DRAM 128K system has stopped working

[CheshireNoir]

Can I just start with a huge "Thank you!" to everyone for so much help.
Seriously, this is really heartening. keeps me going on this one.

Interesting that you are now having random problems with the TEST ROM memory test. Do the random failure happen on one particular bank or pair of banks or across all banks?

Seems to be across multiple banks. I've seen it on bank 0, 1 and 2 so far.

Quite probable that you have some contact issues either with the 2x 25 way headers between the Main and Core boards or even your IC Sockets, have good look at you EPROM socket. The original ones were not meant for multiple insertion removals and can be a bit of a problem. Are your RAM chips socketed?

I've cleaned the edge connectors with a very mild abrasive (ink eraser) and deoxit. I have reflowed all the pins on the core board edge connector. The socket for the ROM is a turned pin socket so should be good for a LOT of reinsertions.  The RAM is not socketed but I can socket it if need be.

The fact that BASIC fired up OK is a good sign, as this takes out a number of variables, bank switching and FDC being two main ones.

I'll take the progress where I can get it :-)

When you are saying that the neither the BN5443 nor the BN55 are booting up, earlier you described it as "doesn't even get a video sync" is this still the case or can you get into the Monitor with the BN5443 by powering up with the M key held down? If it is trying to boot the floppy through the FDC, you should get a block cursor at the top left of the screen until the floppy starts to boot, however depending on your setup may end up being off the top of the screen if your monitor is over scanning.

OK I did some extensive testing. When it doesn't work, I literally get "No Signal" come up on screen.
I have tried with both the BN5443 and the BN55 ROM. Both on startup give "No Signal" regardless of whether the M key is held down or not, and regardless of whether the Floppy Drive Controller Chip is in. Permutations FTW! No black cursor. I'd recognise that from when it was working. Pressing the reset key a bunch of times (in all permutations) usually gets a screen full of squares and symbols (Usually capital I characters) . Pressing the reset key a bunch of times with M held down usually gets a black screen. No cursor. This has changed along the way (M used to get me a Monitor screen but no keyboard. Whatever got the RAM test starting seems to have stopped the monitor starting). Most of the time pressing the reset key does nothing. Note this is only with the BN54 and 55 ROM. It works fine for Memory test. I haven't checked with BASICA+B

Depending on if you can get into the monitor or not will tell us if it is a floppy disk booting issue or a more sinister hardware problem with the Coreboard.
I don't have a BN55 EPROM to see if we can do the same there, but I would expect so.
The best I can tell is the BN5443 is meant for the 5.25" ds40 drives and the BN55 was for the 3.5" ss80 drives. It is possible that the routines for the ds40 access may have been replaced by those for the ss80, but I'm only guessing on this.

Hmm. I can't get into monitor at all any more, which points to something more sinister. I can run my TL866II+ over all the logic chips that are socketed, and now my desoldering station has a new gun, desoldering is a heck of a lot easier. I am happy to desolder chips as needed if you want to give me a short list.

I assume you are using a GOTEK for Floppy Emulation?

Yes, but as it isn't getting to the cursor screen, I haven't been plugging it in.

Ernest

Thanks again for all the help!

Hope these symptoms mean something to someone. I also have some photos of the screen if anyone thinks they'll help? Scope is on the bench, ready to go.

Cheers!

Chesh