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Thread: $10 386/486 (Cyrix Cx486DLC installed + math co-processor) adventures

  1. #1
    Join Date
    Oct 2017
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    SE Michigan, USA
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    590

    Default $10 386/486 (Cyrix Cx486DLC installed + math co-processor) adventures

    Bought me another computer and this time a 386 system. It currently has a 1.44MB 3.5" FDD, 1.2MB 5.25" FDD, and some size IDE HDD installed along with a generic (possibly a WinBond chip) ISA I/O controller card and some VGA video card.

    Specs of the system:
    Unknown motherboard (will look for any markings to identify the board later on)
    Cyrix Cx486DLC CPU (either 33GP or 40GP)
    Math Co-Processor (might be a Cyrix Cx487DLC, will get a better photo)
    Board has 2 EISA slots, 5 ISA slots, has cache chips populated, 4 sticks of SIMM-30 installed, and a bad clock battery (will do a swap and check for any damage and if there's minimal damage, it'll be easy to fix and do a CR2032 battery swap, but I'll follow traces to install a diode to prevent the charging circuitry from blowing the battery up)

    The system itself was only $10 at a consignment shop close by, which $10 for a 386/486 system is actually a great price (better than eBay prices).

    Going to let the system set out for a while and do some more with it. My plans are to use it as a gaming system with 3 sound cards, plus a CD-ROM drive (proprietary one) to use it as a multimedia system and to play games that are overly speed sensitive for certain MIDI modules and games that were meant for 80386 machines. The Cyrix CPU is a 386 chip (PGA-132 LIF) with 486 instruction sets and 1KB cache.

    Stay tuned for further updates, adventures, and computer lab setup for my older systems.
    Current retro systems:
    Commodore 64 Breadbin 250407 Rev. C
    386/486DLC, Packard Bell Pack-Mate 28 Plus
    Toshiba Satellite Pro 410CDT, 2x IBM ThinkPad 380D (both TFT)
    iMac G3/600 Graphite, iMac G4/800 Lampshade
    YouTube channel: https://www.youtube.com/c/RetroPCUser

  2. #2
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    Oct 2017
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    SE Michigan, USA
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    The math co-processor is a CHiPs 387 and the CPU is a Cyrix Cx486DLC-33GP. Battery damage is minimal, so that'll be an easy cleanup and the innards, minus the battery are really clean.

  3. #3

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    Quote Originally Posted by retro-pc_user View Post
    The math co-processor is a CHiPs 387 and the CPU is a Cyrix Cx486DLC-33GP. Battery damage is minimal, so that'll be an easy cleanup and the innards, minus the battery are really clean.
    You got a fairly rare math coprocessor. C&T wasn't very popular because it was short lived.

    If you want to play speed sensitive games, DLC might not be the best choice. Maybe a standard 386-33 would be better.
    "Will the Highways on the internets become more few?"

    V'Ger XT

  4. #4
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    Oct 2017
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    Posts
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    SX or DX? And Intel or AMD?

  5. #5
    Join Date
    Oct 2017
    Location
    SE Michigan, USA
    Posts
    590

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    Ordered an Intel 386 DX-33 and swapped the 3.5" FDD and cable so that I could use the 3.5" as drive A instead of B. Need to figure out the schematics for this board so that I can solder a diode to the circuitry diode for the CMOS battery (already cut the original trace off from the positive terminal area to prevent shorts/explosions from occurring, but I'll verify to make sure again in case I done messed up). Funny thing is, the BIOS sees the 4.3GB HDD, but DOS begs to differ since LBA doesn't exist on a 386 board unless an enhanced IDE BIOS is used or XT-IDE Universal BIOS.
    Current retro systems:
    Commodore 64 Breadbin 250407 Rev. C
    386/486DLC, Packard Bell Pack-Mate 28 Plus
    Toshiba Satellite Pro 410CDT, 2x IBM ThinkPad 380D (both TFT)
    iMac G3/600 Graphite, iMac G4/800 Lampshade
    YouTube channel: https://www.youtube.com/c/RetroPCUser

  6. #6
    Join Date
    Oct 2017
    Location
    SE Michigan, USA
    Posts
    590

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    And the clock won't keep up. When I power it off, the time is 9 minutes behind (if I leave the system off for 9 minutes) or the settings disappear. I already checked the connections and they are all good.

