Fail Of The Week: EPROMs, Rats’ Nests, Tanning Lamps, And Cardboard On Fire

It all started when I bought a late-1990s synthesizer that needed a firmware upgrade. One could simply pull the ROM chip, ship it off to Yamaha for a free replacement, and swap in the new one — in 2003. Lacking a time machine, a sensible option is to buy a pre-programmed aftermarket EPROM on eBay for $10, and if you just want a single pre-flashed EPROM that’s probably the right way to go. But I wanted an adventure.

Spoiler alert: I did manage to flash a few EPROMs and the RM1X is happily running OS 1.13 and pumping out the jams. That’s not the adventure. The adventure is trying to erase UV-erasable EPROMS.

And that’s how I ended up with a small cardboard fire and a scorched tanning lamp, and why I bought a $5 LED, and why I left EPROMs out in the sun for four days. And why, in the end, I gave up and ordered a $15 EPROM eraser from China. Along the way, I learned a ton about old-school UV-erasable EPROMs, and now I have a stack of obsolete silicon that’s looking for a new project like a hammer looks for a nail — just as soon as that UV eraser arrives in the mail.

Flash from the Past: UV EPROMs

Old-school EPROMs are made by laying out a bunch of field-effect transistors (FETs) in an IC. In read mode, a gate voltage is applied to each transistor, and whether it conducts or not determines if the bit of data stored there is a one or a zero. The gimmick is that an additional metal layer — the floating gate — is interposed between the FET’s channel and the gate. Putting a negative charge on this floating middle layer will raise the voltage required to turn the transistor on from the outside. A bit of info can thus be stored in the physical form of excess electrons on the floating gate.

In a UV EPROM, the floating gate is insulated all around by an oxide layer, so it retains this negative charge essentially indefinitely. You get extra electrons onto the floating gate through “hot-electron injection”: applying enough voltage across the floating gate that electrons jump through the insulating layer. When reading the data, transistors that have a negatively charged gate won’t conduct at their normal gate voltage, while those that haven’t been programmed will. Easy peasy.

But then how do you get rid of the excess floating-gate electrons in order to blank an EPROM? The original method proposed to erase ceramic-encased EPROMs was to use X-rays in a 600° C oven, but cooler heads prevailed and chipmakers instead installed a relatively expensive crystal window that’s UV permeable, allowing longer wavelengths of carcinogenic light to coax the electrons back into the substrate. Apparently, in the 1970’s hard-UV lamps were commonly used for their germicidal effects in barbershops and the like, so having a UV-erasable EPROM was convenient. My own attempts to clear UV EPROMs have been anything but.

How Not To Clear an EPROM

I ordered a ten-pack of used (!) 27C160 UV EPROMs online and was a bit surprised when only three of the ten arrived with the memory cleared. Unless I could figure out how to blank a UV EPROM, I would only have three chances to flash my synth’s EPROM. And since I had a ROM dump with 16-bit words of unknown endianness, there was a 50% chance that I’d need to try twice. This left me with only one EPROM to use in developing an EPROM programmer. So I decided to see if I could erase them to provide myself with a safety net.

I have read, in these very pages, tales of success erasing UV EPROMs with a UV LED and by harnessing the power of the sun. My EPROM’s datasheet specifies “wavelengths shorter than 400 nm” and recommends “30 to 40 minutes using an UV lamp with 12 mW / cm2 power rating.” It also suggests that approximately one week of exposure to direct sunlight would suffice. So these Hackaday stories sound plausible on the surface.

Maybe November sunlight in southern Germany doesn’t pack the same UV punch of full summer in southern California or wherever the datasheet was written, but the two chips that I left out on our balcony displayed exactly the same data after a week of exposure as they did beforehand. Not a single bit flipped, and there were four fully sunny days. Maybe it was the cold? I asked around Hackaday HQ, and Jenny said she’d tried once and it took three weeks or more over an English summer. This was clearly not the quick way to go.

