VOGONS


First post, by UltimateElectronic

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I have an Olivetti Pentium 75 machine that I acquired a while back, the computer isn't broken, I was able to get it to POST and boot, but it had a Dallas DS12887a RTC chip on there which had died, unfortunately it was soldered in, but I did manage to remove it and now I have the mainboard with a socket where the chip was, but I'm still waiting to receive the replacement that I've ordered. Decided to turn the computer on with just the socket and no chip, as I concluded that the RTC probably wasn't necessary to get a screen to appear. So, could my conclusion of the board not needing an RTC to get a screen have been wrong, could the board have needed an RTC chip present to POST?

TIA,
UltimateElectronic.

Mainboard/computer specs, in case they're needed for additional diagnostics:

Computer model: Olivetti TINSL/II or PCS P/75 n,
CPU: Intel Pentium 75, socket 5
BIOS: AMIBIOS: 10/10/1994, Resident Diagnostics Ver, 1.12, BIOS ID 51-3103-000981-00111111-101094-SIS550X-Z
Chipset: SiS 5501, SiS 5502, SiS 85c503
Graphics card (integrated) : Trident TGUI9680

Reply 2 of 23, by PTherapist

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The only motherboard I have with a Dallas chip is also a Socket 5 with similar SIS chipset to yours, which also came with a Pentium 75.

With a dead Dallas, it would POST but not boot anything.

When I removed the dead Dallas chip (which was luckily socketed) and turned it on, it wouldn't POST but did display a picture showing a reboot loop as the BIOS initialized. So I'd hazard a guess that yes indeed, your board absolutely requires the Dallas chip to function.

Reply 3 of 23, by Daniël Oosterhuis

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I don't think most Dallas-equipped boards would be able to POST without one installed. It does more than just keep time, as it has NVRAM to store BIOS configuration properties. The board will likely try to access these at POST, then fail the POST as it never is able to access it. It's also why a lot of boards don't like empty modules, the lack of any BIOS config data in the NVRAM causes some to just not POST at all, rather than just boot with defaults selected.

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Reply 4 of 23, by dionb

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Agreed. Whether a board with Dallas RTC will boot or not with an RTC with dead battery varies (usually they do, but enough well-known exceptions), but with no RTC module at all, they generally will not.

If you're worried about going to the cost and trouble of a new RTC if you're not sure that the board even works, the solution is a sockek. Solder in a socket. If the board works, fine - and replacing RTC again will be easy next time. If not, you lost nothing more than a socket costing EUR 1 or so.

Reply 5 of 23, by UltimateElectronic

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Doornkaat wrote on 2020-12-12, 09:40:

I can't say for your specific board but it's not uncommon for boards not to POST without the RTC module. Some won't even POST with a drained battery in the module.

That's encouraging, I was able to get the computer to POST with a drained battery in the module, but it'd forget all of the BIOS settings as soon as I exited and it needed to be running for an hour to remember the settings. The only difference is that the rest of the module is now missing. Thanks for your help!

Reply 6 of 23, by UltimateElectronic

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PTherapist wrote on 2020-12-12, 11:05:

The only motherboard I have with a Dallas chip is also a Socket 5 with similar SIS chipset to yours, which also came with a Pentium 75.

With a dead Dallas, it would POST but not boot anything.

When I removed the dead Dallas chip (which was luckily socketed) and turned it on, it wouldn't POST but did display a picture showing a reboot loop as the BIOS initialized. So I'd hazard a guess that yes indeed, your board absolutely requires the Dallas chip to function.

Yeah, that's what I'm beginning to think, I was able to get it to POST and sometimes even boot with the RTC battery flat but the module present, the problem was that after exiting the BIOS setup it'd forget everything, and it's slightly too old to have proper auto HDD detection, so it was often unable to boot. I guess I'll have to see what happens when I get the new RTC module. Wish that the Dallas RTC in my board was socketed, would have made things much easier.
Thanks for your help!

