I find using a UV disinfecting lamp for a minute works very good for erasing those UV eraseable eproms.
Though I highly doubt that there is any network card out there that can program those.

in any case,
I think it's best to have a backup of the eproms before you attempt an erase and considering that most bios do run some checksum routine I highly doubt your problem lies with the bios.

the randomness of your described problems makes me think a bad contact/solderjoint or fluctuating power supply.

I also highly doubt your problem is related to a bad BIOS. Bad RAM or a power supply problem are far more likely. If the BIOS has shadow settings, try disabling all of them.

If you need to flash new BIOS roms, do so with a proper programmer. Trying to find a network card that can program the correct size of EEPROM is likely a waste of time and money. Programmers aren't that expensive anymore.

nebular wrote on 2024-07-16, 17:52:

I should try and erase the existing BIOS chips. I already have a florescent UV lamp

It's not just the power but also correct wavelength - which you won't know from cheap UV products. Most non-florescent sources just barely enter the required range, and even florescent ones are usually not great because the UV required is dangerous to eyes and skin, and therefore such lamps are not easily obtainable. The ones that are sold (like "blacklight") are not in range.
I use sun for that. It's free and it works, but it's very much dependant on weather conditions. What some people call "a sunny day" might be useless for the EPROM. Any sort of cloud cover or a typical big city haze can just block most of the UV. So this method is fickle and can take a few days to several weeks (this is also dependent on the particular EPROM in question, the more modern high capacity ones ones tend to be more stubborn for some reason).

nebular wrote on 2024-07-16, 17:52:

Also I don't own a programmer, and currently I don't have the extra money to spend on one that I would only be using sparingly right now.

Then don't even consider any such experiments. You can over-expose the EPROM and damage it. Without a programmer you won't be able to tell how it's progressing, and frankly with such crude methods you want a ZIF socket for the EPROM as well - your chip might be visiting the programmer quite often, daily I'd say if you want to avoid any damage.

nebular wrote on 2024-07-16, 17:52:

I do have a number of network cards that have ROM sockets on them. I've heard that you can program PROMs using those. Does any one know if that can be done with a 27c256 (or it's EEPROM equivalent) and where I could find instructions on how to do that?

The instructions are: Can't be done, sorry. You need over 12V on most (even modern) EPROMs to properly write them, and I don't know any PC card that would allow even 12V switching for this purpose. This requires a programmer of some sort that can pulse the programming pin with correct timing as to not damage the EPROM by writing it too strongly. There might be some NICs that can rewrite a 5V Flash chip, but not EPROMs.

akimmet wrote on 2024-07-16, 19:21:

I also highly doubt your problem is related to a bad BIOS. Bad RAM or a power supply problem are far more likely. If the BIOS has shadow settings, try disabling all of them.

You're probably right. There's no shadow settings for the BIOS so that's not an issue. I'll hook the multimeter up to the power supply and make sure the voltages are all good during startup, but dealing with the ram will be trickier. It's soldered to the board and the chips are in a vertical orientation, so even if I can identify which ones are bad, I'm not sure I'd be able to get replacements. An image of the board can be found here: https://preview.redd.it/hzkniel850tc1.png?wid … e1993b79d75cf78

I'm still concerned that I did something to the board when I removed the original RTC to mod it for an external battery. I couldn't see any damaged traces, but without the service manual or schematics for the board, I can't verify.

It's frustrating. I really wanted to play around with this system more, and when I pulled it out of e-waste it was in pristine condition. The 5 1/4" drive even had the protective card still installed.

nebular, just an fyi, try to measure the +5v voltage on the board in different locations, like the ISA slot, the FPU socket, the simm slot

weedeewee wrote on 2024-07-17, 19:21:

nebular, just an fyi, try to measure the +5v voltage on the board in different locations, like the ISA slot, the FPU socket, the simm slot

Thanks for the tip, I'll do that. I also took a chance at emailing Epson to see if they have the service manual. They still have the user manual and a bunch of product support bulletins hosted at files.support.epson.com/pdf/e2e___/ but not a file index so I can only access what google has listed. It's a long shot, but if I can get the service manual for the board it'll make troubleshooting that much easier.