Altair update - upon further testing, I detected 4 bad 74123 chips on the D/C panel.. that's 4 out of 5. I didn't even trust the remaining 'good' part so i chucked it and replaced all the '123s with new stuff. Luckily, I +did+ have those on-hand. That front panel must have really suffered a calamity, and now I'm suspecting the glue logic on the CPU board as well. So I've set up the proto-tester again, and I'm running through all the chips on the CPU board - it's mostly 8T97 aka 74LS367 tri-state buffers. This thing +WILL+ work again.. =) On Thu, Aug 28, 2014 at 6:51 PM, drlegendre . <drlegendre at gmail.com> wrote:

First off, an update - All of the 74XX chips on the CPU board seem to test out just fine. I'm having a little trouble figuring out how to set up a really +comprehensive+ test for the 74123s and the 7473 / 7474 chips, as I'm not yet up to speed on stuff like "retriggerable monostables with clear" and "dual J-K flip-flops". I did come up with some basic sanity tests though, and that is what helped me cull out the bad 123s. At least I have plenty of spares of those types, so can always check by making subs. On Thu, Aug 28, 2014 at 7:26 PM, Chuck Guzis <cclist at sydex.com> wrote: Bear with me, it's a bit of a complicated answer. Yes, the front panel AC switch is still on the board, but it's not presently connected, nor do I know much about the 'early' history of the machine. By early history, I mean the period of time between the original build / first light and the eventual +removal+ of the D/C panel. When I received this machine, it was configured for a Z-80 system, but in a VERY non-working state.. what a cobbled mess!! Both the D/C panel and 8080 CPU board were in bags. The panel wiring harness had been _de-soldered_ from _some_ mainboard, but not from the _present_ mainboard - the present mainboard had the panel wiring _cut_ away to the machine, so it may be that the mainboard was cut-out from a second Altair machine and transplanted into mine. As received, the mainboard had 1/4" cut stubs of white wire protruding from all of the hookup holes. The D/C board had also experienced a small, localized fire at some point, around the extreme lower-left corner (as viewed from the front). As mentioned, I cleaned up and tested / replaced as needed any parts in that area. I'm assuming that whatever may have caused the fire could also be responsible for the rest of the bad chips on the D/C panel. Doesn't really matter, though - as it needs fixed in any case.

On Thu, Aug 28, 2014 at 10:55 PM, Chuck Guzis <cclist at sydex.com> wrote: I don't - I have a single RAM board, and it's a 64K DRAM unit - see previous posts in the thread. I'm in need of a small SRAM board, and just about to bite the bullet and buy one from eBay.

Time for an update. Here's where things stand (more like, where they lie) at the moment.. I've replaced all of the ICs identified as bad on the front panel with parts that test good - with a caveat or two. Some parts I'm just not sure how to set up a thorough test for, but they failed the +basic+ test I was able to set up, so I simply replaced those with parts that appear to be new and in excellent shape (and that do pass the basic test). So at this point, I have good reason to believe that both the front panel and the CPU board have good chips all around.. none of the current chips failed any of the tests I used to reject the parts they replaced. But the machine is still missing its marbles - bearing in mind that my only references are the Altair32 emulator and the documentation check-out procedure. On power-up, the panel LEDs match the pattern on the emulator, so that's good. But still, I can't get any sanity out of examine / deposit memory locations.. nada. The ex. next and dep. next will walk up the range, as indicated by the address LEDs, but I can't get any kind of data from the data LEDs. They're either all 'on' or all 'off', in most cases. I've tried this with the termination power both enabled & disabled, no difference. Unless anyone has a suggestion, I don't know what to do other than wait for the arrival of the new SRAM board, and see how it behaves when that's installed. Thing is, I have no real reason to doubt the existing DRAM board - other than the fact that I've been warned off of using DRAM with the original 8080A CPU board. And again, I can't say that the DRAM board is any more alive than the socket it's stuck in.. Any ideas? SRAM should be here on Tues or Weds. On Fri, Aug 29, 2014 at 9:51 AM, drlegendre . <drlegendre at gmail.com> wrote: