tgwave

Hello Simius, Would you kindly put me down for 2 standard boards.

Your 800XL has BASIC built in. It acts like a cartridge. To disable BASIC, hold down the OPTION key while turning the power on. I expect this will solve the issue with those games that show a blank screen or random garbage characters.

I have just stumbled on this presentation myself. I watched it on YouTube at this link: http://www.youtube.com/watch?v=K5miMbqYB4E The gentlemen at Visaul6502.org have discovered that the illegal opcodes LAX (simultaneous LDA, LDX) and SAX (simultaneous STA, STX) are indeed built into the silicon. Fast forward to time counter 44:45 for the subject on illegal opcodes.

Some months ago I found an excellent web-site relating to circuit board repairs and modifications. Follow the link below: http://www.circuitrework.com/guides/guides.shtml Point your mouse pointer at the 'Guide Book' tab and select the index to one of the nine chapters. The information on these pages have been prepared by seasoned professionals.

It does sound more like a hardware (cartridge) fault in your case. Be aware that PROMS are more than just a collection of stored data. There are input address address lines which select the approprate position in the "array" of data. There are also data lines which produce the data to the CPU/ANTIC chips. These data lines are controlled by an "enable chip" pin on the PROM. When the PROM is not being accessed these same data lines go high impedance to allow other devices to use the data lines. It is feasible that the PROM access management circuitry is damaged (not necessarily complete failure) but the data remains intact. I know this does not explain why the cartridge worked on other model Atari's. Without delving into the enormous topic of semiconductors, perhaps the 600XL with your "ISA" memory chips in combination with a PROM/cartridge are affecting the voltage levels on the bus. Or on a simpler level, is the 5 volt supply line being loaded down when a problem cartridge is inserted? There are so many variables. This weirdo problem you are having may be beyond the scope of advice by remote. A visit to your local electronics tech' may be useful!? It in fact crashed the XEGS when executing the code. I did not investigate exactly what was going on in the XEGS. My theory is based on the assumption that the custom MMU is the same as in the 130XE. RAM at $4000 to $5FFF was being switched out and due to absence of expanded memory there was a void left.

I must agree that this sounds like a RAM problem. Selective cartridge failure can be attributed to how that cart program operates when there is an absence of RAM after $3FFF. My first Atari was a 600XL with the memory expander module (back in 1985). After a number of years of use and transporting I would occasionally encounter a bad connection between the computer and module. This resulted in the absence of the extra RAM. Regardless of the type of memory upgrade you have, suggest using the in-built self test function (hold down option at powerup, no cartridges) and select the memory test. This will let you know if your memory upgrade is letting you down. Note that if you enter the self test mode from basic by typing 'BYE' you will never see 48k of ram since the basic rom is occupying the last 8 kilobytes. As an aside, there is a disk that PAGE 6 magazine used to sell containing some digitized music demos. This disk did not work on my XEGS. At first I suspected the XEGS and examined the circuitry intently but subsequently could not fault. It then occurred to me that the XEGS was not necessarily 100% hardware compatible with an XL. I tried the disk with my XL and it worked fine. After examining the machine code I discovered that the author had skipped convention when using register $D301 for bank switching. Instead of loading the register and then manipulating the appropriate bit(s), the author loaded the accumulator with a specific byte and stored it into $D301. From memory there was one or two bits set to zero that should have been set to on. Moral of the story is to question the premise of your conclusions! I was so close to dismantling my XEGS.

tgwave/A18B5 081880/Taiwan/A18A1 198260/880125/PAL Australia Looking inside the keyboard case I found the text "MADE IN JAPAN" to the left of the space bar. The part number "C070015-003" is to the right of the spacebar. Both texts are part of the moulded plastic plane on which the keys are mounted on. Perhaps all keyboard innards were manufactured in Japan.