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  1. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    I think you can get the extra address lines by ORing (RAS2 or RAS4) for one, (RAS3 or RAS4) for the other. But I'm not sure if there is a timing issue...
  2. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    To use 1 meg SIMMs you'd have to OR the three RAS signals into one RAS signal and do some logic to translate those RAS signals into the extra address lines you'd need, if I'm thinking right. Since write enable is tied together for all three banks at the motherboard, no need to do logic there.
  3. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    I've re-installed the memory card, 2176k is working fine after running the setup program. No need to change the jumper. I have the Compaq EGA card in this as well, along with a 1GB Sandisk CF card acting as a type 42 528MB IDE hard drive in an adapter (card slot type so I can change the...
  4. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    The stand offs have two spring tabs that hold them tight to the motherboard on the side with the memory card. With that spring taken into account, the stand off is about 2cm from the shoulder that holds the memory card above the motherboard. Edit: Added picture, this one has one broken of...
  5. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Can't measure with the board attached unless I remove the mainboard from my system, which I'm not going to do. From the surface of the board to the shoulder of the connector is... 1cm (at the C69 end). From the shoulder to the top lip of the connector is... 1cm. So, 2 cm overall height. The...
  6. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    I think Jameco in the US has new NEC D41256-08 (80ns) in stock. https://www.jameco.com/z/D41256-08-NEC-Corporation-IC-41256A-08-DRAM-256K-Bit-256Kx1-80ns_2287695.html
  7. H

    What was the excitement of your first PC?

    I majored in Computer Science in college, so I needed a PC for my classes. I was pretty broke at the time (summer of 1991) so I bought a 286/12mhz bare bones mini-tower with 5.25 high density floppy drive, Oak OTI-028 256k video with both digital and analog outputs (handy because I only had a...
  8. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Stock you can get to just over 4 meg with this 1536k card and a 2048k card in a 16 bit ISA slot. That's probably enough for a 286. I did notice that the setup program has an option for a 638 meg hard drive for Xenix, so that was definitely a Compaq supported option. I wonder if that was an...
  9. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    For the SIMM version, are you going to do 2x1MB parity 30 pin SIMMs and waste 1/4 of the RAM, or use 6x256k parity SIMMs? Edit: Thinking this over, to work with the three RAS signals without additional logic, you'd need to do the 6x256k SIMM design. Of course, turning those signals into the...
  10. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    The latest schematic looks good to me, maybe move the R6/C73 labels to the other side so they don't overlap R7/C74.
  11. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Ah, pin A4 is write enable for both bank 3 and bank 4, confirmed with the multimeter, just as silvervest had shown. Bank 2 WE is separate.
  12. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    R8 connects to pin 4 of U4 in bank 3, which makes sense as that's the RAS signal for bank 3.
  13. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Z1 pin 1 is VCC. Z1 pin 2 is U1 pin 13 (top side trace) Z1 pin 3 is U1 pin 12 (bottom side trace) Z1 pin 4 is U1 pin 5 (top side trace, goes between pins on U1 underneath the socket) Z1 pin 5 is U1 pin 11 (bottom side trace) Z1 pin 6 is U1 pin 6 (top side trace, goes between pins on U1...
  14. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Z58 pins 8, 9 and 10 are NC. (under the sticker) Z2 and Z3 pin 2 are NC. Looks like you did get that U55 pin 11 connects to Z2 pin 10 and connects Z2 pin 10 to U52 pin 2.
  15. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Z1 is labelled as Z1, it's hard to see because the top of the Z is the silk screen around the resistor pack, and the bottom connects to the silk screen box around U1. A4 connects pin 3 of U46, using a trace that runs under the silkscreen box across the bottom of the connector. It goes over...
  16. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    For your enjoyment, an upside down front series of photos, including one I lit to see the connector more clearly.
  17. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Minor updates for your schematic: C70 connects to R5, other side of R5 connects to pin 3 of U1 (Bank 4) C73 connects to R6, other side of R6 connects to pin 3 of U7 (Bank 2) I mean, it's not wrong in that WE is connected together, but R6 does connect across the board at bank 2, not directly at...
  18. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    I used the top of my little Engel 63 quart chest freezer to try to keep the camera about the same distance from the card, sliding the camera along one of the seams in the top. Seems to have worked.
  19. H

    Compaq Portable II, Recreating the 512/1536 Kbyte System Memory Board (104176-001)

    Pin 1 of U57 connects to pin 19 of U57, which connects to R3 which is 150 ohms to ground. Pin 13 of U58 does connect to B11 on the connector, it does this with a trace on the top side that drops into a via, then around the back to another via just above B11.
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