So I tried a random UV LED from my junkbox, and got nothing. True UV LEDs are difficult and expensive to make, and this one was very visibly blue. So while it was failing to erase an EPROM on my desk, I mail-ordered something that stood a better chance of doing the trick: a $5 375 nm Nichia UV diode. It’s a 6 mW device at 375 nm,  instead of the 12 mW at 254 nm that mercury-based germicidal bulbs use, but it was the shortest wavelength I could get for a reasonable amount of money, and the datasheet says “under 400 nm”, right?

Well, kinda right. The good news is that bits were flipped. After 24 hours, some 10,000 bits read out as ones that had previously read as zero. The bad news is that there’s a big difference between an EPROM that has flipped a few thousand bits, resulting in corrupted data, and one that’s lost all 2,097,152 bits and is a clean slate.

From datasheets, the exposure curve is supposed to be S-shaped: a first very few bits flip, then most do, and then after a while the last reluctant bits give in. With the promise of this avalanche of ones, I left the LED running at 15 mA, the rated current, for four days. Each time I checked up on the chip, it made progress, but it was slow progress. Compared with a promised 40 minutes in a proper UV eraser, this was taking far too long. It’s also possible that these used chips are somewhat worn out and will require a little more persuasion anyway.

And Then I Set Things On Fire

And then it struck me! My mother-in-law stashed her old tanning lamp in our basement about seven years ago, where it’s been taking up space and collecting sawdust ever since. Tanning lamps run on the same mercury UV bulbs used in the germicidal lamps, but they spread the UV out over a much wider area — a human body. If I could get an EPROM up close enough to the bulb, though, it just might work. So I grabbed some cardboard to use as backing, taped an EPROM directly to the lamp, and fired it up.

I have since learned that tanning lamps also have a large IR heating element to simulate the warming effect of the sun. Taping cardboard to the sun is not recommended. After five minutes, my wife asked me what smelled like smoke, and I started running downstairs. When I arrived, there was a hot broken EPROM on the floor, and she was stomping out the cardboard fire. Dramatic! We aired out the house, and I placed an order for one of the $15 import EPROM erasers that evening.

Not to be beaten, I also fabricated a frame from aluminum that could hold an EPROM against the tanning lamp’s shield, but after three 30-minute sessions not a single bit was flipped. The UV in a tanning lamp is probably either filtered or defocused enough that it’s safer for human skin and not suitable for clearing EPROMs. Anyway, it’s not putting out the 12 mW / cm2 that I need. So the cancer machine in my basement continues to be an albatross around my neck.

Programming EPROMs is Refreshingly Easy

I embarked on this EPROM-clearing journey because I only had three blanks out of ten ordered from eBay. Luckily for me, programming them turns out to be as easy as reading the datasheet and following the instructions. Basically, you’ll need a source of oddball voltages for programming the EPROM: 12 V for the hot-electron injection, and 6.5 V to provide a little margin during verification — if the FET won’t open at 6.5 V, it surely won’t open with the nominal 5 V operating voltage on the gate. Finally, you need a way to set up the chip’s address and data pins, but this is no big deal if you’re handy with a microcontroller.

My old synthesizer used 27C160 EPROMs, one of the last types of chips to be made before EEPROM, with an extra “E” for “electrically erasable” memories took over. As such, the 27C160 can store a still-impressive 2 MB, addressed as 1,048,576 16-bit words. This means that it has 16 output pins and 20 address pins, plus two more that need to be strobed to flash and verify the data respectively. That’s a lot of GPIO!

I have a few budget black STM32F407 breakout boards that I use for high-GPIO-count projects because it has three ports of 16-pins each that are essentially free for use and that means that I didn’t have to think hard about where the bits go or hook up shift registers. EPROMs are designed for old-school TTL logic levels, so you can even use a 3.3 V microcontroller without level shifters!

The firmware I used was equally simple, just reading in a value over the serial line while counting up the addresses and setting it up on the GPIO pins. Toggling the verify pin makes sure that the intended value “took”. I love writing up simple projects like this in Forth, because I can write and debug the code interactively and then automate things by sending the same text commands over the serial line from my laptop, where I can script up the hard stuff in Python. So the laptop-side code sends something like 12345 000000 program over serial, and the Forth system automatically returns an “ok.” when it has programmed and verified that word. Each word took just about 15 milliseconds, which doesn’t sound bad until you multiply it by a million and get something like 4.5 hours. Oh well, I was just going to program one. Or two, if I messed up.

