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.
