No, I'm guessing that the chip is holding its enable line high and never activating. I haven't read very far into the chip - I should finish the test. I'm just concerned that the enable line never goes low on this chip.
On Jul 5, 2016 10:10 PM, "Stephen Adolph" <[email protected]> wrote: > 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 <[email protected]> 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 <[email protected]> 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" <[email protected]> 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 <[email protected]> > 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. > >