It’s ugly, but if you want to take a gander it’s up on GitHub. It’s easy.

In the end, I managed to code and verify my programmer firmware using only a single chip, which left two more blank EPROMs to burn one ROM image. Of course, Muphry’s Law struck, and the OS ROM data I found on the Internet was stored big-endian, and I had initially guessed at little-endian, so I got to burn the last blank EPROM that I had left.

Hammer Seeks Nail

EPROMs are appealing in their simplicity. Unlike a modern, two-E, EEPROM there’s no protocol of any sort here. Simply impose voltages for an address on the pins and a decoder sets sixteen FET gates, and some of these tiny FETs open while others don’t. All of it happens within a few tens of nanoseconds. Any pattern of 20 bits can be mapped to any pattern of 16. That’s memory!

Now what am I going to do with the remaining EPROMs once the UV eraser arrives? Their longevity and moderate obscurity might make one a good place to store secret key material. Maybe I’ll stash an EPROM with my GPG key in the safe deposit box along with the paper printout? Or use them as secret decoder rings for über-retro-nerds? Or maybe fetch some old, and historically accurate, drum machine samples and burn them in to recreate a LinnDrum? Hook up a ladder-DAC and build a 16-bit resolution arbitrary waveform generator? Sixteen outputs suggests a sixteen-segment display lookup table to me, but with a 20-bit address space I’d have room for every possible glyph 16 times over. That seems ridiculous.

What would you do with a small pile of EPROMs? And how would you erase them?

[Epilogue: The $15 UV eraser arrived, and did exactly what it should, in 15 minutes, and nothing caught on fire.]

86 thoughts on “Fail Of The Week: EPROMs, Rats’ Nests, Tanning Lamps, And Cardboard On Fire

  1. If I had a big pile of EPROMs, _and_ had my act together, I’d back up all the EPROMS in all of the computers, printers, and test equipment I have laying around the lab, er, house.

    Problem is, there are at least 8 different EPROMs I’d need to have a programmer/reader for. The 27Cxxx are not too bad, but the 1702’s and others of a similar age (in the Altair 8800 and 680b) require some really odd voltages and timings. Of course, one can make adapters, etc, but that leads to a whole ‘nuther list of projects!

    1. For the record, one can avoid all the “fun” dealing wth ancient eeproms, just because more modern flash ROMs like 29Fxx and so on are backward compatible. So one can just flash the thing more usual way and put it into 27C socket. The only difference is when you about to program that thing, but reading is pretty much the same.

  2. Anything “before” a 2716 starts getting into increasingly weird voltages and algorithms, and even a 2716 took 25V as I recall to program. You are unlikely these days to find an off the shelf relatively modern programmer that will do anything pre-2716.

    Don’t forget to put _very_ opaque tape over the window of a UVEPROM. A bright light or (definitely, big fun) laser pointer will cause an immediate software upset.

    1. _very_ opaque indeed.
      I worked on a college project seemingly a hundred years ago that used 2716’s. We took some photos to include in the lab report and the flash did a nice job of corrupting the contents of the EPROMS.

      1. Yep that is what I used. Got real good with micro printing the file name and revision of the code on that label. Only a PIA to make one mistake in the code and have to wait 15 minutes to cook your eprom!

  3. You can use EPROMS as logic devices. You input a particular bit pattern on the address bus and you get a corresponding bit pattern on the data bus. You can use static logic tables to make a poor mans PLD.

    1. I did this back in 1999 and developed a test circuit for Minibar shelves using some odd bits I had lying around.

      The shelves had IR emitters and sensors to detect things being removed and had to be tested in the factory at different distances as different bottles had different shaped bottoms so had different criteria.
      An Eprom was programmed to provide an output on the data bus if a fault condition was detected (i.e. the input address was invalid).

      Just had a reminisce and found my old design notes with the code I programmed.

