade board for an additional 1Mb. Doubt I'll ever track this down.
Ok and now for some random facts and other bits that didn't fit in above
*Keep the VLB video. The ET4000/W32 is fast in DOS and windows accelerated. 512kB won't matter in DOS or if you want to run Windows in 800x600 256 colours. These chips apparently have some sort of interleaving (so I've read on this forum elsewhere) if they are setup with 2MB and it's only really effective in Windows.
*If for whatever reason you need to upgrade/replace the hard drive you can:
A: Use a dynamic disk overlay (I had a 12GB Seagate drive I used with one and didn't notice any slowdown. It also worked fine in an external USB drive enclosure).
B: IDE to CF card (no idea if DOO works with these to be honest)
C: XT-IDE BIOS in something like a network card. I can confirm this works great. Note though that you have to set both drive types as NONE in the BIOS and turn off "Report keyboard errors". You're going to have to permanently deal with "Hard Drive Configuration Error" but disabling the report keyboard errors means you won't get 2 beeps and have to press F2 to continue.
D: ISA SCSI
*Memory speeds are just meh from this BIOS. I happen to have 60ns RAM in mine and both boards report a memory speed in CACHECHK at 32.8MB/s with a DX4 100. It's pretty much set up for 80ns RAM unfortunately. I'm interested to try out an earlier suggestion on this post though with that DOS utility.
*L2 cache speeds are pretty tight. That's the one good thing about the proprietary board I guess. Good luck finding the board. I never could for the older revision board. The newer type that is like a VLB card is much easier to find and must have been used in more systems and for longer.
*The case and riser cage are slightly different between boards but they both fit with some minor trimming if you need to swap (I put in the newer board because I wanted L2 cache and maybe someday a VLB riser etc)
*If you haven't already, you can use a 3xAA battery holder and wire it up from CMOS. Works great and much easier to change in the future.
*THE BIGGEST PROBLEM!!! - Electrolytic capcitors
I cannot stress this enough. These boards use an inordinate amount of electrolytics and they are not good it seems. The earlier old logo Dell systems 386 and 486p use none! Even later systems like their P MMX and PIII systems don't use that much. These are up there in my experience with early all-in-one Macs, Mac II.
The older revision board appeared to only have one capacitor visibly bad. This caused the RTC to not tick tock. Replacing it and cleaning up the residue restored its function but the clock was erratic. Turns out the RTC's 32.768KHz crystal needed to be changed. It appeared to work perfectly after that except no fast CPU would POST. DX4 ODP and ODPR as well as the Kingston Turbochip wouldn't work. I initially figured it was some sort of BIOS limitation from Dell. Re-capping the entire board completely fixed this.
The newer board had fuzzy video so I knew it needed a re-cap. It looked completely clean though on the surface. Interestingly, the Intel DX2 would randomly post and crash/throw memory errors or not POST at all. Cyrix DX2 was perfectly stable. Neither fast chip worked. Again, re-cap and all is good.
Between both boards, only one capacitor was visibly leaking and none were bulging. Having replaced them, on the old board ~33% were actually leaking and on the new board ~75% had leaked. I really advise you to either do this or find someone who can do it for you! I cannot stress enough how shocked I was by this. I know it's a sample size of only two but I've never seen anything like this except for old Macs. The old board appeared to be functioning perfectly other than no DX4 functioning.
Again, sorry for the length. Don't want to hijack your thread but figured I'd give you everything I've learned since I started with this machine two months ago.