Reply 7 of 23, by UltimateElectronic

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Daniël Oosterhuis wrote on 2020-12-12, 11:23:

I don't think most Dallas-equipped boards would be able to POST without one installed. It does more than just keep time, as it has NVRAM to store BIOS configuration properties. The board will likely try to access these at POST, then fail the POST as it never is able to access it. It's also why a lot of boards don't like empty modules, the lack of any BIOS config data in the NVRAM causes some to just not POST at all, rather than just boot with defaults selected.

Hmm that's interesting, I have had a few boards with empty RTC sockets and I seem to recall not having much luck getting those to POST either... I ended up deeming all of those faulty. I'll definitely try the new RTC in those other boards as well to see if they come back to life as well. Thanks for your help!

Reply 8 of 23, by UltimateElectronic

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dionb wrote on 2020-12-12, 12:55:

Agreed. Whether a board with Dallas RTC will boot or not with an RTC with dead battery varies (usually they do, but enough well-known exceptions), but with no RTC module at all, they generally will not.

If you're worried about going to the cost and trouble of a new RTC if you're not sure that the board even works, the solution is a sockek. Solder in a socket. If the board works, fine - and replacing RTC again will be easy next time. If not, you lost nothing more than a socket costing EUR 1 or so.

Yeah, I imagine it'd vary from board to board. The board does work, just never got far with a flat RTC battery, although I sometimes could coax it into booting into the OS. I have installed a socket in place of the module which cost me 65 cents AUD. I also bought a (probably new old stock) Dallas RTC module for $2 AUD off eBay, so $2.65 AUD isn't a huge loss if it doesn't end up working. Thanks for your help!

Reply 9 of 23, by dionb

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UltimateElectronic wrote on 2020-12-12, 23:35:

[...]

Yeah, I imagine it'd vary from board to board. The board does work, just never got far with a flat RTC battery, although I sometimes could coax it into booting into the OS. I have installed a socket in place of the module which cost me 65 cents AUD. I also bought a (probably new old stock) Dallas RTC module for $2 AUD off eBay, so $2.65 AUD isn't a huge loss if it doesn't end up working. Thanks for your help!

The latter is almost certainly a waste of money. Even if it's NOS, the charge is almost certainly gone. You'll have to mod it - which you can also do with the dead one you desoldered. Dallas still exists (now called Maxim) and still makes new DS12887 RTC modules. If you don't want to mod an old module, that's the way to go, or you can get a replica, a little PCB with DS12885 and a battery.

Reply 10 of 23, by maxtherabbit

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I agree that a brand new module is the best option, however TRUE new old stock isn't terrible either. The clock doesn't run on brand new modules until it's booted for the first time so the shelf life is very long

Reply 11 of 23, by PTherapist

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Yeah I can echo the above, I got a replacement Dallas NOS from eBay a couple of years back. It's still working great and keeping the date & time, which is pretty amazing since I hardly ever use that PC.

Reply 12 of 23, by UltimateElectronic

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dionb wrote on 2020-12-13, 11:20:
UltimateElectronic wrote on 2020-12-12, 23:35:

[...]

Yeah, I imagine it'd vary from board to board. The board does work, just never got far with a flat RTC battery, although I sometimes could coax it into booting into the OS. I have installed a socket in place of the module which cost me 65 cents AUD. I also bought a (probably new old stock) Dallas RTC module for $2 AUD off eBay, so $2.65 AUD isn't a huge loss if it doesn't end up working. Thanks for your help!

The latter is almost certainly a waste of money. Even if it's NOS, the charge is almost certainly gone. You'll have to mod it - which you can also do with the dead one you desoldered. Dallas still exists (now called Maxim) and still makes new DS12887 RTC modules. If you don't want to mod an old module, that's the way to go, or you can get a replica, a little PCB with DS12885 and a battery.

