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 7:27:27 AM UTC-4, Crustyomo wrote: > > Stan, > > Sounds very finicky. I don't have any experience with the 1701 or that > board but as general issues go with these systems here's what I've > encountered on my systems. Bad S-100 connections, pull out boards, clean > with a polymer eraser, cut parts of eraser to squeeze inside the S-100 > connectors and give them a scrub too, vertically only so you don't bend > their fingers. Just a little in/out action about a dozen times should do > it. The same goes for IC's on sockets. The sockets and IC pins get > tarnished. You might have to reseat the IC's, also about a dozen times. > I've even used the eraser on IC pins that were almost black. Yes, > capacitors are also likely suspects... but yours sounds to be a heat > related issue. My wild guess here is.. once a chip warms up a little, it > applies a little more pressure in the socket. Try a heat gun on certain > areas of the board but not too close, those things are hot. Hair dryers > are better. Then use cold spray to locate get the problem to re-occur. > Only do this after you've cleaned everything... this hot/cold treatment is > rough on the chips and should be used as a last resort. > > Good luck, > Josh Bensadon > > > ------------------------------ > Date: Wed, 25 Jun 2014 18:45:48 -0700 > From: [email protected] <javascript:> > To: [email protected] <javascript:> > Subject: [N8VEM-S100:4386] May I Interrupt this Designers Forum for Some > Help with Jade Double D FD Controller > > Hi folks, > > Please forgive me if this is a double post, but using my gmail account to > post, didn't appear to work, so I'm posting through googlegroups.com. > > 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 a bit > before daring to post, hoping to see another mere s100 user ask a question. > Hasn't happened. So here I go. > > 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 > accommodate 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). Floppy drive was also swapped out. > > 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] <javascript:>. > For more options, visit https://groups.google.com/d/optout. > -- 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.
