General Stuff(tm)

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stephen_usher
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Re: General Stuff(tm)

Post by stephen_usher »

The only problem really with this old machine is that although the BIOS can handle the 8GB drive I'm trying to connect to it and I can set the parameters as a Type 47 MS-DOS can only access (and see) the first 514MB as the BIOS interface only allows up to 1024 cylinders and the drive is 16383/16/63

I mant to copy the stuff off the original drives as the C: drive is small and practically full and the D: sometimes causes the machine to hang at boot time.
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 »

Seeing that the solder side of the motherboard around the cache chips is mostly exposed with the machine in the case I had a quick prod of the cache chips with the oscilloscope.

The outputs from the upper two data lines on the QS888 cache tag RAM looked well dodgy. Lots of extremely short spikes rather than the nice square pulses on the other two. So, I've ordered another from the only place I can find them... eBay, from China. Estimated delivery is a month, if it's even the right sort of chip and it's not a repainted random.

I've also fond modern replacements for the cache SRAMs themselves and ordered 4 from Mouser. I hope they work. They're the same voltage, speed and pin-out.
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: Sun Jan 09, 2022 1:48 pm Seeing that the solder side of the motherboard around the cache chips is mostly exposed with the machine in the case I had a quick prod of the cache chips with the oscilloscope.

The outputs from the upper two data lines on the QS888 cache tag RAM looked well dodgy. Lots of extremely short spikes rather than the nice square pulses on the other two. So, I've ordered another from the only place I can find them... eBay, from China. Estimated delivery is a month, if it's even the right sort of chip and it's not a repainted random.

I've also fond modern replacements for the cache SRAMs themselves and ordered 4 from Mouser. I hope they work. They're the same voltage, speed and pin-out.
About to check the SRAM on my Aquarius, so I have sympathy for your situation!!
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 »

Ouch!

I managed to rig up the motherboard outside of the case so I could try different SRAM configurations.

Pulling half the chips just meant that the motherboard couldn't see any cache. Reseated all the chips and no difference. So I pulled the QS8888 tag SRAM, put Deoxit/Electrolube on the socket and reseated it and powered on.

Something smelt hot so quickly checked the SRAM chips... all luke war except the QS8888. Owwwww! I now have burnt fingers!

Pulling the chip and powering up the BIOS sees the cache but fails in the same way as it did before, which does suggest that the QS8888 might be the culpret.
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 »

Do you think that this set up is rickety enough?

IMG_2540.jpg
IMG_2540.jpg (78.75 KiB) Viewed 1434 times

I'm not sure that it's up (down?) to Exxos standards. :lol:
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: Sun Jan 09, 2022 4:13 pm Do you think that this set up is rickety enough?


IMG_2540.jpg


I'm not sure that it's up (down?) to Exxos standards. :lol:
Definitely could do with some more stuff strewn around if you want to match or beat @exxos :)
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 »

Hehe… maybe.

My next bit of diagnosis will be tricky. The symptom is that if the machine’s been powered off for a while when it’s powered on it doesn’t POST until the reset switch is pressed. There are no electrolytics on the motherboard, I/O card or graphics card and from the look at the rise time for the +5V and +12V they both come up pretty quickly.

Once reset the machine works normally. (Other than if the Seagate hard drive throws a wobbly, which it sometimes does after Crtl-Alt-Del.)
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: Sun Jan 09, 2022 10:53 pm Hehe… maybe.

My next bit of diagnosis will be tricky. The symptom is that if the machine’s been powered off for a while when it’s powered on it doesn’t POST until the reset switch is pressed. There are no electrolytics on the motherboard, I/O card or graphics card and from the look at the rise time for the +5V and +12V they both come up pretty quickly.

Once reset the machine works normally. (Other than if the Seagate hard drive throws a wobbly, which it sometimes does after Crtl-Alt-Del.)
Oh no, sounding a bit similar to my 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...
Tomswork
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Re: General Stuff(tm)

Post by Tomswork »

If it's a old pc with tantalum caps I would check for shorts on the power rails tantalum do short



Tom
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stephen_usher
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Re: General Stuff(tm)

Post by stephen_usher »

If there were a short the reset wouldn't fix it. I'm also measuring the voltages (GND + 5V & 12V) at the far side of the board and they're coming up quickly.

Also, from experience, when tantalums go short they often also go BANG and flame a bit.

P.S. I rescued the twin of this machine about 18 months ago and that had a similar issue, though I'd not recapped the PSU on that one before I gave it away.
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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