Are you saying there are only 3 bad cells? Could just be a bad trace. The data and address bus are muxed.
I would buzz out every pin on the suspect ram for zero ohms, to the 'end" of the bus. You may just find a weak signal, On Tuesday, July 5, 2016, Josh Malone <josh.mal...@gmail.com> wrote: > Thanks - just what I needed. So, I wrote a quick sequential RAM read in BASIC and I can't see any activity on the *CE line on M6. Writing a quick destructive RAM test, when writing to 32768 to 32790, the value I read back is just the offset from 32768 (i.e., 32768 = 1, 32769 = 2). I'm assuming that I'm actually reading the data line part of the shared address bus that's been latched in but never released. > > Soooo... does this sound like the SRAM or the decoder circuit? I'm leaning toward the SRAM, personally. All the other chips are working fine. I've also verified connection from M5 pin 12 to the *CE on M6. I'd have to disconnect the decoder from the SRAM to really see who's at fault, and if I'm getting out my iron to work on M5 (the decoder) I may well replace the darned thing since it's SMT. > > Guesses? > > Thanks again for everybody's help. > > -Josh > > On Tue, Jul 5, 2016 at 11:00 AM, Mike Stein <mhs.st...@gmail.com> wrote: >> >> pp. 7 & 8 of the Tech Ref: >> >> ftp://ftp.whtech.com/club100/doc/m102TechReference.pdf >> >> ----- Original Message ----- >> From: Josh Malone >> To: Model 100 Discussion >> Sent: Tuesday, July 05, 2016 6:30 AM >> Subject: Re: [M100] 32k M102 suddenly showing 24k >> >> Once I figure out the memory map that was exactly what I was going to do while probing the chip. >> >> On Jul 4, 2016 10:56 PM, "Doug Jackson" <d...@doughq.com> wrote: >>> >>> You could poke directly at the relevant memory ranges and see if a corresponding peek shows the data >>> >>> >>> On 5 July 2016 12:31:59 pm AEST, Josh Malone <josh.mal...@gmail.com> wrote: >>>> >>>> Okay. Thanks for the hints. Anybody know any good RAM diagnostic techniques for a 102? It's been a long time since I've used a scope in anger on anything but serial or audio. I'll dig into the datasheets tomorrow and see if I can gather any clues. A quick probing shows lots of address line activity on all four chips - mostly just testing that my scope can see these signals... It's been a while. >>>> >>>> Thanks again, >>>> -Josh >>> >>> -- >>> Sent from my Android device with K-9 Mail. Please excuse my brevity. >