Not actually entirely sure that it was NOS, I was just assuming that, given it was $2, but maybe it was a brand new one. I guess I'll have to try it in the board and see what happens. I'll probably ultimately end up getting one of the replicas that you mentioned.

Last edited by UltimateElectronic on 2020-12-14, 09:27. Edited 1 time in total.

Reply 13 of 23, by UltimateElectronic

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maxtherabbit wrote on 2020-12-13, 14:31:

I agree that a brand new module is the best option, however TRUE new old stock isn't terrible either. The clock doesn't run on brand new modules until it's booted for the first time so the shelf life is very long

Well, that'd be encouraging, not sure if the module is NOS or brand new. Ultimately, I plan to get some sort of maintainable replica for it.

Reply 14 of 23, by UltimateElectronic

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PTherapist wrote on 2020-12-13, 17:32:

Yeah I can echo the above, I got a replacement Dallas NOS from eBay a couple of years back. It's still working great and keeping the date & time, which is pretty amazing since I hardly ever use that PC.

Ah, even more encouraging. Not sure whether to hold my breath or not with the one that I have coming...

Reply 15 of 23, by dionb

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UltimateElectronic wrote on 2020-12-14, 09:25:

[...]

Not actually entirely sure that it was NOS, I was just assuming that, given it was $2, but maybe it was a brand new one. I guess I'll have to try it in the board and see what happens. I'll probably ultimately end up getting one of the replicas that you mentioned.

It could also be plain used, then 'refurbished' i.e. original markings sanded off and new markings printed on implying it being unused and of much newer date of manufacture. That's what commonly happens to chips from this sort of source for this sort of price. For most chips it's an inconvenience at worst (if your 74-series IC works, it hardly matters whether it was made in 1995 or 2019), but with things containing a battery it can be more problematic.

Reply 17 of 23, by UltimateElectronic

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dionb wrote on 2020-12-14, 10:04:
UltimateElectronic wrote on 2020-12-14, 09:25:

[...]

Not actually entirely sure that it was NOS, I was just assuming that, given it was $2, but maybe it was a brand new one. I guess I'll have to try it in the board and see what happens. I'll probably ultimately end up getting one of the replicas that you mentioned.

It could also be plain used, then 'refurbished' i.e. original markings sanded off and new markings printed on implying it being unused and of much newer date of manufacture. That's what commonly happens to chips from this sort of source for this sort of price. For most chips it's an inconvenience at worst (if your 74-series IC works, it hardly matters whether it was made in 1995 or 2019), but with things containing a battery it can be more problematic.

True that, not sure whether mine was 'refurbished' or not, but it arrived yesterday and it seems to be working, I'm still not holding my breath for it being a long-term fix, but it seems to be working for the moment, so I'll cross that bridge when I come to it. Thanks again for all of your help, I'll let you know how goes and how long it lasts!

Reply 18 of 23, by UltimateElectronic

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canthearu wrote on 2020-12-14, 10:42:

Get new RTC modules in Australia from RS Online.

https://au.rs-online.com/web/p/real-time-clocks/1898609

$20 delivered, not cheap, but they are new, and shouldn't take 3 months to turn up.

Cheers mate, I'll look into one of those after the one that I bought on eBay dies. Incidentally, that showed up yesterday and is now fitted in the computer.

Last edited by UltimateElectronic on 2020-12-18, 23:43. Edited 1 time in total.

Reply 19 of 23, by UltimateElectronic

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Great news, the replacement showed up in the mail yesterday, I placed it in the newly-fitted socket, and turned the computer on, and it was indeed the lack of an RTC chip that was the problem, the computer is POSTing once again, and the chip seems to hold a charge, although we'll see how long that lasts. 😉

Thanks again to all that provided advice and/or help, or replied to the post, a few have pointed me towards new chips or suggested maintainable replicas, I'll make sure that I explore both avenues when the current chip I have now dies.