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Everything posted by ClausB

  1. Wonder if there's enough room in the FPGA for an ANTIC core.
  2. Yes, look at the list. The serial numbers are not serial. That's why we go by datecode.
  3. Missing 3-digit date code. Check rear underside, as in ApolloBoy's post above.
  4. Those are awesome! They are squashed though. The circles on the locomotive should be circles. You should fix the aspect ratio in your emulator and take new screen shots.
  5. Here is that letter from page 360 of BYTE, September, 1981:
  6. Well this is interesting! Page 51 has a letter asking about Atari RAM and RS-232 upgrades in summer of 1981. By then I was reading BYTE profusely and Ciarcia in particular. That is exactly the time when I did my first RAM upgrade on my 400 and built a modem kit. I added 8 4116s to my Axlon 32K, just as the letter suggests. And I connected the modem to the SIO port, just as the answer suggests. I wonder whether I got the inspiration from this page. Ciarcia clearly didn't research the Atari architecture before answering, as it already had the refresh logic built into the RAM boards and the ANTIC chip. His answer about RS-232 was spot on though, since POKEY could do all the serial work. All you need to add is voltage level conversion. Here's the RAM upgrade: Here's the modem project:
  7. Atari 400 and 800 power supply caps rarely fail and don't normally need replacement. Not sure what you mean there. GND on the header should be part of the ground plane.
  8. Huh? Relative to what? Where are you placing the black lead of the voltmeter? What were the readings before recapping? Was there a reason for recapping?
  9. Thanks for that! BYTE was the best IMO. In 1976 our high school computer club subscribed to BYTE and some others. I was a novice programmer and BYTE was over my head, a bit heavy on hardware, so I ignored it. Later in college, I frequented a computer store with a book and magazine rack. I had learned much more about software and hardware so I started buying and reading BYTE. It had a great overview of the budding industry. After the store closed, I subscribed. Later I went back to the high school and bought the back issues from the club. I finally completed my collection, buying the earliest issues, none too cheaply, from classified ads. I've kept those first ten years' issues as a chronicle of microcomputing history and nostalgia.
  10. Congrats on the repair! For your next challenge, fix that donor board.
  11. Yes, the 4108 is just a 4116 with bad bits in one half. So you can use 4116s for your missing chips. If you are a stickler for authenticity, I might have the 4108s you need. I can look this weekend. If you want to upgrade the board to 16K, see the side bar in my article: https://atariage.com/forums/topic/123207-expanding-the-400/?do=findComment&comment=1488304 If you want to upgrade the board to 48K for use in an 800, see my thread: https://atariage.com/forums/topic/298603-old-school-hack/?do=findComment&comment=4404603 I don't have a BOM but the original schematics in the thread above are from Atari and they call out part values.
  12. 27256 is the correct EPROM for the XEGS. It's 32K and it has OS, BASIC, and a game. 28256 is the EEPROM version.
  13. Try swapping in the 74LS42 or LS32 from the working board. They are the only chips with different signals between slots 1 and 2. Reseating all the chips might help.
  14. I built two ZX81 kits and met a lasting friend who had a ZX80. Thanks, Sir Clive!
  15. Thanks, that confirms it. If you want 256K, wire U20 pin 1 to ground and insert a 74LS153 into the socket at U20. BTW, this isn't an attempt to modify the 1066 into what it's not. Clearly the original designers had 256K in mind. They got most of the way there and then backed off for some reason. The date on the original schematic is May or June, 1984, months before I designed the 256K upgrade for the 800XL which appeared in BYTE a year later.
  16. It's hard to tell from the photos whether those are copper connections or just silk screen lines. Could someone post a close up photo of U20 and U21 on the bare board, maybe both sides?
  17. From the board photos it appears that U20 pin 1 goes to U21 pin 19. If so, that's fine and it doesn't need to go to ground. It also appears that U20 pins 1 and 16 are connected. That's bad. Pin 16 should connect to +5V, not to pin 1.
  18. I took the liberty of modding the schematic for 256K. In the process I found that U20 pin 1 must go to ground. It might help to remove R25 too.
  19. Right. As it stands you could have two 256K boards plus one 64K in 1064 mode for a total of 576K.
  20. Looks like the board is already designed to handle 256K. Just plug in some 41256 DRAMs instead of 4164s, and plug a 74LS153 into U20 and you're good. (This will also require the newer ANTIC.)
  21. My warning has nothing to do with bank switching, only with refreshing. The schematic says 4164 RAMs (7 bits refresh), and that's what the board needs. Daisy chaining, eh? Interesting.
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