Hello all, Once again, it's spring^H^H^H^H^Hfall cleaning time, and I have a Mac IIfx CPU I no longer have space for. It's in excellent condition, has dual superfloppy drives, 32 MB RAM, a Radius video card, an Ethernet card, and an unidentified NuBus card from Apple (I think it was for the external 5-1/4" floppy drive, but I do not have the drive itself). I will also throw in another NuBus Ethernet card and a NuBus token ring card (FWIW). All I ask is that the buyer pay for the actual shipping charges, plus another $5 or so for the packing materials (I'm running low on this stuff). Or, if you're in the San Diego area, just come and pick it up! Regards, Stan Perkins Please note my new e-mail address: swperk(a)earthlink.net

Hi, Bill! If you go carefully, starting with noting the current dip-switch settings, I'd recommend you do the following. (1) set the dip-switches for the non-functional (suspect) board so they match the functional one. Install the suspect board with its new dipswitch settings and perform the same operations on it that you used with the seemingly functional one. If the behavior matches what you got with the seemingly functional board, you're home free. The hardware is probably working OK. You need to figure out your dip switch settings from their prior settings. It doesn't take a rocket scientist. Fear not! (2) attempt to isolate 4K blocks on the board's map, i.e. fill 0x4000 through 0x7FFF with zeroes, then read 0x4000-0x4FFF. Are the bytes all ZERO? If so repeat for 0x5000-0x5FFF, etc for each 4KB block. If one or more, including all, of these blocks fails to read all zeroes, fill 0x4000 through 0x7FFF with 0xFF. Read each block, making note of the results. If one of the 4K blocks fails to clear a single bit, that's cleared in another block, there's probably a failed IC or possibly a broken or intermittent enable or write command strobe in that RAM block. Make note and proceed. If one of the 4K blocks produces 0xFF but failed to produce zeroes, you've likely got a defective decoder or an intermittent or open write command, output enable command, or chip select to that block. If one bit is consistently wrong, it may be the memory device itself, but the stobe lines should be checked nevertheless. Memory IC"s are not much more likely to be at fault than logic devices or PCB taces. (3) now get out your meter and verify that all the memory IC's in a given bank have continuity on their address, select, write, and enable lines. If that seems correct, verify that the DQ or D and Q (if they have separate I/O) of all the memory IC's on a common data data bit have continuity as well. It's unlikely they'll be buffered separately. If these strobes are hooked up similarly to each device in a bank, and the data bits are hooked up similarly for each data bit in all four banks, then you should look for the TTL buffer to which they're connected. On boards of this age, these are likely to be 7436x's where x can be 5-8. it's most likely they'll all be the same, so I'd look for '367's using some combination of the groups of two and four bits that are enabled by each device enable. The S-100 has separate data in and data out busses, so there will be two sets of buffers. These buffers can be inverting or non-inverting, just so the same type is used on both busses. (4) now get out your oscilloscope and set up to examine coincidence of pWR* ( that signal was used pretty early on, though it had several names.) and the write strobe on your memory devices. If you see no activity on the write line when executing an infinite loop that writes to only one location in one of the banks of memory on the board. Find the right one by 'scoping the write lines on each row of 8 memory IC's until you have the one that goes LOW when the pWR* is low. Since you're in an infinite loop doing only one write to memory and a subsequent read of the same location, you should have no trouble finding the strobe if it's there. If you can't find it on the suspect board, you've probably found the problem, but now you should substitute the "working" board to ensure you've found the right signal. After ensuring you know where the select, output enable, and write command strobes are (which you can verify from a diagram of the device pinout) you should be able to verify that each of the strobes in question shows up on the working board as it should. Now go back to the suspect board and check each memory device to see which ones get the appropriate signals and which don't. Once you've established that the strobes appear where they should, look for the data to see that the correct data arrives and departs as it should. If that fails, you've probably found a defective memory IC. (do you see a pattern here?) If the strobes arrive at the correct time and the data arrives at the correct time during writes, (check setup and hold times, but those shouldn't be an issue if the board design works at all) and the correct data doesn't arrive at the CPU, then either the data-in bus buffers are defective, in which case the board won't work at all, or the select/enable logic is defective. If these parts are socketed, you can learn quite a bit by swapping them with parts from the board that works. Once you've got two boards that work all you have to do is find out how the switches work. As stated earlier, it doesn't take a rocket scientist to establish that. Dick ----- Original Message ----- From: Bill Sudbrink <bills(a)adrenaline.com> To: <classiccmp(a)classiccmp.org> Sent: Monday, September 18, 2000 9:12 AM Subject: Processor Technology 16KRA Docs?

Here's some info Bob Stek sent me last year on a similar problem... ---------------------- perhaps this will help: a15 a14 a13 a12 a15 a14 a13 a12 sw1-8 o o o o o o o o sw1-1 page 1 page 2 sw2-8 o o o o o o o o sw2-1 page 3 page 4 starting address a15 a14 a13 a12 x=open, off, down c=closed, on, up 0000 x x x x 1000 x x x c 2000 x x c x 3000 x x c c 4000 x c x x 5000 x c x c 6000 x c c x 7000 x c c c 8000 c x x x 9000 c x x c A000 c x c x B000 c x c c C000 c c x x D000 c c x c E000 c c c x F000 c c c c