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  1. H

    Cromemco dazzler replica project

    Correct. R1 is 270 ohms on both RevC and RevD boards. There is a typo in post 340 - the reference to "R1 should be 30K" should have said "R11 should be 30K".
  2. H

    cdos, Cromix and ram

    I found an older (1980) version of the Cromix manual which only describes use of the 64KZ and no other RAM boards - which matches your experience.
  3. H

    cdos, Cromix and ram

    I just quoted what the Z80 Cromix Admin Manual said. Perhaps it was a later version published after the original 64KZ had been discontinued, and Cromemco was just targeting "new owners" with their manual.
  4. H

    cdos, Cromix and ram

    The 256MSU and 512MSU boards are very rare, and either of them needs to be paired with the MCU board that performs the actual error detection and correction. I am not aware of any third-party RAM boards that worked with Z80 Cromix. My guess is that if any existed, they would be as uncommon as...
  5. H

    cdos, Cromix and ram

    It's complicated. The 64KZ RAM board instruction manual provides a very detailed description of several scenarios under which a Cromemco system running CDOS can make use of multiple banks of RAM made up of 16KZ and 64KZ boards. The "typical user" would normally just run CDOS in a single 64K bank...
  6. H

    Cromemco dazzler replica project

    I expect you should be able to accomplish the same things a front panel does, with use of most ROM-based system monitors.
  7. H

    Cromemco dazzler replica project

    According to the schematic, test point "V" should be connected to pin 3 of IC14 - it will be inverted from pins 1 and 2 of IC14. You measure 3.5MHz at pins 1 and 2 of IC14, which is correct. IC7 pins 4 and 6 will also be 3.5MHz, just successively phase shifted from the signal at pins 1 and 2 of...
  8. H

    Cromemco dazzler replica project

    You may just have a poor signal feeding your scope when attached to test point "V". What do you see with the probe on either of pins 1 and 2 of IC14, with scope ground attached to pin 7 of IC14 ?
  9. H

    Cromemco dazzler replica project

    The Dazzler "1976 Rev C" manual has a very detailed diagnostic/troubleshooting section: https://archive.org/details/bitsavers_cromemcoCrctionManualRevC1976_8119234/page/n5/mode/2up
  10. H

    Am I seeing 192K RAM on this Z-120 correctly?

    Upgrading RAM on the original Z-120 main board involves more than just replacing the 64K RAM chips with 256K RAM chips. A kit containing the additional parts required (not including the RAM chips) was sold by a company called "FBE Research" called the ZMF-100" - it was sold back in the day to...
  11. H

    Cromemco dazzler replica project

    Those RevD scans are very good!
  12. H

    Cromemco dazzler replica project

    Yes - the Rev D manual copy I have, with the illegible schematic, is from the Cromemco repository.
  13. H

    Cromemco dazzler replica project

    Unfortunately the schematic in the scanned copy of the Rev D manual that I have is almost illegible - the small section I reproduced above shows just how bad it is.
  14. H

    Cromemco dazzler replica project

    This was mentioned earlier in this discussion - the Rev D board (vs the Rev C board that has been reproduced) included a couple of changes mentioned in Appendix A of the Games Manual for Dazzler board 2. This modification consists of a resistor/capacitor circuit added between IC50-12 and IC67-6...
  15. H

    Cromemco dazzler replica project

    For comparison, these are the boards I received from Hugo Holden. As he mentioned previously, the quality of these is better than the originals.
  16. H

    Cromemco dazzler replica project

    As Dave pointed out above "best practice" for 74 series devices is to pull up inputs that need to be at logic 1 via a resistor to Vcc. However, the designers of the Dazzler did not make any attempt to follow this practice. The Dazzler schematic shows over 2 dozen inputs to 74 series devices...
  17. H

    Cromemco dazzler replica project

    Good catch! I have one of Hugo's boards - and indeed, IC23 pin 10 is not tied to Vcc as it should. Fortunately the board still works since this connection (one of the flip-flop "preset" inputs) will float high if disconnected - however I should put a little jumper there to fix this issue "just...
  18. H

    Zenith Z-100 can read early 8" 86-DOS disks

    This is something I'd like to try on my Z100... would you be able to post your modified IO.SYS here?
  19. H

    Cromemco dazzler replica project

    These are advertised as "new old stock" - the manufacturing date is 1981 ? If so, you'll need to recap the board right after you finish building it :)
  20. H

    Cromemco dazzler replica project

    3.58MHz crystals in the HC-6/U can are still widely available as "new old stock" since they were very commonly used back in the pre-transistorized color TV era. If you do a web search on NTE358A (the crystal Hugo used) or NTE358B (the alternate) you can find many shops that still have stock...
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