  7. #7
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    May 2006
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    Quote Originally Posted by retro-pc_user View Post
    And the clock won't keep up. When I power it off, the time is 9 minutes behind (if I leave the system off for 9 minutes) or the settings disappear. I already checked the connections and they are all good.
    Symptomatic of low battery voltage to motherboard chip/s.

    CR2032 = 3 volts, then that will be reduced by the diode. Are you sure that is adequate for your motherboard ?

  8. #8
    Join Date
    Oct 2017
    Location
    SE Michigan, USA
    Posts
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    Yeah, the CR2032 wasn't sufficient enough. Apparently, the diode drops the voltage by 0.5V-0.58V, which is insufficient and the RTC requires 2.7V-4.5V exactly. I decided to solder a 3x AA battery pack by using a GameBoy DMG-01 rear chassis and the positive terminal from the mainboard of the DMG-01 since the board was dead anyway and soldered two wires: 1 for positive, 1 for negative and got 4.5V at the battery leads and 3.8V at the other end of the diode and to the RTC chip, plus, the capacitors and other points that are on the same circuitry. I soldered the battery pack to the external battery header since that is a safer method and I ran out of spare diodes from other boards that broke in the past.

    I then tested it out and the system is keeping the time, date, and settings. All in all, everything is working properly and I also changed the Sound Galaxy NX Pro H/W address to 240h so that the SAAYM (CMS/GameBlaster Clone + YM-2151 and YM-3012 Stereo DAC) can use the H/W address 220h. The only thing I need is to figure out how to disable the COM2 port so that I can use IRQ3 for the YM-2151 chip for a VGM player software so that I can play some VGM files.
    Current retro systems:
    Commodore 64 Breadbin 250407 Rev. C
    386/486DLC, Packard Bell Pack-Mate 28 Plus
    Toshiba Satellite Pro 410CDT, 2x IBM ThinkPad 380D (both TFT)
    iMac G3/600 Graphite, iMac G4/800 Lampshade
    YouTube channel: https://www.youtube.com/c/RetroPCUser

  9. #9
    Join Date
    Oct 2017
    Location
    SE Michigan, USA
    Posts
    590

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    Got COM2 disabled now, received an Intel i386 DX-33 and installed it, yet HIMEM test fails: says unreliable XMS memory at address 00113884. XMS driver not installed. With the Cyrix CPU, no error messages. The RAM itself has gold plated pins, yet the RAM slots are tin plated, which I believe is one of the issues, but I don't think that's the case. The system detects the CPU as an AMD Am386 DX-33 according to NSSI. So I'm not sure if it's because it want an AMD CPU installed or if it's something else I'm missing.

    I cannot find any jumper settings for the board, so I think it auto detects the CPU, so that shouldn't be an issue and the crystal clock oscillator is 66.67MHz, so it's the right speed.
    Current retro systems:
    Commodore 64 Breadbin 250407 Rev. C
    386/486DLC, Packard Bell Pack-Mate 28 Plus
    Toshiba Satellite Pro 410CDT, 2x IBM ThinkPad 380D (both TFT)
    iMac G3/600 Graphite, iMac G4/800 Lampshade
    YouTube channel: https://www.youtube.com/c/RetroPCUser

  10. #10
    Join Date
    Oct 2017
    Location
    SE Michigan, USA
    Posts
    590

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    I checked for bugs, and sure enough, there is a bug: POPAD bug: ! ERROR ! according to HWiNFO. No bugs in the Cyrix CPU, so maybe that explains the issue there. And there is a bug-free one (double-sigma ΣΣ) out there that I see (SX211 CPU ID marker). Going to order that CPU and some RAM to play it safe. Even MemTest86 won't load as the system restarts after showing the blue screen after the loading MemTest86 text appears.
    Current retro systems:
    Commodore 64 Breadbin 250407 Rev. C
    386/486DLC, Packard Bell Pack-Mate 28 Plus
    Toshiba Satellite Pro 410CDT, 2x IBM ThinkPad 380D (both TFT)
    iMac G3/600 Graphite, iMac G4/800 Lampshade
    YouTube channel: https://www.youtube.com/c/RetroPCUser

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