PC3086 clock chip replacement
These days, PC3086s are getting fairly old. One of the symptoms of this is the battery in the clock chip failing. If this happens, the message "WARNING: CMOS battery failed" will be displayed at startup, and the computer will not remember the date and time.
Here is how to replace the clock chip:
- Get hold of a replacement clock chip. You need a DS1287 or compatible chip; since the original DS1287 is no longer made, you'll almost certainly be using a compatible part. The DS12C887 (RS Components part no. 343-7360) is a suitable substitute.
- Turn the PC off. Leave it plugged in for a few minutes, then disconnect the power, keyboard, monitor and so forth.
- Open the case. There are six screws holding it together; three on the left hand side and three on the right (there may be one at the centre of the back as well). Once the screws have been removed, the case can be slid forwards and lifted off. Make sure the power button doesn't catch on the case and snap off. The case will remain attached to the computer by wires; there's no need to disconnect these.
- On the left-hand side of the PC, near the back, is the clock chip. This is taller than the other chips on the board. It is marked DS1287 and has a picture of a clock on it. One corner will have a white dot.
- Before removing the chip, make a note of which end the dot was at.
- Remove the clock chip from its socket by inserting a screwdriver each end and levering it gently out. Take care not to break off any of the legs.
- Insert the replacement clock chip, making sure its dot is at the same end as on the original. The dot may be black rather than white. Also make sure that the chip is correctly aligned in the socket with every pin matching a hole.
- Put the PC back together and switch on. You should get a "set time and date" message, but no CMOS battery errors.
- Set a date, switch off, wait a few minutes, and switch back on. The computer should remember the date correctly.