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Thread: NEC PC-8031 floppy power supply notes (part of PC-8001 computer)

  1. #1

    Default NEC PC-8031 floppy power supply notes (part of PC-8001 computer)


    Quick summary - no issues found powers up with all the expected voltages under load.

    I have a stack of 3 PC-8001 units all with the same power supply. I have never powered these units on, so I thought I would go through and check them over before doing so (as a faulty PSU can damage an otherwise perfectly good unit). I started with a PC-8031 (actually PC-8031BE for european 230V), the power supply unscrews quite easily, it is a BYG340/ 42K model made by Shindengen of Japan who are still going strong. I unscrewed the PSU (black painted metal case with vent holes), PCB was in good condition with no leaking / burnt components. Dated 1981. I checked over all the Elna brand electrolytic capacitors with an LCR meter, all measured fine as follows which is amazing for a 38 year old unit (must have been powered off for nearly all that time).

    Capacitors were marked and measured in circuit as follows (at 1kHz), all well within spec.

    C08-1 47uF 400V.
    C08-2 47uF 400V. In parallel with C08-1, measured 107uF 0.4 ohm.
    C13 100uF 25V
    C14 100uF 25V. Both measured 90uF 0.3ohm.
    C17 3300uF 10V
    C18-1 220uF 10V
    C18-2 2200uF 10V. C17/C18-1/C18-2 all in parallel, measured 11000uF.
    C19 2200uF 10V. Connected to above via filter coil and resistor, measured 18000uF. Measurement not stable, looked OK, didn't unsolder to do any accurate measurements.
    C20 470uF 25V. Measured 450uF 0.1 ohm.
    C21 100uF 25V. Measured 97uF.
    C22 1000uF 35V
    C23-1 1000uF 35V
    C23-2 1000uF 35V. C22/C23-1/C23-2 all in parallel, measured 3400uF.

    As above showed no issues I decided to power on at 230V with a 10ohm 10W load across the red/black output (see below for voltages). I didn't bother with variac or series light bulb (feeling brave).

    Powered on and no smoke / bangs, 12V measured across load so looked good. The output lead is to a multi-pin socket, the voltages measured on each pin were as follows:

    Black 0V
    Yellow +5V
    Pink +12V
    Blue -5V
    Red +12V (pink and red are commoned).

    So no issues with this PSU, a really well made unit! I will load up the 5V output too as a test first before connecting it to the PCB but I don't expect any problems.

    I will check out the hopefully identical PSUs in my other two similar units (PC8012 and PC-8032) and report back any differences. I'll start a new thread on the PC-8031 PCB and drives, the PCB in this unit contains a FDC chip and some RAM plus some dreaded tantalum capacitors so plenty to look into.

    Here's my webpage on the system:


  2. #2


    One of my PC-8031 units were repaired long ago, I remember having only two issues, a shorted tantalum capacitor in the 12V rail and a badlogic IC, I can't remember the exact one, a LS357 comes to my mind. Apart from this, these units are indeed pretty robust, perhaps a little bulky.
    One of them have now a 3.5" drive, much easier to work with when sharing software with my PC

  3. #3


    The 8031 is a huge addition to the already fairly large PC-8001. I'm glad my 8801mkII has internal floppies

    It looks as though the 8031 will happily work with the PC-6001mkII's external floppy connector (and maybe the 6001 floppy cartridge) as well:

    Thanks for the writeup!

  4. #4


    Yep, it's just a matter of build the right cable and it works

    The evolution to a more compact unit is the PC-80S31, a really nice disk drives set.


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