[Coco] Bad memory reported by Disto Coco III RAM Test by Tony Distefano

Michael R. Furman n6il at ocs.net
Wed Nov 16 11:36:39 EST 2016

Does anyone have a manual for the Disto Coco III RAM Test by Tony Distefano?


 I ran it on one of my Coco 3’s and it is returning an error, says that block 60 is bad, which I interpret to be 0x78000 to 0x79FFF

A second observation is that when loading certain programs in to BASIC from the CocoSDC those programs get corrupted at the same place every time. 

I was looking at the schematics to try to figure this out and I am a bit confused.  What I see on the schematic is each of the 256k x 1 chips on the 512 ram expansion board is attached to one data line and there are two sets of chips selected by WE0 or WE1.  The part I am confused about is what it means that a particular range of memory is bad.  If one data bit is bad across the entire 256k range I understand that one, that’s a bad chip. But it only seems to be bad in a particular 8k range of addresses, so maybe this is some issue with RAS or CAS or a flakey address line to only the WE1 set of chips?  

What would happen if C65 or C66 still in place?  Why do they have those RC filters on RAS and CAS anyway?

 Michael R. Furman
Email: n6il at ocs.net
Phone: +1 (408) 480-5865

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