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Re: General Stuff(tm)
Posted: 08 Jan 2022 23:37
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.
Re: General Stuff(tm)
Posted: 09 Jan 2022 13:48
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.
Re: General Stuff(tm)
Posted: 09 Jan 2022 14:24
by rubber_jonnie
stephen_usher wrote: 09 Jan 2022 13:48
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!!
Re: General Stuff(tm)
Posted: 09 Jan 2022 15:36
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.
Re: General Stuff(tm)
Posted: 09 Jan 2022 16:13
by stephen_usher
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:
Re: General Stuff(tm)
Posted: 09 Jan 2022 16:56
by rubber_jonnie
stephen_usher wrote: 09 Jan 2022 16:13
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 :)
Re: General Stuff(tm)
Posted: 09 Jan 2022 22:53
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.)
Re: General Stuff(tm)
Posted: 09 Jan 2022 23:30
by rubber_jonnie
stephen_usher wrote: 09 Jan 2022 22:53
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!!
Re: General Stuff(tm)
Posted: 09 Jan 2022 23:41
by Tomswork
If it's a old pc with tantalum caps I would check for shorts on the power rails tantalum do short
Tom
Re: General Stuff(tm)
Posted: 10 Jan 2022 08:20
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.