RE: [N8VEM-S100:4386] May I Interrupt this Designers Forum for Some Help with Jade Double D FD Controller

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: stan.k...@gmail.com
To: n8vem...@googlegroups.com
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

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