Heard that those smartphone UV-light sterilizers can erase EPROM for a couple of minutes. Never tried this, as I never owned such a device.

I'm curious about this to. I, admittedly, have yet to absolutely need to erase an EPROM... but I have lots of them, and it would be nice to be able to read them, wipe them and then have them ready to use.

Probably 8 years ago I bought one of the really cheap plastic EPROM erasers that you see for sale everywhere you search for them, and it was horrid. It didn't even work out of the box, and there were components falling apart (nearly shorting other things) when I opened it up. It looked like such a fire hazard I just got a refund since it was broken and never bought another.

I've looked at the name brand ones on ebay but they are ancient (could need new bulbs, repairs, etc.), sometimes huge, and tend to be fairly expensive for a thing that I have yet to really need in 10+ years of intentional retro computing and repairs. I'd grab one for cheap if it came up, but I have a hard time justifying $50+ for something looks like it was abused in a factory for 40 years.

What if you use a magnifying glass to focus sunlight on the photo-sensitive window? Would that wipe them fast? 🤣

Ozzuneoj wrote on 2026-02-25, 07:41:

What if you use a magnifying glass to focus sunlight on the photo-sensitive window? Would that wipe them fast? 🤣

Better off don't try this.

I’m finally ready to share how I solved the problem of erasing UV EPROMs. I initially considered several options, but in the end, I settled on what I believe is the most optimal solution.

Options I Considered

Factory UV Erasers from China: I ruled this out immediately. Too expensive, bulky, and likely unreliable with an unknown bulb lifespan.

UV Medical Lamps: These could be adapted, but buying one specifically for this purpose is impractical and way too pricey.

DIY Erasers using broken DRL (mercury-vapor) lamps: Honestly, this is last-century tech. I didn't want to mess around with something that clunky and dangerous.

DIY Eraser using a Chinese UV bulb for refrigerators: This was my favorite option. It’s a clone of a Japanese bulb and is perfect for a small, compact box that holds a couple of chips. I even bought all the necessary components. It’s easy to assemble—here is a great guide, for example: https://radiokot.ru/artfiles/6467/ (sorry for the .ru link).

Why I Never Built the UV Eraser

The reason is simple: a friend of mine who works at a scrap metal yard hooked me up with a mountain of Winbond W27E512 (W27C512) electrically erasable PROMs. They are perfect replacements for the old 64KB UV EPROMs used in 386 and 486 systems.

There are also convenient analogs for more modern boards. For example, if I need a 128KB ROM, I use the W27C010. For even newer boards, I go with Intel 28 or SST 29 series flash chips (like the 28F001BX-T or SST29EE010), which can be programmed directly on the motherboard without an external programmer. And for XT-IDE, you can easily find the W27E257 (a 32KB electrically erasable ROM) for cheap.

Ultimately, the need for a UV eraser just vanished. My 386, which we restored together, is currently running a Winbond W27E512. Experimenting with UV EPROMs is a total hassle, given the constant cycle of erasing and reprogramming.

My advice to you: Don't torture yourself. Just buy a few Winbond EEPROMs and save yourself the headache!

The right way is a dedicated EPROM eraser. The chips need a specific dose of correct wavelength light to actually properly erase. The cells that hold data are basically buckets of electrons with programming emptying the bucket for a 0, and the erasing process fillsingthat bucket up again to 1... but *only* if done under specific wavelength of light for specific amount of time.

One can use some UV LED or sunlight and get what appears to be an erased EPROM, as in the programmer says it is done, but you hav no real way of knowing if the chip is truly erased since you do not have access to the actual analog value level the sense amps in the chips work with to estimate how full or empty that cell is... and this is important because of data retention time. You can have a chip appear as erased in as little as 5 minutes in a dedicated eraser but when you go into the datasheet of a particular chip you'll find timeframes as long as 45 minutes. This 5 minute EPROM will have data retention time that is far lower than what spec says, maybe just a few years (or even less) instead of decades that a full 45 minute erase will give. In any case the data will not last forever and will fade. It also should be noted that the OTP EPROMs without a window are erased in factory prior to packaging and cannot be erased again without preserving chip reliability afterwards (i.e xrays can recharge a cell, but also cause enough damage the chip becomes essentially unusable afterwards), and the implication is that if that part was made 20 years ago, it has maybe 20 years of data retention life left. (I also received a bunch of OTP EPROMs from my work as part of their cleanup process, I'll put these chips to use but I know they are ticking timebombs).

