Commodore C386SX-LT

Resources

Wiki – no wiki page exists for this machine
classicomputer.de

Please compare with Commodore C286-LT.

Internals

Motherboard

2MB Memory Module

Reverse-engineered schematic is available at my Github. This is a Mitsubishi MH1M16JS memory module.

LCD Screen

Sanyo LCM-5474

Backlight Power Inverter Module

Hard Drive

43MB Toshiba MK1122FC is HDD type 17 in BIOS.

Floppy Disk Drive

TEAC FD-335HF 063-U

LED Panel

Keyboard

BIOS

BIOS entry key combination is CTRL-ALT-ESC pressed after the system booted.

Power Supply

The original BIOS battery is AA-size 3.6V Lithium battery. It can be easily replaced with popular 1/2AA size 3.6V LiSOCl2 batteries.

The power supply is pretty unusual and hard to replace. The pinout is described on the picture below. My laptop had the capacitors on the power supply board leaked. This caused the voltage to the LCD screen go out of the original range and turning the contrast wheel to the maximum contrast level provided voltage that actually killed the portions of the LCD panel – hence the dark vertical line on it.

If there is no need to charge the battery, it is possible to connect only +12V voltage and ground pins, for example from a router power supply that was described on the Atari SF314 FDD page. The power plug is Mini DIN 6-pin and is generally available today to purchase.

Battery

My computer came with no battery. For information about battery and its replacements, please see post about Commodore C286-LT. It is exactly the same in both models.

Reassembly

21 thoughts on “Commodore C386SX-LT

  1. Hey Pawel, I just got my hands on the same machine. Mine is faulty, power supply sounds like it took a lighting hit. Do you have any schematics for it?

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  2. Are you able to draw pcb schematic of 2MB memory module? I ask because i would like to draw new pcb and i’m not sure where 2×2 gold pins are connected. Btw. It seems that power supply unit is faulty and cause malfunction of one of OKI M52998 chips – see distorted rectangle on the display. Double check capacitors and make sure that voltage levels are correct.

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  3. It would be great to get schematic of 2MB board. You’re right, i missed that part about the screen and leaked psu capacitors. I wrote about OKI chips because i fixed damaged panel some time ago by replacing faulty chips. In my case 3 chips were faulty, in your case probably only one chip is damaged and need to be replaced. OKI chips are available at aliexpress.

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  4. Wow that was very fast. Thank you. I will publish pcb when it’s done. Btw. Contact me (send an email) if you’re interested in fixing the display.

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    1. Hi Christian,
      To switch to external monitor you need to use DOS utility. I have it somewhere on the disk 😀 There is no other option to do that.

      I have got oryginal HDD but it is useless. To many not marked Bad Blocks…

      I used Compact Flash adapter with 2GB card and it is working perfectly. But you need to use EZ-DRIVE utility to prepare bootloader and format the Card. I also successfully tested SD adapter with 4GB card.

      I can prepare manual for both tools and share files.

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      1. Hi, I have recently acquired the ZEOS version of this laptop. Did you happen to find the utility to switch to external monitor? My machine currently has a dead backlight but otherwise in perfect working order. It would be nice to be able to actually use it with an external display until I can work out how to fix it properly.

        Regards

        Mike

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    2. Did you get anywhere with the PCB design? I was looking at having a go at putting one of these together myself as well

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    3. Hi Grzegorz

      Could you explain how did you replaced OKI chips. Im about to fix my display but in don’t know if it’s safe to use heat gun on PCB with lcd still attached to it on the other side or do I have to disassemble everything.

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  5. I have the same computer, but from Sanyo model MBC-18NB6h (the case and components are identical).

    I have a problem that every time I start up I get the message:

    “Invalid configuration information – please run setup program
    Press the F1 key to continue, F2 to run the setup utility”

    After entering the BIOS via the F2 key and saving the configuration I have the message each time:

    “SETUP has attempted to correct the following errors:

    * Standard CMOS checksum was invalid. Standard CMOS were loaded.
    * System configuration was invalid. Review the first page settings.”

    The CMOS battery is functional – the clock and calendar work.

    Does anyone know what the problem could be?

    Translated with http://www.DeepL.com/Translator (free version)

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  6. I ve got the schematics and service manual of the 286 version, but the 386sx is almost identical due to same chipset (for which i also have all informations…)

    I also did a lot of mods the last 30 years since i came across with this model first time working at sanyo (which is the real manufacturer of these units, commodore and Zeos are just OEM versions!)

    So it is possible to have up to 8 MB RAM instead of only 5MB (with some more effort also 16 MB( 15MB usable) is possible, but upper 8MB is SRAM then due to limitations of the chipset).

    There are different BIOS versions not only for the OEMs, but also between 286 and 386 models.

    It is possible to have a second COM: port with rather small effort the same like an external PS/2 Keyb.-Connector (working in parallel with the onboard keyboard!) and Networking, sound or even general PCMCIA can be integrated e.g. instead of internal Floppy-drive as there are all ISA-Signals available on the mainboard!

    The internal power-supply with leaking condensors should be repaired rather quickly to avoid damage on the LCD-Boards, that i can prove.

    Also the bulky external power supply gets faulty quite often, but is repair-friendly 🙂 if you know how switched power supplies work. Keep out of this box if not, it has dangerous voltages inside, even hours after disconnecting it from mains!!!

    I managed to get a quite modern “chinese” TFT running and mounted internally, but it takes the VGA analog signal, so it could be even more improved by modding the digital out (which at the moment is restricted to grayscale VGA panels…) But as 4:3 VGA/SVGA TFT panels get more and more rare, this is also not an long term option…

    The tools needed for switching between internal and external screen are from OAK and often are called “eagle” as this was the internal name of the VGA-chipset at that time… (i ve these tools too..)

    Currently i am working on a relaunch of my personal website, where i will place all that information and stuff, so at the moment please send private message for any question.

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