Hello Stan, I have an *IMSAI *as well and every time I bring it out of hibernation I have to disassemble the front panel for some problem or another. This last issue was related to depositing to memory and the MWRITE signal. I ended up using a logic analyzer to actually see the timing difference between certain signals, which will be difficult with a single logic probe.
What I have always found was that there was corrosion on many of the IC pins, so I simply replaced every single one of them, cleaned all the sockets, and have had no further trouble. Now, in your system, there may be a similar situation with the *proper signal, but at the wrong time*. This can be caused by noise, old components or problems like what I found with IC pins and sockets. Can you try to bring up the system by doing a jump on start and not even having the front panel in the mix? My original system has (had) a Northstar disk controller and 5 1/4" drive and worked great - just used diskettes that were hard to find. I just completed my first "new board" which was the S100 IDE that allows the system to run from a compact flash drive. What I found on this site were a lot of individuals that are very generous with their time and willingness to help, so I hope there will be some suggestions to get your problem resolved. good luck with the detective work! Regards, Thomas On Thursday, June 26, 2014 6:11:11 AM UTC-4, Stan Katz wrote: > > Hi folks, > > I joined this group hoping to ask some hobbyist level questions. It's been > evident in watching the postings that this is a very close knit group of > Designers who enjoy the more esoteric aspects of > building/modifying/programming s100 hardware. Thus, I've waited months > before daring to post, hoping to see another mere s100 user ask a question. > Hasn't happened. So here I am. > > I've played around with an Imsai which I've had since "the dawn of time" > e.g. 1977. I installed a Jade Double D FD Controller around the early '80s. > I, of course, modified the 2708 boot bios on my CCS Z80 board to accomodate > the new FDC. This arrangement has been stable for over 20 years. Recently, > the FDC has become sensitive to turn on sequencing. The WDC 1701 comes up, > most of the time in a state where it doesn't recognize a disk has been > loaded. I have to cycle the power switch numerous times until the FDC will > work. Once the FDC works, it never fails until the next power down. I have > a logic probe, and have checked that the reset gets to all the chips on the > FDC that need it. Cycling the RESET toggle switch, after power up, doesn't > clear the "lock up". Figuring this might be noise due to old power supply > electrolytics, I used an ESR meter to check the "big guys" on 8 and 16 volt > buses. They read essentially zero. One can't discount the fact that such > large caps might read zero even if they have lost a critical amount of > capacitance. Anyone's thoughts about that? There are 4 tantalum caps around > the regulator on the FDC. All but one, read almost zero, the one reads 3 > ohms. I'm thinking of replacing it, but I have no hope that the solution > could be that simple. I've rebuilt all the boot sector software on the > floppies that brings up the the Jade DD FDC. No change. I have also checked > the 2708 boot prom image, and it's good. I burned a new image onto another > 2708, but the power up sequencing problem remains. And, oh yes, I've > swapped out the WD 1701 with the only other one in existence ( to my > knowledge). > > If this query is too much of an "interrupt" to the current design > discussions, please point me to a more appropriate forum. > > Thanks, > Stan > -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
