-----Original Message----- From: cctalk [mailto:[email protected]] On Behalf Of william degnan Sent: Tuesday, September 6, 2016 11:37 AM To: General Discussion: On-Topic and Off-Topic Posts <[email protected]> Subject: Re: SWTPC 6800 weirdness
On Tue, Sep 6, 2016 at 2:25 PM, Brad H <[email protected]> wrote: > My 6800 has been mostly working, but it seems to be occasionally > flaking out. I don't know why. Sometimes you go to power it up, and > there's no response on terminal side. The 'fix' is sometimes to > wiggle the memory/CPU boards and then for some reason it's fine(ish). > There are five cards installed right now - the MP-A, MP-S, a heavily > modified MP-M board (with rams piggybacked on all the original RAM > chips) and then two Digital Research 16k boards. The system was > modified for Flex 2.0 > > > > Today it flaked again and would not come back up, so I pulled the MP-M > board and the MP-A board and swapped slots. It came up, but memory at > $0100 was > missing. I tried powering up, swapping slots, etc.. same deal. Then I > left the machine for an hour, powered up again.. boom.. now $0100 is back. > I don't fully understand the addressing system but if that MP-M is > configured as $A000 would that cover $0100 as well? > > > > I've tried changing the jumpers on each of the DR 16k board to cover > $A000.. > but the machine will not boot. I will only work with either the MP-M > alone or those 16k cards with it configured to other spaces. In other > words, the machine does not accept any other card configured for $A000. > > > > I'm wondering if anyone has any suggestions on how I might nail this down. > I'm thinking some of the RAMs on that MP-M are flaky, but it would be > a > *nightmare* to try and diagnose it, with all the RAMs piggybacked, all > the little jumper wires, and everything soldered. I'd prefer to > bypass it and either use my other, less modified MP-M or just the DR > boards, which are socketed. If any of you have suggestions on how I > might take this MP-M out of the equation that would be awesome! > > > Brad > > >Brad, >You'll need to make electrical measurements, from the system checkout in >the manual. You very possibly will have marginal components that need to >be replaced, but it's best to try to locate which is bad rather that to >replace at random. >A000 is not the same place as 0100. In the 64K space, they're quite >distant. >Eliminate all but the one RAM board, setting it to 0000. Test that >thoroughly, then add the next at the next RAM space beyond the first card. >Continue until you have enough RAM for a minimal Flex boot. It should tell >you in the version of Flex you're using how much that is (24K?) It's hard to >do everything at ?>the same time, break it down into chunks.. >Bill Thanks Bill. I've tried working with just single RAM boards, but like I said, the only one that will work at all is this modified board. I have pics of it here: https://drive.google.com/folderview?id=0B4pq0-BHd2x6WVFiZHdyMHBlNW8&usp=sharing If I could understand better what it is set up to do, what address spaces its occupying, I might be able to understand why my 16K DRC boards don't work when I try to put them to $A000. I'd prefer to work with one of those boards first since the chips are socketed, and then I could test the chips individually and be sure one whole board is good. I note in one of my pics there, the cap on that modified MP-M looks a little tarnished on the outside...
