Desk486

Author: Devon
Date: December 1, 2024

category: “Retro Rebuilds”
tags: refurbishing, rebuilding, upgrading, renew, upcycling…

(RE-)BUILD LOG for (UNNAMED) DESKTOP 486

working name: Other486

ORIGINAL HARDWARE

  • Desktop-style AT case, manufacturer unknown. Drive cage is stamped with “???”, front bezel also has this acronym molded in. Haven’t removed the board yet
  • Front bezel has no badge, stickers or markings of any kind. There is a “Made in USA” sticker on the underside of the case.
  • Rectangular green power and (IDE? just HDD?) LEDs. No Turbo LED.
  • 4-prong AT-style mechanical power switch, momentary reset button, no Turbo switch.
  • Vented portion of front bezel can be removed without removing the panel or opening the case,
    and there is a dust filter behind it.
  • 3x External 5.25″ bays, 1x External 3.5″ bay, 1x Internal, with tabs for mounting a PC speaker. The speaker is instead mounted in the front bezel (suggesting this cage was likely used in other case models whose bezel lacked a speaker mounting position.)

??? brand AT Power Supply (read on), Model: USA-300

MSI MS-4144 v2.?? motherboard:
Socket 3, SiS 496/497 chipset (Rev. B4: 85C496NV + 85C497NU),
4x 72-pin SIMM slots, 3x PCI, 4x ISA.
CPU voltage regulator, board has space for a second adjacent. Not heatsinked or
affixed to the board (I suspect this regulator has low heat output.)1
RAM: (1) stick of 4 MB RAM, PCB marked “MADE IN JAPAN”, “ADSIM”, “Q232-02”.
Back reads: “TEXAS INSTRUMENTS”, “ASSY IN JAPAN”, “Z124BBK32”, “-60 A 9502A”.
Chips’ markings not readable. All chips have a sticker reading “TURBO”, except the
ones at either end which read “4MEG” and “45NS”.

Cyrix 5×86-120 CPU, with aftermarket PC Power & Cooling HSF

ORIGINAL SYSTEM CONDITION:

  • PSU shows signs of repair.
  • Fan filter did its job well, was thoroughly clogged and the interior largely dust-free, with the exception of the drive cages. My guess: negative pressure from the PSU intake behind the 5.25″ cage pulled dust in through the spaces around the drive bezels.

ODDITIES

  • SiS 85C496 has a sticker reading “HSB Technologies” which would be a perfect fit on the front bezel,
    in the space where a badge would go. I would guess for cooling, but I’ve never seen this part heatsinked.

POWER SUPPLY

The PSU may need repair/replacement. It powers the machine fine (VOLTAGE TESTING PENDING!), however the short circuit protection failed to trip during an unscheduled test involving +5V and ground.


I need to open the PSU to see what that is about. Without opening it up, there is evidence the PSU was at some point repaired: a curious sleeved power lead for the fan runs out of the PSU to +12V/GND at a molex connector, and the tamper-evident sticker on the PSU is broken.


Possible replacements on hand:

  • Delta Electronics (MODEL #? 300W-ish)
  • Enermax Noisekiller (MODEL #? 400W-ish)
  • EVGA 650 G5 Gold
    • (not suitable because the modular connectors are where the original PSU has air intake vents, and its fan intake would face the bottom of the case with nearly no clearance. It could be installed upside-down with new mounting holes drilled in the case, but I think an SFX supply with adapter would be a more elegant solution and not require modding the case.)

Researching:


6 pin jumper block replacing resistor network “JC3”: replaced with jumper block in this board revision. I assume MSI added some resistors to the PCB for this arguably more convenient jumper block. The pads from the old “JC3” resistor network are left over.