the DS1287 / DS1387 RTC chip
|The Situation: You have either a PS/2 25-286, 30-286,
55 or 65 which comes up with a "165 configuration error" and fails to
keep the setup once been shut off again.
Well - these have the dreaded Dallas DS1287 "all in one" Real Time
Clock (RTC) chip with integrated Xtal and battery. Now the battery is
dead, configuration is lost after relatively short time again and you
get error-codes constantly. A really new, fresh and unused chip is hard
to get. Even its successor DS12887 is pretty hard to get and darn
At that point you wish you could add an external battery.
But you can't. There are no provisions for one.
The Action: Have a look at the graphics below..
Click to enlarge
Drawing © 2006 by Peter H. Wendt /
Basically the DS1287 is a DS1285 chip, where the pins for the
xtal-connection and the battery are bended upwards. Then the battery
and xtal are placed atop of the chip, connected to the pins and
everything is covered with a pretty rigid protective compound.
The DS1387 is the same chip with an additional integrated 4K SRAM. All
described modifictions apply to this chip as well.
The only things you need to do is:
- use a Dremel or a metal saw and cut at pin 16 vertically
down until you reach the metal pin surface
- repeat the procedure at pin 20
- scratch off the sealing compound around the pins,
particularly at the No. 16 pin towards the top
- use a watchmaker screwdriver or a nail to break the
connection to battery minus over pin 16
Don't be afraid: this chip is really hard to damage. If you
have a multimeter test the voltage on pins 16 and 20 before and after.
Before it may read anything from some 100mV up to 3V (where you should
ask yourself *why* you wish to modify this chip ...?) and after it must
be 0 (zero) latest after 5 seconds of measuring.
The 0V-reading tells you that you successfully disconnected the
- solder two wires of appropiate length to the pins 16 and 20
- solder a "3 Volt Cell" to the wires.
Care for the polarity ! Pin 16 is GND (-), pin 20 is (+)
This abstract "3 Volt Cell" could be either a battery pack from 2 AA or
AAA cells or a 3V-Lithium coin cell - with holder ! Don't ever solder
directly on a coin-style Li-Cell. It won't do it no good and may result
in early death of that part due to excessive internal heating. Most
likely you won't get a wire soldered properly to it. The case is
usually pretty much "solder-resistive" because of the anti-corrosion
Don't use rechargeable batteries. These are intended
for short-term use with strong charge and discharge intervals - not for
long-term storage with a comparatively small discharge rate. The daily
self-discharge rate on some rechargeables is higher than the current
taken by the RTC.
- maybe use some hot glue to re-isolate the pins and fix the
battery somewhere on the chip
The "appropriate length" bit regarding the wires refers on that
situation where you use a 2-cell battery holder and want to place it
elsewhere inside the computer - further away from the DS1287 chip
Then re-install the reworked chip in the machine - watch out for proper
aligment and position of pin 1 - and reconfigure your PS/2 with its
reference diskette. Should work like a charm.
Some more Feedback !
On March, 23rd, 2007 Chris (xrisl [at]
reported the following:
My old computer has been out of action for months, but this week I got
it going again by following the instructions on your webpage "Reworking
the DS1287 RTC chip".
Without that webpage, I would never have thought of repairing it like
So you have my thanks and gratitude for putting that idea on the web.
(Incidentally, my computer is an Compaq 386N, which seems to date from
On April 24th, 2007 Gary Jay in Ohio, USA
usa.net) reported the following:
Hi Peter...just thought I would let you know that
I got the DS1287 reworking on my first try!
I used an iron file that was about the exact width I needed and just
slowly went back and forth about 50 times until I saw the metal and
then used sandpaper the rest of the way.
Soldered and used a CR2032 battery with holder on top of the 1287.
Worked like a charm and would like to thank you and I am very grateful
I stumbled on your web site. I could not have gotten my Compaq DeskPro
286e back to clock life back without you! Regards, Gary
William Walsh, USA finally succeeded in
the DS1287 rework
His success-story can be read at his Dallas
William Walsh, USA also modified the
The DS1387 is technically near-identical to the DS1287, but has an
additional integrated 4K SRAM. William Walsh did the DS-Rework to
get an external battery to it as well. His report can be found at his DS1387 Rework Page
Really good job, William !
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H. Wendt / pw-software production