Also like flash chips, the erasing process actually damages the chip which is why there's a limit to many times the chip can be erased before it becomes too unreliable to function proper. A good EPROM can take a hundred erases, a bad one maybe 10 and the data retention time decreases with each erase as the cells become more leaky. Electrons tunnel out and eventually you're left with a chip that is all zeros... But unlike all the modern SSDs, the cells are ginormous and it'll take a while before the tunneling process has finsihed 🤣

Babasha wrote on 2026-02-25, 07:56:

I’m finally ready to share how I solved the problem of erasing UV EPROMs. I initially considered several options, but in the end […]
Show full quote

I’m finally ready to share how I solved the problem of erasing UV EPROMs. I initially considered several options, but in the end, I settled on what I believe is the most optimal solution.

Options I Considered

Factory UV Erasers from China: I ruled this out immediately. Too expensive, bulky, and likely unreliable with an unknown bulb lifespan.

UV Medical Lamps: These could be adapted, but buying one specifically for this purpose is impractical and way too pricey.

DIY Erasers using broken DRL (mercury-vapor) lamps: Honestly, this is last-century tech. I didn't want to mess around with something that clunky and dangerous.

DIY Eraser using a Chinese UV bulb for refrigerators: This was my favorite option. It’s a clone of a Japanese bulb and is perfect for a small, compact box that holds a couple of chips. I even bought all the necessary components. It’s easy to assemble—here is a great guide, for example: https://radiokot.ru/artfiles/6467/ (sorry for the .ru link).

Why I Never Built the UV Eraser

The reason is simple: a friend of mine who works at a scrap metal yard hooked me up with a mountain of Winbond W27E512 (W27C512) electrically erasable PROMs. They are perfect replacements for the old 64KB UV EPROMs used in 386 and 486 systems.

There are also convenient analogs for more modern boards. For example, if I need a 128KB ROM, I use the W27C010. For even newer boards, I go with Intel 28 or SST 29 series flash chips (like the 28F001BX-T or SST29EE010), which can be programmed directly on the motherboard without an external programmer. And for XT-IDE, you can easily find the W27E257 (a 32KB electrically erasable ROM) for cheap.

Ultimately, the need for a UV eraser just vanished. My 386, which we restored together, is currently running a Winbond W27E512. Experimenting with UV EPROMs is a total hassle, given the constant cycle of erasing and reprogramming.

My advice to you: Don't torture yourself. Just buy a few Winbond EEPROMs and save yourself the headache!

This definitely makes sense. Especially if you have a near endless supply of electrically erasble PROMs on hand.

Still, if someone has the old ones on hand and they want to reuse them, it is good to have some options for doing so. Also, they tend to look a lot different so if someone is a stickler for keeping really old devices looking mostly original inside, they may want to stick to old ceramic EPROMs. I don't think I'm that guy most of the time, but if I had blank old-school EPROMs on hand I would definitely use them when working with old devices that are unlikely to need wiped\flashed ever again.

Tiido wrote on 2026-02-25, 08:46:

The right way is a dedicated EPROM eraser. The chips need a specific dose of correct wavelength light to actually properly erase. The cells that hold data are basically buckets of electrons with programming emptying the bucket for a 0, and the erasing process fillsingthat bucket up again to 1... but *only* if done under specific wavelength of light for specific amount of time.

One can use some UV LED or sunlight and get what appears to be an erased EPROM, as in the programmer says it is done, but you hav no real way of knowing if the chip is truly erased since you do not have access to the actual analog value level the sense amps in the chips work with to estimate how full or empty that cell is... and this is important because of data retention time. You can have a chip appear as erased in as little as 5 minutes in a dedicated eraser but when you go into the datasheet of a particular chip you'll find timeframes as long as 45 minutes. This 5 minute EPROM will have data retention time that is far lower than what spec says, maybe just a few years (or even less) instead of decades that a full 45 minute erase will give. In any case the data will not last forever and will fade. It also should be noted that the OTP EPROMs without a window are erased in factory prior to packaging and cannot be erased again without preserving chip reliability afterwards (i.e xrays can recharge a cell, but also cause enough damage the chip becomes essentially unusable afterwards), and the implication is that if that part was made 20 years ago, it has maybe 20 years of data retention life left. (I also received a bunch of OTP EPROMs from my work as part of their cleanup process, I'll put these chips to use but I know they are ticking timebombs).

Also like flash chips, the erasing process actually damages the chip which is why there's a limit to many times the chip can be erased before it becomes too unreliable to function proper. A good EPROM can take a hundred erases, a bad one maybe 10 and the data retention time decreases with each erase as the cells become more leaky. Electrons tunnel out and eventually you're left with a chip that is all zeros... But unlike all the modern SSDs, the cells are ginormous and it'll take a while before the tunneling process has finsihed 🤣

Wow, I'll be honest I had no idea it was that complex. So you can erase an EPROM and then write to it, but if it wasn't erased "well" then the data written to it won't last as long? That's pretty crazy.

