BIOS repair example BIOS chip physical damage

Computer shop news One day, the old customer came to the phone and told his unit that the small LAN damaged three motherboards due to frequent power outages and asked for help. So I immediately dispatched it. After arriving at the scene, I checked it by the replacement method and found that there was a problem with the BIOS of the motherboard. The hot plug method is not valid, and it is determined that the BIOS chip is physically damaged.
The motherboard they use is a brand-name integrated motherboard, the CPU is P120 (old enough), and the motherboard BIOS chip is Intel's P28F002BX chip, which is a 2Mbit chip. Tested with the programmer, it was found that all three chips have different degrees of damage and can no longer be used. Since this chip is no longer available, it can only be used with the existing Winbond 29C020 on hand. Use the programmer to read the data of the good chip and write it to three AT29C020. Unexpectedly, when the written chip was inserted into the motherboard, the power-on boot did not respond, and the repair was not successful. Graphics card failure 28F002BX is Intel's first generation of erasable BIOS chip, its internal data structure is block (as shown). The BOOT BLOCK block stores the BIOS basic boot information. It supports the ISA form of the graphics card. When the BIOS upgrade fails, the BIOS can be booted and repaired from the BOOT BLOCK. This design idea has been adopted by the BIOS refresh program and continues to this day. When erasing, 28F001 is the minimum modification unit of Byte; when writing data, a certain programming voltage is added to the chip, and the erasure of the data in the BOOT BLOCK block is added with a specific erasing voltage.
29C020 is Flash ROM (flash ROM), belonging to single voltage chip. The biggest difference between the Flash ROM and the EEPROM chip is that no specific programming voltage is required when deleting data. In addition, when deleting the data, the Flash ROM does not use Byte as the basic unit, but uses Sector (also known as Block) as the minimum unit. The size of the Sector varies from vendor to vendor, and is only written in Bytes as the smallest unit when writing.
In the past, there were 27 series chips on the motherboard. The 27 series chips belong to the EPROM, and the data in them are erased by the ultraviolet radiation emitted by the EPROM eraser (EPROM Eraser), and the dedicated programmer can be used to rewrite the data and write to the chip. A certain programming voltage must also be added to the content.
On the motherboard, the BIOS chip is only in the state of reading data. From the principle analysis, the chips of the 27, 28, and 29 series can be replaced. If the factors of the upgrade are not considered, the three are compatible. Therefore, I suspect that the problem may be that the motherboard is too old and does not support the chip refreshed by page, that is, the old motherboard and the new chip "when the door is improper, the household is not right". I found a piece of 28F020 (also an old-fashioned one, and now I can't find it on the market). I swiped the program on the programmer and plugged it into the motherboard. The boot returned to normal and confirmed my guess. In order to further confirm the correctness of the above analysis, a 27C020 write program is used, and after plugging into the BIOS socket on the motherboard, the power is turned on and the machine can work normally. This indicates that the motherboard does not support the new chip.
Although in theory, the 27, 28, 29 series of chips can be substituted. However, in practical applications, it should be noted that some motherboards may not be well supported for some types of chips due to design reasons. If this happens, you can find different types of chips and try several times.