EUROPEAN DRAGON'S LAIR/SPACE ACE SOFTWARE CORNER LASERDISC MODIFICATION - 28 November 2007 | 7 February 2010
Developed by Jeff Kulczycki, written by Matteo Marioni, with contributions by Shaun Wood

INTRODUCTION

This ROM modification allows the laserdiscs reprinted for the Software Corner home system to be used in European Dragon's Lair and Space Ace arcade games, which use laserdiscs and players manufactured by Philips in PAL video format.  Apart from the laserdisc players being VERY unreliable, the laserdiscs are almost all gone for good due to the laser rot issue.  So, if you still have a European Dragon's Lair or Space Ace with a working laserdisc player, you most probably need a replacement disc in order to have a good video display.  One solution is to use the discs reprinted in the early '90s for the Software Corner LDG home system, which are PAL copies of the original Philips discs, except these discs have a frame offset and are not directly interchangeable with the arcade discs, hence this ROM modification.
You need a true Software Corner reprinted disc, not one of the early Software Corner discs which are just original Philips arcade discs with a changed hub label.

Reprinted discs look like this :

Early Software Corner discs look like this :

So please be careful, because these early discs are just 1983 arcade discs with a new label, and most of them will suffer from laser rot.

Note about Space Ace :  Software Corner Space Ace laserdiscs have digital audio only, and they are not compatible with the original Philips 22VP932 laserdisc player used in the arcade games, as the player is not capable of playing digital audio.  So, to use a Software Corner laserdisc in a European Space Ace, you must also replace the player.  Consider the various Laserdisc Player Conversion Products, or doing the EuroDL PC conversion.

PARTS NEEDED

• Modified ROM image (see download section)
• One or more blank 2764 EPROM(s)
• EPROM burner

THEORY OF OPERATION

The reprinted Software Corner discs differ from the original Philips discs by an offset of 78 frames.  For Dragon's Lair discs, 78 needs subtracted from the frame value for each search the arcade game poerforms.  By disassembling the ROMs, Jeff saw that every frame search in the game is calculated on a 00000 base offset, stored in the U45 ROM.  Jeff changed it to 99922 (78 frames less), and now the game works perfectly using a reprinted Software Corner disc.  This modification has been done for the three known (so far) European versions of the game :  Atari Rev.D1, Atari Rev.D2, and Sidam.  Shaun did the same for Space Ace, for which the offset is positive, so he changed the base offset to 00078 in the Space Ace U45 ROM.  The new ROM images are in the download section below.  Shaun also updated the CRC inside the ROMs to have them all pass the CRC test performed at boot.

You can view Jeff's work in the disassembled and commented code for the Italian version of Dragon's Lair in the .asm file contained in the zip archive.

CONSTRUCTION

Simply burn one of the included U45 ROM images onto a 2764 EPROM, and plug it into U45 located in the right-center of the European Dragon's Lair or Space Ace board.

DOWNLOAD

Documentation is included in the download in the form of a readme.txt file.

    DOWNLOAD  Euro_DL_SA_Software_Corner_Disc_Mod.zip  NOW!

DISCLAIMER

The above is believed to be correct and works fine for the authors.  No one is forcing you to do this.  If you break your game, it's your fault!

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