250466 PCB curiousness

From: Jim Brain <brain_at_jbrain.com>
Date: Sun, 7 Jul 2019 14:43:30 -0500
Message-ID: <b799b1d3-f918-8cd2-d8c2-b0832e93774a_at_jbrain.com>
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.  After fighting last night with 
unsoldered pins, it is now working.

I decided to play around with the unit and map out the address pins.  
Interestingly, I find that MA6 and MA0 appear to be swapped on the PCB.  
I verified that MA6 indeed goes to MA0 on the 6567, though without a 
schematic, it's hard to trace MA6 (it goes through a '257, etc.).  
Anyone have a schematic? (Zimmers does not appear to have one) And, does 
anyone know if pin swapping was done on other versions?


-- 
Jim Brain
brain_at_jbrain.com
www.jbrain.com
Received on 2020-05-29 21:49:03

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