General Stuff(tm)

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stephen_usher
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Re: General Stuff(tm)

Post by stephen_usher »

Well, other than waiting on the QS8888-20P chip from China I think the 486 is as good as it's going to get.

Last night I attached a newer (2000) IDE drive as master, copied off the data and reformatted the "D:" drive to get rid of the bad blocks and then copied the data back. This also allowed be to set the best "translated" CHS parameters in the BIOS and hence get the largest size (201MB).

The machine still doesn't always start first time when switched on but a quick reset afterwards always works, which is good enough. The PSU is outputting a constant 5.04V on the +5V line and 12.07V (+-0.01V) on the +12V rail, except when the drives are spinning up, when it drops to 11.95V.
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.
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rubber_jonnie
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Re: General Stuff(tm)

Post by rubber_jonnie »

stephen_usher wrote: Thu Jan 13, 2022 9:45 am
The machine still doesn't always start first time when switched on but a quick reset afterwards always works, which is good enough. The PSU is outputting a constant 5.04V on the +5V line and 12.07V (+-0.01V) on the +12V rail, except when the drives are spinning up, when it drops to 11.95V.
Sounds very like the problem I had with the Mac Classic.
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...
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stephen_usher
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Re: General Stuff(tm)

Post by stephen_usher »

Well, except that I can see that the power rails are coming up fine, though I've not tested the -12V. This feels like a motherboard issue now.

I thought that it might have been a PSU issue as every now and again the fan seems to slow and then after a few seconds speed up again, but the +12V is as steady as a rock (+- 0.01V).
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.
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rubber_jonnie
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Re: General Stuff(tm)

Post by rubber_jonnie »

stephen_usher wrote: Thu Jan 13, 2022 10:39 am Well, except that I can see that the power rails are coming up fine, though I've not tested the -12V. This feels like a motherboard issue now.

I thought that it might have been a PSU issue as every now and again the fan seems to slow and then after a few seconds speed up again, but the +12V is as steady as a rock (+- 0.01V).
Is there any current draw when it starts but doesn't boot?
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...
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stephen_usher
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Re: General Stuff(tm)

Post by stephen_usher »

From what I can see the power dips caused by load (which is all I can measure) are the same. I'm guessing that it's something in the reset circuit which is going out of spec., or the original design was close to the edge anyway and component age drift has just pushed it beyond the limit.
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.
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stephen_usher
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Re: General Stuff(tm)

Post by stephen_usher »

I found another QS8888 chip for sale on eBay yesterday which was from within the UK and delivery by the end of the week, so I ordered one.

Today I get an e-mail cancelling the order and saying, "Sorry, I can't locate the item." :-/

Why the heck would you create the sale if you don't actually have the stuff to hand? It just wastes everyone's time.

The chip from China still isn't due for about another month. (This assumes that (a) it's actually the correct chip and just not a random one with the correct number of pins which has been relabelled, and (b) actually works.)
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.
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rubber_jonnie
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Re: General Stuff(tm)

Post by rubber_jonnie »

stephen_usher wrote: Mon Jan 17, 2022 1:58 pm I found another QS8888 chip for sale on eBay yesterday which was from within the UK and delivery by the end of the week, so I ordered one.

Today I get an e-mail cancelling the order and saying, "Sorry, I can't locate the item." :-/

Why the heck would you create the sale if you don't actually have the stuff to hand? It just wastes everyone's time.

The chip from China still isn't due for about another month. (This assumes that (a) it's actually the correct chip and just not a random one with the correct number of pins which has been relabelled, and (b) actually works.)
This sort of thing drives me mad!! I'm sure they do it just to get you in front of their 'other items' in the hope you'll want something they do actually have!!
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...
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stephen_usher
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Re: General Stuff(tm)

Post by stephen_usher »

Hmm... I think this might be why there's a smell of burning electronics when I plug the second PSU into our core switch unit...

IMG_2544.jpg
IMG_2544.jpg (128.85 KiB) Viewed 1212 times
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.
User avatar
rubber_jonnie
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Posts: 10465
Joined: Thu Aug 17, 2017 7:40 pm
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Re: General Stuff(tm)

Post by rubber_jonnie »

stephen_usher wrote: Mon Jan 17, 2022 2:58 pm Hmm... I think this might be why there's a smell of burning electronics when I plug the second PSU into our core switch unit...
IMG_2544.jpg
Ooooh, scorchio!!
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...
User avatar
stephen_usher
Posts: 5578
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
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Re: General Stuff(tm)

Post by stephen_usher »

This evening I've been thinking again about how to implement the Apricot hard disk emulation, using a Raspberry Pi to emulate the WD1010 controller an much of the logic.

The original interface mapped the WD1010 registers to the I/O port addresses 0x0e2 -> 0x0ee (even addresses, i.e. low byte only), then from 0x1e0 -> 0x1ee write-only 1 bit registers plus the address 0x1f0 as the location to read/write to the 8K data buffer (auto incrementing the internal address register per operation).

Thinking about this further, I'm going to have to use some SRAM to emulate the WD1010 registers and it complicates things a bit that two of the locations read and write different things, e.g. 0x0ee reads from the status register but writes to the command register. I can't just use the Pi for this as it would be too slow to respond.

Similarly, the 8K data buffer and counter wouldn't be feasible for the Pi to drive directly, so I'll definitely need a counter (12 bit?) and an 8Kx8 SRAM.

Now, fortuitously I've bought 4 32Kx8 SRAMs for the 486 repair so I could use one of those for both the registers and the buffer and possibly the latch values, but this will need quite a few GPIO pins (and bi-directional level convertors) on the Pi end. The Sparkfun one can do 4 bits for £3, but space may be an issue.

Hmmm....
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.
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