interesting, this is not the first time that I've seen or heard of an IC output failing on the memory circuit. Saw the same thing on a PC8201 from Terry in NZ a number of years ago. A failure that is unexplained other than straight silicon failure. no static, no copper track issue etc.
On Tue, May 9, 2017 at 6:52 AM, Josh Malone <[email protected]> wrote: > I guess I'll forward this without my picture. It's a shame this list won't > take attachments bigger than 64k. Does this mean that everyone who wants to > share this sort of thing goes over to Facebook? Or where? > ---------- Forwarded message ---------- > From: "Josh Malone" <[email protected]> > Date: May 8, 2017 10:19 PM > Subject: RAM issues continued > To: "Model 100 Discussion" <[email protected]> > Cc: > >> So, I've finally made a breakthrough in my 102 RAM issue. If you recall, >> my 32k machine cold - started on me one day and from then on it only showed >> 24k. I replaced the sram to no avail. After that pain in the @$$, i kinda >> have up for a while. >> >> I finally got my hands on a hot air station, and I was able to wing a pin >> on the M5 mux so i could scope it independently. Sure enough, no activity on >> the line. So the decoder circuit was never enabling the option RAM. I was so >> proud of my rework! >> >> So, my next step is to track down a replacement for the mux. I removed the >> chip without to much difficulty. It's a 40H139F. Hopefully not too hard to >> source in that package. >> >> Wish me luck! >> >> - Josh
