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Removing Socketed BIOS Chips
Most BIOS chips or CMOS chips are in fact removable. Considering the cost of motherboards, it makes sense to fit a socket in case the chip needs to be removed for servicing.
This however is not always the case and you may find your flash BIOS chip or EEPROM is soldered directly to the motherboard.
This does make any repair attempt just a little more difficult and costly, although they can be repaired. If you have a soldered BIOS see this page Soldered BIOS Repair.
Any repair attempt relies totally on the PC makers willingness to provide the needed ROM files for BIOS restoration.
Clearing CMOS after fitting a new BIOS Chip
It is advisable to clear CMOS in the normal manner after fitting a new programmed EEPROM. Some makers insist you do this after updating your bios as a part of the routine. Some boards may not boot until you do this even with a new replacement part.
PLCC EEPROM Removal and Refitting
Before removing the EEPROM, make a note of its orientation in the socket. PLCC chips have one corner removed, this lines up with an angled corner in the socket.
Chip extractors are available to remove PLCC chips and they work very well in most instances. You should in fact use an extractor to avoid damage to the socket. They are easy to use and relatively inexpensive and every budding BIOS engineer should have a PLCC extractor in their tool kit.
Occasionally you will come across a board that has no room around the socket to use the PLCC extractors and an alternative method of removal has to used.
Sometimes when the extractor cannot be used properly you can remove the plastic parts from the extractor to avoid the obstruction.
It is possible to remove the PLCC chips without an extractor but great care has to taken so as to avoid damaging the PLCC socket. Do not lever across the corners of the socket or you may split the plastic casing of the socket itself.
Refitting the EEPROM Is relatively straightforward. Check that the angled corner lines up with the angled corner in the socket then rest the chip in place checking that the pins are all aligned correctly.
Once your happy that the EEPROM is in its proper position on the top of the socket, just gently press the EEPROM down into the socket and then clear CMOS.
DIP-PDIP EEPROM Removal and Refitting
The DIP and PDIP types can easily be damaged during the removal process, and can also be fitted incorrectly.
Taking a photo of your board before removing a DIP type EEPROM is recommended. You can then refer to this when refitting the EEPROM after programming.
There are tools available to remove DIP type EEPROM's from their sockets. I do not use them as the cheaper type will still damage the EEPROM pins if great care is not exercised during removal. If the chip has been fitted in the board for a long time they can be very stubborn and they simply don't want to come out of the socket.
I prefer in fact to use a small wedge or jemmy made from terminal screwdriver to remove this type of chip. You can carefully insert it between the EEPROM and the socket at one end and gently lever up the end of the EEPROM every so slightly. Take care not to stress any other components on the board whilst doing this. Move to the other end of the socket and repeat the process. Keep doing this until the EEPROM pops out of the socket.
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The DIP and PDIP type EEPROM's have a small half moon cut out at one end, and the number 1 pin is usually marked with a small indent. The socket has the same half moon cut out at one end and usually the board is marked with the pin numbers or at least some of them. Normally when refitting the chip it should be the case that these half moons are aligned. However I have seen instances where the sockets have been fitted in reverse.
It is more important to make a note of the chip orientation when removing it, and to make sure the new chip goes back the same way it came out. A photograph taken before removal can avoid a few headaches.
Once you are happy with the orientation of the chip, place the chip in position on the socket to check that all 32 pins fall into there respective positions.
Sometimes you find the two rows of pins are too far apart to fit the socket and the pins need to be adjusted to ensure they line up correctly with the socket. Once your happy that the pins are aligned then you can gently push the chip into the socket.
A short thin steel rule can be a very useful tool when having to adjust the pins on a DIP chip. This can be used by inserted it between the pins and the body of the EEPROM you can then press the pins down firmly on a hard surface using the steel rule. Adjustments can be made by pulling the body of the chip backwards or forwards whilst holding the pins firmly down with the steel rule.