      Tens of thousands of these boards were quickly tested and as I incorporated a buzzer on one of the outputs, we were able to test a complete shelf in seconds.
      Previous to this, it was too easy to miss the odd LED output indicator or misinterpret the output at a particular level.

  4. A 9W UV fluorescent sterilizer tube, as used in air duct or water (aquarium) sterilizer systems works well. $8 on Amazon. Takes a normal fluorescent ballast, as found in CF fixtures, or “UV” bug zappers (which won’t work: wrong wavelength). Don’t even think about looking at it with bare eyeballs.

    You can use an EPROM as a waveform table for a discrete Direct Digital Synthesis waveform generator. 20 years ago that might have made sense, but almost pointless now: faster ones are already on integrated DDS chips.

    1. About 20 or so years ago I made a DDS just like that .
      It used 2 EPROMs, one to hold the wave table and the other converted the address to drive the LED frequency display.

  5. These “sun simulators” run the mercury lamp at a rather high power. This raises the temperature and therefore the pressure inside and allows the mercury to absorb it’s own hard UV. By switching out the heaters with a high(er) value resistor you can get it to emit hard UV. Doing so you should be REALLY careful, those things can give you cancer or others nasties in a real hurry.

    1. I have a friend that in the 90’s used to erase his eproms via a small uv tube in his desk lamp.. placed very close to the chips. The thing is you can be careful and avoid the uv but they also output ozone which is a gas. Needless to say after a heavy weekend hacking a project with annoying bugs the room had a definite storm like smell. Next day heavy drowsiness and headaches put us on alert and some reading into ozone effects. It’s deadly! Definitely leave the window open and stay out of it if doing lots of erases.

  6. [Elliot]
    Paragraph 10 (the one with the UV diode link) has
    “It’s a 6 mW device at 375 nm, instead of the instead of 12 mW at 254 nm mercury line that germicidal bulbs use,

    You or another HaD editor can fix that.

  7. Somewhere I got hold of a germicidal bulb (maybe 10 inches long) and a fixture with starter for it and have been happily erasing EPROMs ever since. Actually I haven’t done much of that in the past 5-10 years, which is fine by me. I mounted the whole thing in a plastic case intended for some long gone power tool that I found in a thrift store. Works great. That short UV is bad for your eyes. I use my old Gra-Lab darkroom timer to time the process. It seems like anything over 30 minutes works.

    I did have a board for a MC68010 based device sitting next to a window for years. And lo and behold I went to boot it up and the ROM’s had been partially erased. I wouldn’t call it erased, simply corrupted. I had burned those roms and never placed any kind of cover/label over the window. But I had the hex files and could just burn new ones and apply labels.

    1. During a COMDEX show (late 1980’s?) when many companies were producing their own IBM clones, some marketing people thought the motherboards “looked better” without the covers on the EPROMs. Some of those clones crashed every time a camera flashed nearby.

  8. In the 1980s I erased EPROMs with direct sunlight, also in Southern Germany. But it was in summer. It took around 10 to 14 days when the weather was fine. So, in November you probably have to wait until February but it works ;-)

  9. Best idea yet: at CCC, I was talking about EPROMS with someone (say hi, b/c I forgot your name) about those linear cellular automata. We realized that you could implement one in an EPROM: each address is the current state, maps to the next state in memory, feed back into the address. Clock as fast as you dare. :)

    With the 16-bit 27C160s I’ve got, that’s 16 cells per EPROM, but there are enough extra bits in the address space to chain them together side-by-side. Rule 110 POV toy here we come!

    1. That would have been a good idea! The sad truth is b/c I would have had to open the device, and it’s held together by like 20 screws.

      But that’s just laziness, and I had to open it eventually anyway.

      FWIW: I did also dump the older OS ROM just to see what’s different. It’s far too much to be worth the casual look that I was willing to put into it.

  10. Going the other way, our hackerspace has been using an old EPROM eraser as a curing-lamp for 3D prints after removing them from our resin machine. :) It’s a bit more predictable than sunlight during a Michigan winter, and more friendly to us night-owls.