That makes me think the following isn't a great solution... I kinda wish I'd seen your post first. 🤣 I had just typed this right before you posted:

---
While looking around online just now, I stumbled upon this article:
https://blog.j2i.net/2023/08/29/erasing-an-ep … native-devices/

According to this person, by far the best (cheap) method they found was a clam shell UV sanitizer for cell phones. They said that it runs on a 5 minute timer, so it isn't quite long enough, but if you do it twice that seemed to reliably wipe the EPROM he was working with. He said that the one he had is no longer available, but you can now get what looks like an identical device under the brand "Phonesoap".

If you look on Amazon these stupid things are $60-$90 brand new. But, in post COVID19 pandemic world, there are now hundreds of them available for almost nothing on ebay. I just bought one for less than $9 shipped. I am willing to give one a shot for that price. It looks like it could easily hold several EPROMs at once too, it just depends how good the coverage is I guess. The article above said that it ran on a 12v power adapter, but these ones are all 5v, so I'm thinking maybe that was a typo.

Once I get it, I will test it out and post here. If someone else wants to do the same, just search your favorite marketplace\auction site for "Phonesoap" and you'll find scads of them for practically nothing. If it doesn't work at all or works very unreliably, oh well. Not a huge investment and it technically can still be used for its intended purpose.
---

Anyway, order is already placed, so I guess I'll be the guinea pig. Knowing what you said Tiido, I will probably not use this for anything real critical, so thank you for the info. I am curious though, has anyone here ever experienced this personally? Using sunlight or other sources to wipe an EPROM and then having the data later programmed on those chips not last?

appiah4 wrote on 2026-02-25, 07:30:

Any other suggestions?

Most often, a UV-erasable IC can be easily replaced with flash memory.
For example, W27C010
https://www.alldatasheetru.com/datasheet-pdf/ … ND/W27C010.html
If you need to erase chips extra-very rarely, it is easier to buy 10 cheap flash memory chips. And simply replace as necessary.

Back in the old days, last century, I had a need to erase 2532-type eproms. I went to a shop (no internet then), and bought a UV flouro tube and a batten for it. They also gave me some black conductive foam to put the eproms on.

Put the eproms in the foam, on the batten, under the tube, cover it all with a cardboard box, switch on, let it cook for about 20-25 minutes, and hey presto, it's done.

After a number of erase and burn cycles, the erasure wasn't complete, but just leaving the eproms sitting around unused for a few days seemed to let it complete by itself. Not sure how that worked, but it did.

The cardboard box, obviously, was to stop me looking at the light and getting my sight erased.

Most likely, it depends on the region of advertising on Google, but it offers me 1 million offers for UV LED - “manicure lamp.”
As far as I understand, it uses UV-curable photopolymer, so UV is normal there.

appiah4 wrote on 2026-02-25, 07:30:

I occasionally need to blank or re-program EPROMs and I don't have an eraser for this. I tend to just leave them out in the sun and it can take anything between a month to a year for them to clear (for some EPROMs the last few bytes can take MONTHS of baking in the sunlight, sometimes). It's very inconvenient to do this, for obvious reasons.

I was wondering if there are any easy to buy household items I can use for this job? Do thinks like toothbrush UV sanitizers or nail polish curing lamps etc actually work for the purpose? Any other suggestions?

Personally I've tried out using phone sanitisers since they're usually very cheap. Specifically as far as I'm aware you need something that emits UV-C light rather than UV-A.
Nail curing (or soldermask curing) UV stuff is UV-A and doesn't do much to EPROMs. UV-C is not meant to be pointed at human skin and is pretty damaging which is why these sanitiser products are all thoroughly sealed for use.

First I had a go with one that was a white box with a UV-C flourescent tube in it which did work but kinda big.
Then I tried using a HoMedics UV-Clean Phone Sanitiser but it only runs for 30 seconds at a time so requires pressing the go button lots of times - til about 5 minutes had accumulated. And the battery wasn't very good. I had to make a 3d printed ROM holder to reliably get the ROM to stay in place by the UV-C LED in the phone cleaner.

Most recently because the battery was annoying, I tried just hooking my bench PSU into the PCB for the LED, burned one out accidentally and decided to just cut up the PCB with the remaining UV-C LED on it and put some posts to hook onto. With my 3d printed EPROM holder stuck onto the PCB segment I can now just run the bench PSU until the ROM is erased and the design of it means that UV-C isn't escaping far past the ROM's window:

This was used for changing the BIOS on a 286 motherboard most recently, I have EEPROMs but sometimes it's easier to use the original EPROMs, especially now I can reliably erase them with this tiny thing.

