Thanks, George, and Randy. Good suggestions. In this case the only scanbe sockets are the eight ram chips. I'll check them but I would bet the RAM test in the diagnostics is the first beep. All the rest of the sockets are already the Augat type. Looks like I'm going to start disassembling the firmware to see what that might reveal. George L. Rachor Jr. wrote:

On Sat, 3 Sep 2005 00:27:19 +0100 (BST) ard at p850ug1.demon.co.uk (Tony Duell) wrote: Somehow I had guessed for authenticity purposes, you would be campaigning for people to _preserve_ these sockets. Nightmare-grade unreliable sockets are part of the history of the particular machines they were installed in. I guess you don't view it as an issue. Were machine-pin sockets even _available_ when some of the early machines were produced? Note- I didn't make the above comments to start a flame war.

My policy on repair/restoration has not changed since the last time we had this 'discussion' on the list.... A classic computer should, if at all possible, be got working. The use of a computer system is to run programs. If it doesn't work, it's just a metal box with some chips in it. However, you should replace as little as possible to get it working. This means replacing simple componnts, not whole boards. It also means not replacing things _unnecessarily_. The electronic design of the machine should be unchanged. In particular, replacing the guts of a classic computer with a PC running an emulator is not 'restoration' (this does not mean emulators don't have a use in preserving classic computers and their software, it just means that an emulator is _NOT_ the classic computer). Now, as a hardware person, I would claim the electronic design goes way beyond the design of the CPU, It includes the peripherals, and the PSUs. BUT, I don't have any problem at all with designing plug-in interfaces for classics to modern peripherals (doing that does not in any way damage the rest of the machine). In the case of PSUs, I'd rather they were kept original. If you haev to replace a linear PSU with an SMPSU to save electricity, then IMHO the original linera PSU should be kept with the machine (and preferably left in place, with the SMPSU hung off the back of the rack!). I would also do small modifications to improver perfomance or reliabilty. I have no problem with filling up a half-stuffed memory board, for example. I certainly have no problem with replacing cheap IC sockets with turned-pin. If I desolder a programmed chip to dump the contents, I often (but not always...) put it back in a socket, and if I do that, I always use a turned-pin one. There you are. My $0.02's worth. Probably not. But then neither was 74F-series, and I've used those to replace 74S in classics. I'd rather use the right part, but if you can't get it.... In the case of a rare machine, you should keep a record of all the work you've done, of course. If the service manual is in a looseleaf binder, I put an extra page in the back with the modifications detailed. -tony

Joe R. wrote: Now Joe, Don't be so cynical! ;) You know that Intel provided some of the best documentation of anyone in those days. I just don't happen to have the right manual that describes that diagnostic. I believe it existed but was mainly for the repair techs. I have lots of good docs, as you well know, and as you do also, but it seems that we might both be lacking the particular one I need. I was able to get in touch with one of my old buddies who was an Intel repair tech. He said that at one time he had the source code for the firmware in that IOC board. Boy! I would like to have a copy of that, but he didn't keep it and is retired. Unlike me, he HAS a life and enjoys other things, so he got a kick out of my struggles with this IOC. BTW, I have managed to disassemble a good portion of the 1.3 version of the firmware (not the newest, but something that I started disassembling many years ago) and figured out some of the beep codes. Beep 1 and Beep 2 happen after checksumming the EPROMs. The pause next is a RAM test. It has 2108's, eight of them, so that is...a whopping 8k bytes I think! It takes a 2.4MHz 8080 a little time to cycle through them. The third beep signifies that the RAM test was successful. Next is still kind of fuzzy. It looks like it starts using a real stack, since the ram is good, and then initializes the CRT controller chip. It looks like it needs to see some kind of status returned from it to continue. There are at least three places that it can halt before the next beep, and the 8275 CRT controller is one of them. So that may be my problem. Now I'm looking for an 8275 chip. Can't find one just yet, but I just started looking. I might have to disect a working MDS to swap some chips. BTW, the one white MDS I got from you that didn't work...well, the IOC was totally dead on it. Based on this work on the disassembly I determined that the first beep can also fail to happen if the 8253 counter/timer chip isn't working. That is one of the signals that gates the beeper "on". I replaced that chip on the IOC from that machine and now it gives me three beeps, just like the one that started this whole journey. Interesting, at least to a nerd like me. Well, more to come, I hope. What a way to spend a long holiday weekend! At least it doesn't cost me any gasoline to do this!!! Take care, and I'll keep the list posted if there is anyone interested. Dave

Tony Duell wrote: Today in a failed attempt to repair the IOC board, I resurrected some ancient hardware. The IOC board is the back panel board on an Intel MDS Series II that handles most of the I/O of the system. It does a lot! It is based on a 2.4MHz 8080A cpu. Well, I broke out an Intel ICE-80 and hooked it up. This is the first In-circuit emulator that I know of, perhaps the first ever. It is quite primitive, but it can do a lot in the hands of a skilled operator. If I ever find such an operator, maybe I will be able to fix this damned IOC board!!! One of the problems I encountered with the emulator is because the RAM in the target system is dynamic. I think that when the emulation "breaks" from a breakpoint it seems that the RAM loses its contents. Perhaps the refresh circuitry relys on a clocking cpu. But it does look like I get inconsistent results reading the ROM on the IOC board. So I will now look at the buffer chips and maybe the address decoding. I tried to map the execution memory to the host MDS (that is the machine that is hosting the ICE-80), but since that slows execution and there are some software timing loops that didn't work very well. I am making progress, slowly. And putting two of these beasts together (one working one for the ICE-80 host, and the "target" system that needs to be fixed) isn't trivial. They weigh about 100 pounds each!!! It was a comical scene, though, with two MDS Series II systems side by side. I thought my table was going to colapse and the lights dimmed when I turned them on. ;) Stay tuned...I have some more disassembling to do. Dave

I'm looking for a keyswitch and number 0 (zero) keycap for an Apple IIe enhanced (A2S2064) keyboard: http://sturgeon.cac.psu.edu/~mloewen/Oldtech/Apple/AppleIIeE-3L.jpg Does anyone have any spare switches, keycaps, or a junked keyboard to spare? Thanks. Mike Loewen mloewen at cpumagic.scol.pa.us Old Technology http://ripsaw.cac.psu.edu/~mloewen/Oldtech/