Real Time Clock. - UK Vintage Radio Repair and Restoration Discussion Forum

TALKINGWITHPYE · 20th Mar 2021, 12:05 pm

Hello from Dave, I have found that I have a 486 motherboard with a real time clock (Dallas) would the demise of this chip be the cause of the failure to read the A drive? The rest of the computer works fine but I would think the complete failure is not far away. Coments please.

Dave

Refugee · 20th Mar 2021, 12:55 pm

They have an internal battery.
I have seen photos of them where the owner has dug into the chip to access the internal connections and added a new battery strapped on the outside.

SiriusHardware · 20th Mar 2021, 1:02 pm

Hello Dave, I remember your previous threads about this and the measures you have taken so far (tried different drives, tried another identical multi i/o card).

You need to tell us the exact number on the Dallas device which is probably a battery backed RAM as well as a realtime clock.

If you think that device might be faulty, does the machine remember the time and date when it is fully powered down for a while and then powered back up again?

When you go into the BIOS settings, what sort of floppy drive does the BIOS show it is set for? From memory, repeatedly pressing 'DEL' while the machine is booting is probably the way to get into the BIOS.

I assume this is a particular floppy disc you need to be able to run. Putting that disc aside and taking an unused or unimportant spare disc, what happens when you try to format that spare disc? If you are able to format any other disc try copying a file from HDD onto that disc and copying it back off onto the HDD again.

ortek_service · 20th Mar 2021, 2:18 pm

The most common RTC module I've seen is the DS1287
and there's a video of how to resurrect one, here:
https://www.youtube.com/watch?v=NdlSfqto_0o

Although on a previous website I saw, they removed the original battery inside, from off the top.

If the internal flat battery is dragging down the supply to the CMOS RAM, then it may not be able to store BIOS settings properly, like FDD choice - even with power on. Although if left on for a while, the supply to this module may eventually be able to lift the supply to the RAM if leakage currents are able to charge the battery a bit.

There probably aren't too many new old stock ones around that are still new enough to have a very good battery. Although it is possible these are still being made - But were always quite expensive, compare to just IC and separate coin-cell.

20th Mar 2021, 2:26 pm

At work we have the same problem and we have NOS ones in stores, they do work, I wonder for how long though. The really annoying thing is that the real time clock isn't needed (just an embellishment) so the flash in the micro would have done the job.

If you can get your hands on the non battery chip you can bend up a couple of pins and attach a cell to them, that is what Dallas did with added epoxy.

SiriusHardware · 20th Mar 2021, 2:34 pm

There appears to be a current drop-in equivalent:-

https://uk.farnell.com/maxim-integra...5431?st=ds1287

Datasheet here

http://www.farnell.com/datasheets/1904690.pdf

seems to suggest it is pin / register / command compatible with the DS1287, although I would be inclined to scout around to see if the 1687 is indeed compatible without any changes to the host system. Note it is available in 5V (-5) and 3V (-3) versions, I imagine the 5V version would be the one needed.

However, with regard to solving this problem it might be prudent to go into the BIOS, change one non-critical thing, save the change, exit, power the machine down, wait, power up, go back into the BIOS, see if the change has been retained

If it has, then the Dallas IC does not need to be changed at the moment and is not the cause of the disc troubles.

TALKINGWITHPYE · 21st Mar 2021, 11:35 am

Thanks chaps, I have bought another 486 so the one with the real time clock is waiting for further investigation, as would you believe it, the barrel Varta batery is flat in the machine I bought. I am thinking of replacing the Varta with a button cell in a holder as I have seen the results of leaking Vartas, thankfully this one is clean. I was hoping to send my original machine to a friend in Skelmersdale who needs a machine with ISA slots so he can fit a Philips protocol converter card for programing FM11oo series radios.

ortek_service · 21st Mar 2021, 12:52 pm

Quote:

Originally Posted by TALKINGWITHPYE

Thanks chaps, I have bought another 486 so the one with the real time clock is waiting for further investigation, as would you believe it, the barrel Varta batery is flat in the machine I bought. I am thinking of replacing the Varta with a button cell in a holder as I have seen the results of leaking Vartas, thankfully this one is clean. I was hoping to send my original machine to a friend in Skelmersdale who needs a machine with ISA slots so he can fit a Philips protocol converter card for programing FM11oo series radios.

