Korean Mobo

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Korean Mobo

Postby toolfrolic » Thu Jul 19, 2012 2:06 am

Hi all,
my first post here.

The Mobo is operating and launching W95.
The DS12B887 RTC has died.
I want to explore the possibility of replacing the RTC, upgrading to W98 and adding a USB port.
I am in the middle of testing current generation IDE drives to see what data is reclaimable.

Identification:
Korean,
SUK JUNG ELEC,
SJ Pentium FX,
Rev c.

BIOS:
Award V4.50PG, 1995,
Triton Bios 2.10,
Plug and Play extension V1.0A,
String:
112795-110395-2A59CSCI-SJCTRITON-00

CPU:
Pentium-S 120 Mhz.

Thanks in advance for any comments and advice received.

John.
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Postby Twisty » Thu Jul 19, 2012 2:50 am

Is the rtc one of the ones with an internal battery? If so then that is probably what has failed. i think it is possible to cut into the chip and solder on an external battery.
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Postby evasive » Thu Jul 19, 2012 3:43 am

We hate rut, but we fear change.
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System error, strike any user to continue...
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Postby Karlsweldt » Thu Jul 19, 2012 8:48 am

That "Dallas" RTC chip design was a bad idea in several ways. Most were placed in sockets, but some were soldered to the mobo! Bad news there. But yes, it is possible to 'renew' its function with an external battery. Using a Dremel moto-tool or similar, or a dental drill, carefully burr away the area above the noted leads that are moved into the upper case area. The old battery can be left in place, but cut the leads to it.. or the battery could pop. And be cautious about excessive removal of the cover.. there likely is a crystal can in there, too!
Here is another link for a "fix".. http://www.mcamafia.de/mcapage0/dsrework.htm
And this site has a data sheet for the newer versions.. but you must subscribe to the site for the file.. http://www.maxim-ic.com/datasheet/index.mvp/id/2680
That RTC chip design was half the BIOS package.. one chip with 'odd' registers, the other with 'even' registers. Thankfully, only one BIOS chip is needed today.. and strictly an external battery!!
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Postby toolfrolic » Sun Jun 16, 2013 7:22 pm

Thanks for the responses and the links to RTC battery problems.
I have finally got around to the RTC - it is a DS12B887.

Removed chip from MOBO socket, cut plastic away from pins 16/20, and measured 3.01 V with a digital multimeter.
I reasoned that a new battery will do nothing, so replaced chip in MOBO without alteration.

The symptoms are still the same:
- turn on and select CMOS setup,
set date/time,
power off,
power on and select CMOS setup,
date/time wrong.

- turn on and let W95 come up,
set date/time under W95,
power off,
power on and let W95 come up,
date/time wrong.

The general CMOS data is retained OK, only the date/time is volatile.
I figure it is something other than the battery.
The RTC appears to be complex with modes and methods to write-protect selected data.
Is it possible something is wrong in this area ?

John
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Postby Karlsweldt » Mon Jun 17, 2013 5:50 am

Sorry to hear you still have problems. But if the clock and date won't stay up to date, likely other features are also failing.. such as the ability to keep the CMOS settings retained. There is a resistor in the lead from the battery, to limit current. If you don't sever the battery lead properly, then adding a "new" battery may result in no improvement. The old battery will act as a shunt to draw voltage from the circuit.
The Dallas RTC chip has a few variants.. mainly to the motherboard design and BIOS needs.
You cannot accurately check a CMOS or BIOS battery unless there is no other power to the system. Ensure the PSU has no input power, and a few attempts at starting are done to ensure reserves are drained.
Another issue, also, is the "Y2K" problem. Some BIOS versions were not compatible to the years 20** and beyond.. defaulting to the years 19** even after a 'save' process. No fix for that, except to reset the date/time on every start up.
You can still find the test software for the "Millenium Bug" to see if your BIOS is compatible to the year 2000 transition.
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Postby toolfrolic » Mon Jun 17, 2013 5:01 pm

Karl,
thank you for taking the interest.
This computer was a disposal by my nephew who updated to the latest.
The machine resides in the workshop and is destined to get LinuxCNC installed as a learning/developmental tool for my CNC mill (separate PC).

The date is always the 27th day of a random month in 2019, so unlikely to be a Y2K problem.

Soldered two leads onto the RTC battery - measured 3.05 V.
Installed in PC with leads to the multimeter.

During boot-up battery never wavered from 3.05 V.
Tried Reset without powering down, Date/Time is lost.

Tried altering the Parallel Port address.
New address retained both for Reset and power down cycle.

It really appears to be some sort of RTC internal fault, or faulty communication from the BIOS chip to the RTC chip.

If I get LinuxCNC running, I will try to get a replacement RTC.
John.
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Postby Karlsweldt » Tue Jun 18, 2013 9:51 am

The CMOS is powered by the same battery that keeps the real time clock active. But the RTC needs a crystal to provide a time reference. If the crystal does not get power, then the time and date will be off. There was no intent to power the RTC and CMOS externally.. bad design! From that link I provided.. http://www.mcamafia.de/mcapage0/dsrework.htm .. you can enlarge the image to note the features of the Dallas chip. Those two pins that are "missing" from the chip are tucked up over the chip for connection to the battery and crystal. You have to use precision in cutting away the epoxy, or the power circuit could be damaged. Yes, I did have a few 'bad repair jobs' when they were commonly used. The Dremel tool is the best to use, as you will note the change in sound when contacting metal instead of the epoxy.. and can retract from cutting.
The "internal" battery makeup was usually two small cells, some had only one small cell. Life was about 3 years or so before the battery died. No way the battery can be recharged, not designed for that!
The original battery may have been a mercury type, which is very dangerous to work with. Some were alkaline, the latest used Li-Ion batteries. Unloaded except for the test meter, even a "dead" battery may show good voltage.
If you can find a good replacement chip, work on that one to sever the internal battery lead and hot-glue a standard 3 volt battery atop it. Even a CR2016 battery should provide several years of service life. There are listings on eBay for the Dallas RTC chip. Some are listed as "new".. but buyer beware.
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Postby toolfrolic » Wed Jun 19, 2013 3:57 pm

Karl,
Although the RTC internal battery measured 3.06 V, I had a new battery with leads that I would be unlikely use anywhere else, so I cut the RTC internal battery lead and added the supplementary battery.

The new battery measured 3.57 V.

Re-entered all the CMOS data and tried date/time setting, PC Reset, PC Power Off/On.
Along the way monitored Vcc at the RTC, a solid 5.45 V.

Symptoms still the same.
Will not retain Date/time but will retain other CMOS settings.
The RTC operates correctly because it correctly nominates the day of the week when Date is entered.

When PC is running, Date/time on W95 displays correctly, and increments correctly at midnight.

Thanks for all the input.
I will not pursue this any further until I prove the PC will adequately run LinuxCNC.
John.
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Postby Karlsweldt » Thu Jun 20, 2013 9:00 am

Did you try that Y2K test from the link I noted? You have to do it from a floppy boot disk in DOS mode. But it is accurate and revealing. Many BIOS versions were 100% compatible, others would accept the change but not automatically. And some others would not accept the change at all!
Some BIOS types dated prior to 1992 were compatible, but even newer than 1995, some programmers deemed the system would be obsolete within 4~5 years.. so why bother with the "new millennium" feature?
If the CMOS settings are retained as to how the system is configured yet the date and time will not lock in, then likely your last recourse is to manually set the date and time on every start up.
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