Thanks for the explanation Tiido 😀 It makes sense that there would be quite a bit of science in there beyond passing the 'blank check' in the programming software.

I'm curious how well some of the UV flashlights on amazon would work. They emit enough radiant energy to 'feel tingly' if shined directly on skin at short range, and they *can* cure UV resin.

Remains to be seen if they have the needed photon energy to wipe an eprom though.

There are 'room sanitizer' lamps that emit enough UV-C to make a whole room smell 'cooked', that can run for hours.

One of those should surely work.

I tried the 'hacks'; they all took way too much time. I tried two purpose-built erasers; they both broke for no apparent reason. Finally, I bought a germicidal UV-C bulb that goes in a standard bulb socket, for like $15, and erasing EPROMs is a nonissue. I switch it on for 5 minutes down in the basement, so I don't have to smell the ozone, with a cardboard box covering it to prevent eye exposure.

I use a UV sterilizer designed for pacifiers. It is a little awkward since it has a set timer, so i have to repeatedly reset it to fully erase an EEPROM. But it does work.

bakemono wrote on 2026-02-25, 15:06:

I tried the 'hacks'; they all took way too much time. I tried two purpose-built erasers; they both broke for no apparent reason. Finally, I bought a germicidal UV-C bulb that goes in a standard bulb socket, for like $15, and erasing EPROMs is a nonissue. I switch it on for 5 minutes down in the basement, so I don't have to smell the ozone, with a cardboard box covering it to prevent eye exposure.

If it can go in a standard edison socket, then why not use a metal parabolic, face-down on a table?

Back before I got an eraser, I tried sunlight (non-magnified) for days with no success other than erasing them enough to make them unreliable.

You really need a UV light - some "blacklights" can work.

I made my first UV eraser (which I still use) using a florescent "bkacklight" tube in a plastic box which suspended it over the EPROMS.

At some point along they way I got a "Radio Shack" one which was essentially a smaller version of the same thing. I still use the homemade one more because it has a mechanical timer to turn it OFF.

wierd_w wrote on 2026-02-25, 15:21:

If it can go in a standard edison socket, then why not use a metal parabolic, face-down on a table?

The bulb I have is about 7 inches long, so using a horizontal orientation allows lining up a whole row of chips underneath. Mounting the bulb in a hood to prevent incidental exposure is possible but would require a relatively large/deep hood.

They DO exist..

appiah4 wrote on 2026-02-25, 07:30:

I occasionally need to blank or re-program EPROMs and I don't have an eraser for this. I tend to just leave them out in the sun and it can take anything between a month to a year for them to clear (for some EPROMs the last few bytes can take MONTHS of baking in the sunlight, sometimes). It's very inconvenient to do this, for obvious reasons.

I was wondering if there are any easy to buy household items I can use for this job? Do thinks like toothbrush UV sanitizers or nail polish curing lamps etc actually work for the purpose? Any other suggestions?

I've had good luck with a UV sterilizing lamp. you can find those in some swimming pool accessories that let the water that goes from/to the filter pass by the lamp first.
smaller UV sterilizing lamps also exist in some airconditioning or air filter units.
When you go for something LED based it's good to know that if the LEDs aren't in a metal case that they won't produce the good UV for erasing the eproms.
the reason for them being in a metal case is that the UV also destroys the plastic casings.

When using a UV sterilizing lamp, half a minute to a minute and a half is more than enough to erase the eproms.

WARNING, in case you didn't already know. the UV wavelength required to erase eproms is dangerous to skin & eyes. long term exposure will make you suffer. like welding without safety glasses.

which reminds me. if you have a welder, you might try to put your eproms near to where you are welding, directly exposing the light of the welding to the eproms.

I use the tube from an old broken mercury vapor lamp. These are used everywhere, like street lights. They have an inner tube that is quartz, and and outer tube that is glass. Quartz is fairly clear to UV (amorphous glass is not), so I take the small inner tube and hook it up to a high voltage laser driver. This is not very bright, maybe 1w. One of those old neon sign transformers would work too. This will erase a chip in a few minutes. I basically expose them until they show erased, then give them a couple more minutes. Note this is NOT hooked up to the 400w ballast that normally drives these bulbs. I have not tried it, but that should work even quicker... I've never noticed bit rot with these chips. The ECU in my car has one in it that was erased and programmed 25 years ago.

So this was re-purposing junk I already had. If you're going to go buy something, an EEPROM seems like the way to go, as others have suggested.