On 7/8/2019 9:29 AM, Gerrit Heitsch wrote: > On 7/7/19 9:43 PM, Jim Brain wrote: >> Memory in a 250466 PCB went flaky, so I tried my hand at repair. The >> PCB is the 3 ROM version, but with 4164 DRAMs. After desoldering the >> DRAMs, socketing, and installing some new DRAMs (all working now), I >> decided to see if I could switch the unit over to SRAM. It appears I >> and some other folks had similar ideas, as I see another project on >> Facebook to convert as well. I went a different direction and >> leveraged a small CPLD to do the conversion. > > That's a bit Overkill, you need just 2 TTLs to make it work. A > 74HCT573 and a 74LS32 or 74LS04 (*) will do the trick. Of course, but if I was just wanting to replace the DRAM with SRAM, Pasi already built a nice board to do exactly that :-) I wanted some programmable logic in there so I can play with things, as you might now see in the list postings. > Sure it does: > > http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/252278-1.gif > > > http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/252278-2.gif > Yeah, I missed a word there. I meant a _legible_ one. The service manual has a legible one, so I was able to verify. JimReceived on 2020-05-29 22:35:19
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