  11. Just put your eprom in your laser engraver and vector print a circle over the window. Or buy a proper eraser. Back in the day I had the proper eraser. However my programmer topped out at 32’s if I remember correctly. For anything bigger I had to bend the address leads out and use clip leads to make multiple files. Reading and writing big chips was a bit of a pain, but for the limited number of chips we did it worked and saved us some money. The company I worked for at that point in time had a few K invested in their programmer. We were in for under $100.

    1. I used UV EPROMS in companies I worked for from the end of 1980s through the early 2000s. The 6.5V Vcc was not required for EPROMs bellow 27C64, that’s the difference. If I recall well, introduction of elevated Vcc was marketed as optional “fast programming algorithm”, so at first 8kB EPROMs could be programmed using similar algo to older ones. I suppose later when fast programming became the norm and new device programmers all supported it, EPROM manufacturers dropped the support for the old ones, or simply used a larger capacity device dies in smaller capacity device packages for economies of scale reasons. Once the miniaturization advanced far enough, I guess there wasn’t much difference in yield between a tiny and a tiny tiny chip.

  12. If you have a pile of worn out, damaged, unprogrammable etc EPROMs, daisy chain the GND and VCC pins together and make Photovoltaic power supply – for very low power projects.

      1. No idea how much current or volts. Put one under bright light and measure the output. I know someone who did that with a bunch of BIOS chips from dead motherboards as a science project back when he was in high school. IIRC he less than one volt, don’t recall how many chips he strung together.

        Usual power rules should apply, series to increase voltage, parallel to increase current. Figure out how large an EPROM grid it would take to charge a single 1.2V NiCd or NiMH cell.

    1. Yeah. I would have tried one out, but I just didn’t have one. I think they use LEDs similar to the one I tried, though.

      Which is to say that any of the LEDs that are skin safe are probably also a higher wavelength than the germicidal / EPROM-eraser lamps.

  13. i have a “hi-lo systems all-11” vintage programmer which crunches even through antique (21.5V programming voltage) chips. very useful if you also still use commodore 64 and such… some commercial radios can be converted to ham aswell that way (with a bit of other digging) and i guess the cb radio eprom mods are known. AND – a “burned” eprom will prevent any viruses that want to settle in the UEFI code, as theyre not onboard programmable. most common chip around here is the 27C512 btw.

  14. i’ve seen pinball machines with an eprom with open window very close to a fluorescent tube that has been shining on to the chip for thousands of hours. All bits still there but I covered them up with alu tape.

  15. My eraser consists of a portable cash/note check lamp fitted with a germacide bulb from the local aquarium shop.
    At the time, I think it cost all of £10.
    Harder now as note check lamps are probably all LED based, but I think you still get the mains operated ones easily surplus.

    Why not use EEPROMS in your instance?
    The 29F1615 was pretty much the drop-in alternative to the 27c160. (Unless access time was an issue 90ns vs 70ns)
    There’s a pack of 3 on ebay for $5.90 w/free postage.

      1. I’ve never found a list. This was found via a mooch for 16Mbit EEPROM’s – suprisingly few that are parallel _and_ DIP.

        You may find or roll together a PLCC or TSOP to DIP adapter.

  16. The 600C thing isn’t quite right. The actual reasoning is, that while X-rays would’ve wiped the EPROM, they would also have knocked some atoms out of place in the silicon, which might’ve caused undesired effects. So the 600C (actually 450C up to the melting point of silicon) is to anneal it, let the silicon atoms flow back into a more relaxed state.

    I got that from the link on Wikipedia, from the bit of text you quoted from there. It led to Jed Margolin’s website, strangely enough, which I was sure I’d been to before. Turns out he was an old programmer at Atari. Which I never was, but I’m a fan of their computers and games.

  17. Always believe the datasheet.

    Just don’t assume you understood what they meant. It may be that they meant 7 days * 24 hours at the equator, and you’re supposed to normalize that based on your location, season, and weather.

  18. You really need a 254 nm mercury tube (UV-C, a germicidal lamp with a quartz tube) for this to work properly.

    Longer wavelengths, used for nail acrylic or photolithography or blacklights or similar, won’t work well.

