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May 25,2019
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NeoRAM Remix

The NeoRAM is a RAM extension for the Commodore 64/128 computers compatible with the GeoRAM modules from back in the days.
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Published: May 25,2019
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Topic
DIY Electronics
Cartridge GeoRAM NeoRAM Commodore C64
  • Comments(15)
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  • Thank you Hackupnet. This is a great project! The photos I have here are the 1Mb variant. I found the detailed instructions easy to comprehend as a beginner to soldering. The board is well laid out which makes for easy soldering of all components. The PCB has marking for all the components and orientations. I actually used some surface mount resistors instead of thru the hole components. These worked very well. The spacing of the solder pads was just right. Not sure if you intended this or not. I ended up opting for Cypress branded 512K x8 CMOS static RAM modules. The data sheet had them down at a slightly lower operating current and they were cheaper. https://www.aliexpress.com/premium/cy62148ell%25252d55sxi.html? d=y&origin=y&catId=0&initiative_id=SB_20200705200957&SearchText=cy62148ell-55sxi https://www.cypress.com/file/43851/download I found soldering the memory chips to the PCB easier that I expected considering their pin width. One will notice that the battery backup thru hole transistor is facing the other way round. I used a BC548, the pin out is reversed. I used some very old parts. I found some NOS 74174 chips dated 1977. They don't have a fabrication process identifier. I also used chips with various fabrication technologies. The finished NeoRAM PCB functioned well with these different ICs. I used as suggested low forward voltage drop schottky diodes on the battery backup circuit to help with prolonged battery life. I am not sure how long the battery will last in this NeoRAM PCB. The battery back up system has been tested and works OK with SID Tunes. In summary I found this a relatively inexpensive build. Fast and not too difficult to assemble

    Jul 06,20207 Comments
    hackup.net 2020-07-09 19:08:38Reply

    Thanks for the pictures and your comprehensive feedback! I'm glad you like the project.

    Mr Eddie Bannister 2020-07-15 17:07:00Reply

    :-)

    Jason Ginsburg 2021-10-12 20:16:27Reply

    I tried the Cypress SRAM chips linked above, no luck. I am not sure if they are the incorrect specification or if they were fakes (they did come from aliexpress). I tried again with the HM628512 mentioned in the hackup page and that corrected it.

    Mr Eddie Bannister 2021-10-13 11:19:35Reply

    Hi Jason, very interesting. I got a second batch of cypress chips from the above mentioned supplier. I too had bad trouble with them. I only got these 2 one sees in the posted pictures to work. I wasn't sure if my soldering skills were suspect or it was fake chips. I have created a forum discussion related to this...https://www.melon64.com/forum/viewtopic.php?f=12&t=14840 . Check out this link. Two days ago I received a delivery of HM628512 chips from Hackup.net's suggested AliExpress supplier. I have a new batch of boards coming soon so I can check if the Cypress chips are indeed fake. I will admit there is a great amount of fake chips in the market. By the way interestingly the 2 boards in the pictures worked first try. I've got a tub of suspect dead chips. Grrrrrr....

    Jason Ginsburg 2021-10-28 07:57:54Reply

    After a several week wait, I received today some HM628512BLFP-7 from Aliexpress (probably not the same seller though). I'm going to install some this weekend and will report back here.

    Jason Ginsburg 2021-10-30 19:42:00Reply

    Well, the HM628512BLFP-7 I received don't seem to work either. I'm just going to have to order from a real supplier.

    Mr Eddie Bannister 2021-10-31 10:11:50Reply

    Hi Jason, I'm sorry you got ripped off with a batch of dodgy chips. It happens more than we think. I recently received an order of 74LVC07AD SOP package style in sealed tape reel. I looked thru the clear plasticof the reel, all the chips have different markings. So evidently the seller's able to place random chips in factory packaging. How rude! I haven't gotten around to test them as yet. As for my delivery of HM628512 chips I haven't opened the antistatic package as yet. At least these came in an antistatic package! Keep us posted on how you get on. Join Melon64.com the people there are friendly. I'll keep you posted on how I get on with my HM628512 chips.

    Reply

  • Jul 06,20200 Comments
    Reply

  • 2Mb Variant.

    Jul 06,20200 Comments
    Reply

  • Jul 06,20200 Comments
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MARK HOGBEN
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Mr Eddie Bannister
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David Adams
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Terry A Paul
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