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davemac

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  1. davemac
    Done! Thanks, Dave
  2. davemac
    Hello, My 400 is a UK PAL model with serial BY 110920. It looks to be a late '81 model. Thanks, Dave.
  3. davemac
    That's great! I decided to try it on my 400 tonight, and it works fine. Ironically, my 800 seems to have been done that year too! Sadly the 800 broke last week. It now needs a C015199 ROM and I think a bad 7805 regulator caused it. I'm getting a 6V output from it, which is very odd. I've heard that you can program your own ROMs as they were based on the 24C64 EPROM/PROM. It's early days yet.
  4. davemac
    Hi everyone, Sorry to bring up such an old thread, but I bought an 800 back in the late 80's and the previous owner had managed to effectively build a Pill switch into the machine itself. It is just a NAND gate, which connects the R/W line (R line of cart slot) via the gate to cart slot pins A & 14, presumably to change the base address. The in-line two-way double-pole switch sits between the 7400 chip and the cartridge slot's pins. If anyone would like to build one I'll sketch up a schematic. Cheers, Dave
  5. davemac
    Hi everyone, Success at last! I thought I'd tried everything, but I was wrong. The wiring shown below is correct for the Mapsoft board. Thanks to the ex-Maplin man for remembering the four wire modification, and the very technical information from some clearly very knowledgable people. I replaced all RAM ICs for 4164s earlier just in case, so that may have helped. Again, thank you all for your input. I was amazed as to how much help I've received on here. Dave.
  6. davemac
    Hi.Thank you for your post. I tried reversing M & T, but left N & R in their current config initially. Next I reversed N & R and tried M & T reversed and normal, so that's the remaining three combinations. I'm assuming that's what you meant, but I'm not 100% sure. I'm guessing that N & R were probably already correct because both 74LS42 ICs (RAM board and motherboard) have pins 13 & 14 commoned, thus connecting A14 and A15 to both of these address decoders? Thanks again, Dave.
  7. davemac
    Thanks everyone once again. I discovered that RAM slot Pins M and T have 1K resistances to ground, so, assuming they are RD4 & RD5, I have connected everything as below: RAM slot Pin M to Pin A of cartridge slot (RD4). RAM slot Pin T to Pin 14 of cartridge slot (RD5). RAM slot Pin N to Pin 13 of 74LS42 (A15) sorry about earlier typo! RAM slot Pin R to Pin 14 of 74LS42 (A14). Unfortunately still no luck. In fact Star Raiders no longer works. I tried reversing the address and RD lines just in case too. The computer is good because everything is fine when back on 16K. I suspect the RAM slot pin assignments on the Maplin board are quite different to all others? Later, I traced:- RAM slot Pin N to the RAM board's 74LS42 - Pin 13 (C input of decoder). RAM slot Pin R to the RAM board's 74LS42 - Pin 14 (B input of decoder). Not sure if this makes sense! Thanks guys.
  8. davemac
    Thank you again everyone. I made some progress today, but I still have issues! I dont know what RD4 and RD5 are referring to. I can't see these identifiers on the cct diagram - please help! I have connected mod wires as follows:- R to pin 14 of the 74LS42 (A14) T to Pin 13 of the 74LS42 (A13) M to Pin A of J108 (Cartridge slot) N to Pin 14 of J108 (Cartridge slot) Now when I power up the 400, I get a plain black screen (better than brown I guess!) Oddly though Star Raiders works fine! Donkey Kong does not. I'm going to borrow a BASIC cartridge tomorrow and try ?FRE(0), assuming it will boot at all! The image below is from the standard 16K to 48K mod instructions. Stargunner - I think this is what you thought was correct, but perhaps my card is different to the modded ones because I don't see any reference to RD4/5. Thanks, Dave.
  9. davemac
    Thank you all again for such useful information. I've not been able to get near the Atari this week due to graduation ceremonies where I work. I'll let you know how I get on eventually! Cheers, Dave
  10. davemac
    Thanks for the extra information. I'm guessing that if the mod wires were not present, the whole machine wouldn't boot at all? Perhaps it would still boot, but 'see' just 16K of RAM? Cheers, Dave
  11. davemac
    Thank you all for your replies. This is really interesting. I'll try to work out the correct order for the mod wires from the track layout and 400 motherboard cct diagram. Thanks again, Dave
  12. davemac
    Does anyone remember a 48k card that didn't need mod wires?
  13. davemac
    Hello everyone, I bought my Atari 400 in February 1983. I thought it had been thrown out many years ago, but I recently found it in my mother's cupboards! I tried powering it up, but it won't work. I tried a known-good 16K RAM card from my old Atari 800 and Star Raiders plays fine. I remember spending every cent on upgrading the RAM from 16K to 48K back in '83, which worked fine up until I last used it, which was probably around 1989/90. The odd thing is that the motherboard needed no mod wires to make it work. I've looked at many threads on here and on other sites and all upgrade kits seem to have needed the 4 mod wires from the RAM connector to the ROM cartridge connector. My board is a 'Mapsoft' one, so I'm wondering if anyone else has seen one, and perhaps they can advise me as to how to go about troubleshooting faults on it. I've socketed every IC, and have replaced all 74LSxxx ICs, followed by the RAM ICs themselves. I substituted the Mostek 4564-20 ones for 4164-15 chips, which I'm told will work. The originals were 200mS, but the new ones are 150mS. All chips replaced are known-good and I've tried more than one of each just in case. I even tried the 4-wire mod in case I was going mad! Any help would be greatly appreciated. I have an oscillocope and a multimeter! Many thanks, Dave.
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