If that Varta battery is a NiCd one (blue), then they've generally been replaced by NiMH (green) ones, and seem less prone to leaking / may not have issues with rotting of tracks etc. (I've never seen AA type rechargeables leak, that ever cause damage to battery contacts, that Alkalines frequently do).
However some PC Motherboards also had primary Lithium cells, as well as maybe a rechargeable Lithum type coil cell, you can get.
I think the backup battery current on later PCB's was much less, as a lithium coin cell could last >10yrs, whereras you used to get plug-in 3xAA 4.5V Alkaline battery packs on earlier ones that only lasted a few years.

20th Mar 2021, 12:05 pm	#1
TALKINGWITHPYE Pentode Join Date: Oct 2018 Location: Carrickfergus, County Antrim, Northern Ireland, UK. Posts: 126	Real Time Clock. Hello from Dave, I have found that I have a 486 motherboard with a real time clock (Dallas) would the demise of this chip be the cause of the failure to read the A drive? The rest of the computer works fine but I would think the complete failure is not far away. Coments please. Dave

20th Mar 2021, 12:55 pm	#2
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: real time clock They have an internal battery. I have seen photos of them where the owner has dug into the chip to access the internal connections and added a new battery strapped on the outside.

20th Mar 2021, 1:02 pm	#3
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,560	Re: real time clock Hello Dave, I remember your previous threads about this and the measures you have taken so far (tried different drives, tried another identical multi i/o card). You need to tell us the exact number on the Dallas device which is probably a battery backed RAM as well as a realtime clock. If you think that device might be faulty, does the machine remember the time and date when it is fully powered down for a while and then powered back up again? When you go into the BIOS settings, what sort of floppy drive does the BIOS show it is set for? From memory, repeatedly pressing 'DEL' while the machine is booting is probably the way to get into the BIOS. I assume this is a particular floppy disc you need to be able to run. Putting that disc aside and taking an unused or unimportant spare disc, what happens when you try to format that spare disc? If you are able to format any other disc try copying a file from HDD onto that disc and copying it back off onto the HDD again.

20th Mar 2021, 2:18 pm	#4
ortek_service Octode Join Date: May 2018 Location: Northampton, Northamptonshire, UK. Posts: 1,440	Re: Real Time Clock. The most common RTC module I've seen is the DS1287 and there's a video of how to resurrect one, here: https://www.youtube.com/watch?v=NdlSfqto_0o Although on a previous website I saw, they removed the original battery inside, from off the top. If the internal flat battery is dragging down the supply to the CMOS RAM, then it may not be able to store BIOS settings properly, like FDD choice - even with power on. Although if left on for a while, the supply to this module may eventually be able to lift the supply to the RAM if leakage currents are able to charge the battery a bit. There probably aren't too many new old stock ones around that are still new enough to have a very good battery. Although it is possible these are still being made - But were always quite expensive, compare to just IC and separate coin-cell.

20th Mar 2021, 2:26 pm	#5
Guest Guest Posts: n/a	Re: Real Time Clock. At work we have the same problem and we have NOS ones in stores, they do work, I wonder for how long though. The really annoying thing is that the real time clock isn't needed (just an embellishment) so the flash in the micro would have done the job. If you can get your hands on the non battery chip you can bend up a couple of pins and attach a cell to them, that is what Dallas did with added epoxy.

20th Mar 2021, 2:34 pm	#6
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,560	Re: Real Time Clock. There appears to be a current drop-in equivalent:- https://uk.farnell.com/maxim-integra...5431?st=ds1287 Datasheet here http://www.farnell.com/datasheets/1904690.pdf seems to suggest it is pin / register / command compatible with the DS1287, although I would be inclined to scout around to see if the 1687 is indeed compatible without any changes to the host system. Note it is available in 5V (-5) and 3V (-3) versions, I imagine the 5V version would be the one needed. However, with regard to solving this problem it might be prudent to go into the BIOS, change one non-critical thing, save the change, exit, power the machine down, wait, power up, go back into the BIOS, see if the change has been retained If it has, then the Dallas IC does not need to be changed at the moment and is not the cause of the disc troubles. Last edited by SiriusHardware; 20th Mar 2021 at 2:53 pm.

21st Mar 2021, 11:35 am	#7
TALKINGWITHPYE Pentode Join Date: Oct 2018 Location: Carrickfergus, County Antrim, Northern Ireland, UK. Posts: 126	Re: Real Time Clock. Thanks chaps, I have bought another 486 so the one with the real time clock is waiting for further investigation, as would you believe it, the barrel Varta batery is flat in the machine I bought. I am thinking of replacing the Varta with a button cell in a holder as I have seen the results of leaking Vartas, thankfully this one is clean. I was hoping to send my original machine to a friend in Skelmersdale who needs a machine with ISA slots so he can fit a Philips protocol converter card for programing FM11oo series radios.