    If it burns skin and eyes, breaks DNA, kills cells, generates the smell of ozone, and has UV danger warnings… it’ll work.

    Recommended erase dose is given in the typical device data sheet here:
    http://media.digikey.com/PDF/Data%20Sheets/ST%20Microelectronics%20PDFS/M27C512.pdf

    These lamps are still routinely sold… they are used in all Class II biological safety cabinets for example, for disinfection.

  19. It would be nice to have a modern design for an EPROM programmer.
    Low cost, simple, minimal BOM, compatible with modern PCs. (USB, not parallel port). DC-DC converter to allow Vpp generation from only USB power.

    I wonder if such a thing exists?

    1. I had to spend a few $ on a cheap EEPROM programmer that plugs directly into a USB port. Only used it to directly program one BIOS chip for a motherboard that had the unfortunate tendency to brick itself when using its built in BIOS flashing. There was no DOS or Windows flash program provided for it and IIRC the Award or whatever brand it was flasher software wouldn’t work on the board.

      So I tried updating it, bricked it, bought the programmer. A week or so later I had the programmer and flashed the last BIOS update directly to the chip. Still have the programmer, somewhere.

  20. Maybe I’m wrong but all my test were made with UV-C tube (really dangerous those are germicidal tube) tanning tube on other hand are UV-A and UV-B source, what you find in our atmosphere, UV-C from the sun are blocked. It would explain why your tanning machine failed to erase anything.

  21. Re: burning cardboard

    Many years ago, when I was a young engineer, I worked at Data General in Westboro, MA. We shared lab space with a number of groups, one of which was developing something new, which had been failing when it got hot. They thought they had a fix, and decided to test it by making a cardboard heat chamber and letting it run overnight. They may or may not have added a heat gun to the setup.

    I arrived early the next morning and noticed the office area smelled…funny. And there was this greasy black dust all over everything. Then, I went out to the lab. The device in the cardboard heat chamber had burned up, taking a printer with it. The greasy black stuff was the burned up urethane housing of the printer, which had been spread throughout the building by the HVAC system. No sprinklers had triggered. And, of course, the greasy black stuff was conductive. Not good in an electronics lab. We spent quite a while cleaning the stuff off all our equipment.

    Someone finally figured out that breathing that stuff wasn’t very healthy, and they sent us all home for the day. What a mess.

    Cardboard is for shipping boxes, not for thermal testing.

  22. I routinely used a 125W or so mercury streetlamp stripped of the outer glass shell coated with fluorescent phosporus which gets exited by the primary UV mercury emision. This can be done VERY CAREFULLY wraping the lamp in a thick cloth and hammering ever harder until it cracks, exposing the inner quartz tube. The outer glass is not presurized or vacuumed so there is no blast risk.
    This type of lamps I used for ereasing Eproms (5 – 10 minutes at 5 cm aprox) as well as exposing photoresist for prototype pcbs I kept doing myself until quite recently. Just made a simple aluminium parabolic reflector – cover and that was it. Keep ventilated, it smells ozone.

      1. But effective – and available even after the bubble wrap regulations make the other stuff harder to get. I’ve also used that trick. It’s a fantastic light source for the older UV-only presensitized PCB stuff you’d get from GC chemicals and others – enough short UV to contact print through a window glass frame (that eats a big piece of short UV energy, but hey, there’s plenty).
        Interestingly, when new these produce so much ozone (or at least mine did) that I couldn’t really use it indoors unless I put it in a box with argon or nitrogen (I’d have a link to my old web stuff but this place doesn’t like links much). After awhile (maybe a few hours of use), it stopped making so much ozone (it “solarized”), but still made enough short UV for the intended purpose as well a erasing EPROMS quickity-slick, you betcha.

        Warnings about eyes – it doesn’t look nasty at all, till you look away and are somewhat blinded…the bad stuff you can’t see! I’m not normally Mr Safety and found out the hard way.

