derkom's doings
Re: derkom's doings
Or at least don't turn them on until its the right way round
If it ain't broke, test it to Destruction.
Re: derkom's doings
Another side project... I am working on diagnosing a dead Stacy board (nope, not my project board, worry not!). I've got it booting DiagROM and I'm a little confused by the output I'm seeing...
At first glance, I thought "oh, some of the data lines are stuck low", but then I noticed when converting those hex strings to binary, it stops making sense...
It's not a simple case of some of the data lines being stuck low after all. Anyone have any thoughts on what could cause this behaviour? The CPU, MMU, GLUE, and RAM are all known good.
I had been considering hooking up the logic analyser to follow the individual bits through the LS244s and LS373s, to see if any of those are misbehaving, but now that I see this doesn't look like a case of individual bits not working, I'm wondering if there's some other diagnostic path I should be following.
At first glance, I thought "oh, some of the data lines are stuck low", but then I noticed when converting those hex strings to binary, it stops making sense...
Code: Select all
AAAAAAAA > 00A000A0
10101010101010101010101010101010
00000000101000000000000010100000
55555555 > 00500050
01010101010101010101010101010101
00000000010100000000000001010000
F0F0F0F0 > 00000000
11110000111100001111000011110000
00000000000000000000000000000000
0F0F0F0F > 00F000F0
00001111000011110000111100001111
00000000111100000000000011110000
I had been considering hooking up the logic analyser to follow the individual bits through the LS244s and LS373s, to see if any of those are misbehaving, but now that I see this doesn't look like a case of individual bits not working, I'm wondering if there's some other diagnostic path I should be following.
- stephen_usher
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Re: derkom's doings
It's almost as if one nibble is being swapped and the other goes nowhere.
Something to do with /UDS and /LDS during writes? After all the ROM is working, which means that the data lines must be OK, at least to the ROM. /UDS and /LDS aren't used for reading, which again means that if they're bad then it doesn't affect the ROM.
Something to do with /UDS and /LDS during writes? After all the ROM is working, which means that the data lines must be OK, at least to the ROM. /UDS and /LDS aren't used for reading, which again means that if they're bad then it doesn't affect the ROM.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
Re: derkom's doings
That's a good thought. I couldn't come up with any explanation for that bit-shifting/vanishing, but you may be onto something there. Gives me something to look into at least.stephen_usher wrote: ↑Sat Oct 31, 2020 2:30 pm It's almost as if one nibble is being swapped and the other goes nowhere.
Something to do with /UDS and /LDS during writes?
Edit: Can't really imagine anything is up with LDS/UDS. Those lines are present only on CPU, MMU, GLUE, cartridge port, and expansion connector, and everything seems fine. Both pulled up 2.2K (2.2K pullups on this board), 4.4K between them, and continuity on all the right pins of the three involved ICs.
- stephen_usher
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Re: derkom's doings
Actually, check the address lines going to memory, maybe the multiplexer. A4 going to memory being stuck may cause something like this thinking about it.
It's got to be beyond the ROMs otherwise the DiagROM couldn't boot. I'm trying to make sense of the schematics for the Stacy... Is the memory on a daughter board as it seems to be in the docs, with a header onto the RAM board. Bad connection on A4 or A5?
It's got to be beyond the ROMs otherwise the DiagROM couldn't boot. I'm trying to make sense of the schematics for the Stacy... Is the memory on a daughter board as it seems to be in the docs, with a header onto the RAM board. Bad connection on A4 or A5?
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
Re: derkom's doings
Yeah, the RAM, TOS, and keyboard controller are all on a daughterboard, which is known good, because it's my own and works fine in my Stacy.stephen_usher wrote: ↑Sun Nov 01, 2020 10:09 pm Actually, check the address lines going to memory, maybe the multiplexer. A4 going to memory being stuck may cause something like this thinking about it.
It's got to be beyond the ROMs otherwise the DiagROM couldn't boot. I'm trying to make sense of the schematics for the Stacy... Is the memory on a daughter board as it seems to be in the docs, with a header onto the RAM board. Bad connection on A4 or A5?
This evening I pulled a bunch of logic data off each D line, plus /RDAT, /WDAT, and LATCH both on the bus side of the buffers and on the RAM side, and while I haven't dug terribly deep into the output, it all looks like it's behaving correctly at first glance.
I also pulled almost the entire data bus, D0-D14 (needed the remaining channel on my logic analyser to pull /WDAT for a trigger), and it looks like the system isn't even putting the right data on the bus to begin with. I can see it set up the whole bus with one of the wrong results and then assert /WDAT, presumably storing the wrong data for later retrieval.
When looking at the schematics again tonight, I realised that the MFP is also connected to /LDS, so I socketed it and stuck in a known good one, no change.
It actually did occur to me in the shower today that something amiss on the address bus could be responsible for some bit shifting, so I added that to my list of things to look at. Quite a while ago I checked continuity on the whole bus, including the address bus, but I have not yet connected the logic probe to see what's going on there. Figured I would get to that after I finished pulling data off the data bus, so perhaps tomorrow.
Re: derkom's doings
Problem solved! I decided to start rechecking continuity (most interested in address bus, but looking at everything really), and everything between the CPU and MMU was good, so I went ahead and started checking the rest of the MMU connections, and discovered that there was no continuity between the 744 buffer output for CAS2H and the RAM. It was a shoddy factory solder job that eventually just broke. A reflow on that buffer chip (which oddly isn't on the schematics) has the board up and running.
- stephen_usher
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Re: derkom's doings
Yay!
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
Bell & Howell SR-II microfiche reader
A slightly different kind of retro has fallen into my lap. A friend of mine found this in the attic of an old commercial building he bought...
It's an old 1970s vintage Bell & Howell SR-II microfiche reader. It looks like it's probably mostly just dirty and in need of a new lightbulb, but we shall see!
It's an old 1970s vintage Bell & Howell SR-II microfiche reader. It looks like it's probably mostly just dirty and in need of a new lightbulb, but we shall see!
- rubber_jonnie
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Re: Bell & Howell SR-II microfiche reader
Crikey, I remember using these things somewhere. Where though, is another matter!!derkom wrote: ↑Sat Apr 16, 2022 12:38 pm A slightly different kind of retro has fallen into my lap. A friend of mine found this in the attic of an old commercial building he bought...
srii-001.jpeg
It's an old 1970s vintage Bell & Howell SR-II microfiche reader. It looks like it's probably mostly just dirty and in need of a new lightbulb, but we shall see!
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...