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Thread: Commodore Dual Disk Drive 4040 repair attempt - ROM replacements

  1. #1

    Default Commodore Dual Disk Drive 4040 repair attempt - ROM replacements

    Hi Guys,

    I am T/S a Commodore DD4040 to be used with my CBM3032. Actually the self test gives an error code pointing to either the CPU 6504 or the RIOT 6530 but after some scopes measures they appear to be ok.
    I have checked the 3 ROMS and two of them are badly corrupted. I need to replace those with 2532 eproms but I think that an adapter is required to have them working with the disk drive as the 2532 are not pin to pin compatible with the original mask roms used into this drive. Also as far as I heard, the adapter needs a bit of glue logic and resistors also.
    Any chance for a link explaining how to build those adapters?
    Thanks
    Rick

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    Quote Originally Posted by repetto74 View Post
    I think that an adapter is required to have them working with the disk drive as the 2532 are not pin to pin compatible with the original mask roms used into this drive. Also as far as I heard, the adapter needs a bit of glue logic and resistors also.
    Rick,
    The problem is that on the 4040 there are two CPUs (6502 and 6504) sharing the bus, so that the Phase 2 Clock is used to allow the 6502 to use the bus when its clock is high only. The other CPU runs on an inverted Phase 2. You will have to modify the chip enable signal (at pin 20) to add in the Phase 2 clock. Also pin 21 of the EPROMs will have to be isolated and tied to +5V for the 2532 to work properly.

    If no-one finds a link to a mod, I will sketch a mod that should work and post.

  3. #3

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    Quote Originally Posted by dave_m View Post
    Rick,
    The problem is that on the 4040 there are two CPUs (6502 and 6504) sharing the bus, so that the Phase 2 Clock is used to allow the 6502 to use the bus when its clock is high only. The other CPU runs on an inverted Phase 2. You will have to modify the chip enable signal (at pin 20) to add in the Phase 2 clock. Also pin 21 of the EPROMs will have to be isolated and tied to +5V for the 2532 to work properly.

    If no-one finds a link to a mod, I will sketch a mod that should work and post.
    Hi dave_m

    Thanks for sharing your knowledge on this matter . Well I have made a deep search over the net and really I do not find any project for a proper replacement of faulty ROMS on the CBM DD 4040 disk drive unit. Sounds weird that nobody had to replace any of the roms when repairing those units.
    If you have a schematic to start something with it would be great thanks!
    Rick

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    A peer review of this circuit would be welcome.

    4040 Mod.jpg

  5. #5

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    Quote Originally Posted by dave_m View Post
    A peer review of this circuit would be welcome.

    4040 Mod.jpg
    Hi Dave,
    your mod looks ok to me. However I've found more effective to make a little daughterboard adapter to replace these kind of ROMs, so I don't need to modify the hardware.
    Unfortunately, my adapter is all SMD (including the EEPROM) and probably isn't easy to assemble for everyone.
    I do provide gerbers for free and complete units too, but I need to cover expenses for them

    Best regards
    Frank IZ8DWF

  6. #6

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    Finally I have received the gerbers kindly sent by Frank IZ8DWF . I have never tried SMD soldering but this is a good opportunity to start with it. Waiting for the boards and components to arrive from Cina then I will try to mount the replacement boards.

  7. #7
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    Quote Originally Posted by iz8dwf View Post
    Hi Dave,
    your mod looks ok to me. However I've found more effective to make a little daughterboard adapter to replace these kind of ROMs, so I don't need to modify the hardware.
    Unfortunately, my adapter is all SMD (including the EEPROM) and probably isn't easy to assemble for everyone.
    I do provide gerbers for free and complete units too, but I need to cover expenses for them

    Best regards
    Frank IZ8DWF
    Frank,
    I assume the board assembly includes the programmed EEPROMs? This would be a good solution.
    -Dave

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    http://go4retro.com/products/23xx-adapter

    Been around for years. We've used them many times in 4040s. I think 4040 is OK, but some of the drives have 23XX units with active high selects.

    Jim

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    Quote Originally Posted by brain View Post
    http://go4retro.com/products/23xx-adapter

    Been around for years. We've used them many times in 4040s. I think 4040 is OK, but some of the drives have 23XX units with active high selects.

    Jim
    Yes, in the 4040, the 2332 ROM has pin 21 with high chip enable and pin 20 is low chip enable, and pin 18 is address A11. What would be the jumper configuration in your adapter? If a 28 pin package like a 2764 is required for your adapter, does it fit in the 24 pin footprint or what is the required clearance around the 24 pin socket?

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    From the link I shared previously, it's in the section called"Support":"Configuration".

    But, my point is that some ICs have a specific pin as an active HI, and then they have the same numbered IC next to it with that same pin active low. I think the 2364s in the 8050 have that. Commodore could do that because they owned the fab and could order the CE lines to be active high or low.

    Jim

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