  23. I once converted an old tanning lamp as a PCB exposure lamp:
    I removed the IR element and replaced it by two parallel connected ballasts for 60W fluorescent tubes mounted in a wooden box which also doubled as the base of the device. The lamp was mounted facing downwards. Then I also removed the adjustable glass filter tube around the high pressure mercury bulb. The mechanical timer from an old toaster completed this.
    This setup worked quite good, except the strong smell of ozone. Which let me wonder how anybody wanted to voluntarily irradiate himself with this lamp with or without the filter. I preferred to leave the room during the exposure.
    I also used this lamp for EPROM erasure by placing the part about 1-2cm below the lamp for 20 minutes. The ceramic package got probably above 100°C but the part was erased.

  24. Take one of Thaise halogeen bulbs that have a small bulb inside a larger glass enveloppe. The Outer envelope has a uv blocker, so Break and remove it. The inner bulb produces plenty of hard uv radiation.

  25. The company I work for had been using ST Microsystems UV erasable ceramic 27C512 eproms till maybe 2016 when we switched over to OTP eproms by Atmel due to not wanting to pay for the still available military grade versions. Recently the only maker of the mil-spec parts or the only ‘new’ supply left that I could find is Microchip. New in this context is that it is still available from a vendor who is authorized by Microchip, still has a stock of the new parts and has an allegedly secure distribution channel to the end user. The device we make is what was called in the 1990s a human machine interface, it accepts limited configuration on how to display data from a programmable logic controller. It has a huge 2 x 20 VFD and a blizzard of buttons done via an older screen printed technology adhered to an aluminum plate. All of the components are attached to the metal plate on threaded studs using metal standoffs and yes it has metal BOLTS and washers. It also has a 32k flash chip for configuration that at one time cost more than every other part including the 3A AC/DC power supply. We have a few customers left who still pay us very well for this.

  26. You can have a small 4W germicidal lamp for about $25, which is sufficiently large for erasing 4-5 EPROMS at the same time. I erased about 200 EPROMS this way last year. Just go to any shop where they sell bulbs or aquariums.

  27. I loved this article and laughed my ass off. I first worked with eproms about 35 years ago. (yes I know I’m old) When I built an eprom programer on a Timex Sinclair platform. I never could get them to erase in sun light either. I think I just didn’t have the patience and erasers were cheap and off the shelf in RadioShack. I continued to work with them for many years later in my job. (Broadcast Engineer) I came to the conclusion that the older the eprom was, or the longer it held its program the harder it was to erase! I can’t imagine erasing a 20 year old program. We stopped erasing them and would just buy new stock. Yes they were cheaper back then. (wasn’t everything!)

  28. A true hacker would have used a stack of static rams, an address decoder chip, and a battery to emulate the EPROM. Used to do that during development. A lot faster to write new code into the stack. Usually it didn’t have a battery since it was so fast to update.

    Ran into a problem with EEPROMs once because of using that RAM static. At startup we’d calculate the checksum of the chip memory and write it to the highest or lowest memory location, depending on where the processor started execution. Then compare the checksum and the value in that location. In an E(E)PROM the write failed so you were comparing with the original checksum. If the checksum was bad the system would reboot and try again.

    We got a bunch of EPROM that were based on an EEPROM design. Did the same checksum / write trick. The systems started having intermittent failures on the bench. Finally stuck a logic analyzer on them. Analyzers were way expensive at the time so had to rent one. Found that the EPROM was sending garbage onto the bus after the write for a few cycles corrupting the next instruction fetch. Off into the weeds!

  29. [quote] Or maybe fetch some old, and historically accurate, drum machine samples and burn them in to recreate a LinnDrum?[/quote]
    I think it would be a great project!
    Ps: when I watch this video (https://youtu.be/wdud_iisj1E) about the Linn I ask myself “why they haven’t conver the erasing windows?” okay, I don’t think you normally leave it open on the sun, but…

  30. I once was in a pinch and tried to erase 27c4096 EPROMs with a UV curing light used for hardening the UV polymerizing resin that is used as nail polish. That did not work out either. I left the parts in there for hours and not a single bit flipped.

    Regards,

    Jan

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