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Vanløse, Copenhagen, Denmark
Mathematician. Working programmer/system developer. Nerd. Married. Father of 3.


NMK Thunder Dragon Repair Log

I have to be honest...ever since I learned, that one of my favourite games Psychic5 was made by NMK for Jaleco, I have completely fallen in love with both companies. So I try to snap up as many games from both (when I find them at a fair price) as I can. Here I'd found an original NMK Thunder Dragon with "graphical errors" on evilBay with a starting price of 2EURO + 28EURO P&P. As I was the only bidder, I got it for the 30EURO all-in-all };-P.
When first booted up, the main intro logo, text layer and sprites looked fine, but some of the background layer was pretty messed up.

So dumped all socketed ROMs (they were fine) and did visual inspection. The board was in very fine physical condition, and the only suspective thing I found, was this

But they all checked out just fine using the continuity tester.
After having eliminated ROMs and physical damage, I had a hunch, that this error was caused by a RAM issue. So I started shortening adjacent data pins on the different RAMs on the board, to see if I could somehow stir up the graphics on screen. I found that the 4 MB84256 at positions IC1-IC4 is involved in generating the different layers on the screen. I googled the data sheet for MB84256-12 (that btw is produced by The Evil F aka Fujitsu) and found that they are just the Fujitsu equivalent of the standard 62256 with 120ns access time. These are not very common (at least not at the boards in my scrap pile), but at last I managed to find 2 pieces at 70ns and 85ns respectively and they both tested good in the Top2005+ };-P. So I tried piggy backing the 4 RAMs one at the time.

I saw a change when piggy backing the one at IC4.

So I desoldered it

and tested it in the Top.

So fitted a socket and installed one of the scrap-RAMs. Now the background layer was perfect again };-P

However it was now evident, that the game also had a sprite problem. I just didn't notice that before because of the issue with the backgrounds.

They all had stripes through them! So I tried piggy backing the 3 other RAMs, and on IC3 I saw a change in the stripe-pattern. So desoldered that IC as well

and tested it in the Top.

So fitted a socket and the 2nd scrap-RAM IC

and presto! All the sprites were back to normal };-P

So the two culprits are ready for the bin

and the case is closed.
The game is very addicting, fast paced, and has a very cool soundtrack. I'm really pleased to have it in my collection };-P


  1. Replies
    1. Thnx, Roy de Consolaz. Really respect your cudos };-P

  2. great writeup. it is always useful to learn a new trick or two.

    1. btw, what is that red/yellow wire coming out of your Top 2005+?

  3. @Alenor: That is part of an unfinished project, where I will use this cheap programmer to program 42pins 16bit EPROMs by the use of my own software u2Pa, an adaptor, and a small hardware hack on the programmer itself. The programmers ZIF-socket only has 40pins, so I need to "free up" some pins. So this wire is connected directly to the Vpp-supply inside the Top. That way I can draw that voltage without having to assign it a pin (I have tested this };-P)
    Note to self: Maby I ought to kick my self in the butt and wrap this up };-P

  4. aah yeah. i remember that post. i didnt realize you had routed the cable inside now.

    i considered getting the Top 2005+ just to try out some of your mods, but my
    GQ-4X handles most things i tossed at it OK.

    I do have to use this adapter
    for 16-bit eprom's but it works well enough.

    It doesn't do SRAM by default, but there seems to be a workaround that I am going to try before splurging on another programmer. Or i may just take a page from your book and try to do my own software for it, if i have the patience to document the protocol...

    either way, keep up the great repair logs. they make for interesting reading whenever I am in a techie mood.

    1. Thnx for the kind words. Glad somebody finds it interesting };-P

  5. I *love* your repair blog, even though I don't have anything to run PCBs at home.
    I come here every now and then to see what you've been up to and learn a few tricks (I always learn something when I come here). Keep up with what you do, I'm pretty sure I'm not the only one appreciative of your work ;)

    1. I'm honored *blush* Many thnx for the kind words };-P

    2. Elgen is loved by all ;)

    3. Ooooh, all that loving. Now I'm *blushing* again };-D