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27804re: [midatlanticretro] EconoRAM VIIA Issues

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  • B. Degnan
    Oct 23, 2012
      You may have bad jumper switches for the 8K bank, causing a conflict. See
      if you have similar problems with other RAM combos that include the same
      jumper used to set for 0000 (are they really off then they are set to off).

      It could be that the replacement RAM is not as fast as the original, but I
      assume you have ruled that out.

      My guess. I think I have one or two of these cards, they're usually


      -------- Original Message --------
      > From: "Kyle Owen" <kylevowen@...>
      > Sent: Tuesday, October 23, 2012 8:37 PM
      > To: midatlanticretro@yahoogroups.com
      > Subject: [midatlanticretro] EconoRAM VIIA Issues
      > I recently got a few MK4104 4k by 1 bit SRAM chips to replace a few bad
      > MM5257s on my CompuPro EconoRAM board. I also wanted to fill out the
      > RAM board, so I needed 10 total chips, 8 for the 4k bank, and 2 to
      > the bad 5257s. After putting it all back together, I noticed that my 4k
      > bank at $0000 is testing bad. The odd thing is, it is very intermittent
      > the same bytes that test bad one time may test good next. I wrote the
      > test utility as a part of the ROM monitor that I'm using. It writes $A6
      > $6A respectively, to test all bits for 1 and 0. All other RAM tests just
      > fine. The board itself is divided into 4 banks: two 4k banks and two 8k
      > banks. Each can be positioned anywhere in RAM so long as it starts at
      > Here's the weird thing. The same bank of RAM, when positioned at
      > but $0000, works just fine. The other 4k bank in position $0000 has the
      > same issues as the first 4k bank.
      > But things get weirder: either 8k bank at $0000 works just fine. So all
      > all, I'm not sure what the heck is going on. I can't really tell from
      > schematic what component would only fail when the card has either 4k
      > jumpered to $0000.
      > The manual for this RAM board can be found here:
      > Any ideas would be very much appreciated!
      > Thanks,
      > Kyle
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