Is it safe to replace the TMS27C010A-12JL EEPROM with a flash bios chip like the MX28F1000PPC ?? Or the motherboard would only take the eeprom chip?
I looked at a couple datasheets (they can usually be found pretty easily by searching the part numbers).
The MX28F1000PPC pinout matches the 27C010 and it runs on the same voltage in read mode (5V). It would most likely work.
One small difference at pin 31. On the MX28F1000PPC, this pin is required to be held at Vih (5V) while reading. On the 27C010 it's "don't care". This means your motherboard might not hold it at 5V as you need it to.
You can use a multimeter to check voltage on pin31 while the system is running, if the system is holding it at 5V then it will meet the requirement of the MX28F1000PPC.
EPROMs and Flash ROMs don't behave exactly the same, but they're very close. I've run into a case where a seemingly compatible Flash ROM did not work in place of an EPROM, but I think that's rare. Given that the pinouts are electrically compatible, there's no danger in trying it.
Windowed UV EPROMs are EPROMs (one E). EEPROMs (two Es) are "Electrically Erasable", which windowed EPROMs are not (they require exposure to UV).
I'm not sure whether Flash ROMs are technically supposed to be called EEPROMs or not. I thought EEPROMs were classified as a separate type, but I haven't looked much into that subject.
"27" series chips are UV EPROMs. I thought "28" series chips were classed as EEPROMs and "29" series as Flash, but the 28F1000PPC datasheet I looked at is calling itself "Flash". I don't know if they're taking liberties with the terminology or I'm just wrong about there being a distinction.
When you expose an EPROM to UV it resets the bits to "1" values. The programmer selectively sets bits to "0". The way the bits are stored is analog in nature (that's how the world really works), so a badly erased or programmed chip might not give consistent reads in different devices or it might corrupt in less time than a well programmed one.
When you erase a UV EPROM, you should clean the window with alcohol so that it gets good exposure evenly across all the memory cells. If you leave sticker goo on the window then some parts will be harder to erase. When this happens with a real eraser, it can lead to the user extending the erase time and overexposing other parts . Overexposure can make some bits become stuck.
I've read internet comments that you can erase an EPROM by leaving it in the sun for a few weeks. I've never tried it though, and I'm not sure how many of the people who say this have tried it either. I'm sure it works, just no idea how long it would really take. The more directly it's exposed to the sun, the better.
A few years ago I found an old US-made eraser with a metal chassis on eBay for about $30-$35. I think new Chinese ones are routinely available at that price, and that's probably a fine way to go. Due to paranoia about UV exposure I dug to find one from a company with a reputation and address, but I was probably worrying too much. 😀
EPROMs are all out of production as far as I know. Many older devices use them so there is a demand for them. Old arcade game PCBs use tons of them, and that's a high maintenance hobby.
Pricing on eBay can be inconsistent from one part number to the next, it depends which part numbers are flooding the market while others are harder to find. Sometimes substitutes with larger capacity than needed are cheaper than a match to the originals.