(How) Can I rescue these EPROMs? - Page 1
Forum section: electronics / projects

author: TomS_
author_rank: Frequent Contributor
timestamp: June 30, 2018, 03:17:25 pm
content: Ive got a bunch of old school UV erasable EPROMs that Ive held on to since I was a youngster and used to pull loads of things apart. IIRC some of these came out of a monster dot matrix printer that I picked up along with a really old computer, which now that I think back was probably a 68000 (I recall there being one very large chip in the middle). Sadly I didnt appreciate what I was tearing apart back then.Sadly though, as you can see, the leads of some of them look a bit worse for wear.Does anyone know what I can do to rescue these and bring them back to a better finish? Most of the bad ones seem to be branded AMD, I have a couple of others from other mfgrs like Intel which look like theyve come straight from the factory (early-mid 80's date codes).On one of them I tried the highest temperature on my iron (450C ish) and lots of fresh solder and flux, but that didnt really seem to do much.edit: EPROM, not EEPROM

author: stj
author_rank: Super Contributor
timestamp: June 30, 2018, 03:54:36 pm
content: a mini-tool / dremel with a steel wire-wheel will clean those up.dont use a brass wheel, it leaves a metalic layer on the ceramic.

author: ignator
author_rank: Regular Contributor
timestamp: June 30, 2018, 04:01:00 pm
content: For the IC ceramic body simple soap and water with tooth brush scrub.For the tin-lead plated leads, I would use a flux used by plumbers for cleaning copper pipe. Here in the states Oatey® #11 Liquid Flux. It is caustic. I've used it to clean soldering iron tips, and copper wires that I am tinning. You can use it for PCB work, but it must be fully cleaned or it will corrode the things it's left on.MSDS:Ammonium chlorideHydrochloric acid Zinc chloride

author: David Hess
author_rank: Super Contributor
timestamp: June 30, 2018, 04:16:28 pm
content: If the parts were originally soldered into place, I usually wipe the leads down with solder wick dipped in rosin flux using my soldering iron set to a lower temperature. I use thick stainless tweezers to straighten leads if necessary.If I was doing a lot of parts, then I would use a solder pot to tin the leads again and flick or wipe off excess.I like the idea of using a stainless wire wheel though; I will have to try that.

author: glarsson
author_rank: Frequent Contributor
timestamp: June 30, 2018, 04:46:42 pm
content: EPROM, not EEPROM.You don't need a window on an EEPROM as they are not erased using UV light.

author: james_s
author_rank: Super Contributor
timestamp: June 30, 2018, 05:40:52 pm
content: You might try using a pencil eraser. It works well to support the leads on the edge of a piece of plywood or other stiff material and then gently scrub along the direction of the pins a bit like combing hair. Metal polish may work well too, I have some stuff called "Mothers" that is intended for polishing kitchen pans and such which I use on all manner of other things. There must be something similar in your part of the world.

author: TomS_
author_rank: Frequent Contributor
timestamp: June 30, 2018, 05:44:16 pm
content: Quote from: glarsson on June 30, 2018, 04:46:42 pmYes, sorry. So used to writing EEPROM in these times.

author: TomS_
author_rank: Frequent Contributor
timestamp: June 30, 2018, 06:03:05 pm
content: Quote from: David Hess on June 30, 2018, 04:16:28 pmI dont believe they were, certainly I didnt have the tools to desolder parts like this way back when.I guess it was just poor quality tinning.Steel wire brush does sound like it could work, I need to get myself a dremel (its been on my shopping list for a while!)

author: C
author_rank: Super Contributor
timestamp: July 01, 2018, 12:14:22 am
content: Not much point in saving them unless you what something to show or have something built to use them.For a new project would be much easer and cheaper to use a new eeprom or flash memory chip. This would also allow what is attached to update the contents of the chip.A large number of these old chips can be replaced with just one chip.Think if you check prices you can get a 512k 32-pin dip for less then $5.00. And you do not have to use the full space, just strap un-needed address pins to a level..For a 68000, you just want to have two byte wide chips that are accessed in parallel. You have the odd/even address Roms.C

author: innkeeper
author_rank: Unknown
timestamp: July 01, 2018, 03:20:32 am
content: those so look like tarnished silver..i wonder if the aluminum and baking soda trick would work

author: scuzzyTerminator
author_rank: Regular Contributor
timestamp: July 01, 2018, 05:56:38 am
content: Well, these look in really great shape to me. They were certainly not used for firmware development.

author: TomS_
author_rank: Frequent Contributor
timestamp: July 02, 2018, 06:29:30 pm
content: Quote from: scuzzyTerminator on July 01, 2018, 05:56:38 amThey certainly havent been by myself, and all were pulled from production items. Theyve had a very sedintary lifestyle since - I did manage to read the contents off them all - whether it is valid I'll never know, but there are strings of text that I can read just fine in there.Some of them I had left in the sun thinking they might be erased, but still have contents today!

author: james_s
author_rank: Super Contributor
timestamp: July 02, 2018, 09:51:43 pm
content: It actually takes quite strong UV to erase an EPROM, I forget the calculations I saw but it was something like months of strong direct sunlight to fully erase, window glass absorbs much of the UV too hence the windows in the EPROMs being made of quartz.The main reason for the protective stickers over the window is that it takes much less light striking the chip to temporarily disrupt things. That is actually an interesting experiment, program the EPROM and install it in something and then shine a flashlight on the thing and it will malfunction.

author: Cyberdragon
author_rank: Super Contributor
timestamp: July 02, 2018, 10:10:42 pm
content: Reminds me of the movie Real Genius when they replaced the PROM in the laser weapon with an EPROM but left the PROM on the floor. The evil professor looked all over the board for an empty socket, ignoring the totally out of place EPROM, and the fact that they left the panel open. Come on now...

author: james_s
author_rank: Super Contributor
timestamp: July 02, 2018, 10:12:40 pm
content: I saw that movie again fairly recently, it had some moments like that but overall the tech stuff is fairly realistic by Hollywood standards.

author: David Hess
author_rank: Super Contributor
timestamp: July 04, 2018, 01:05:37 am
content: Quote from: james_s on July 02, 2018, 09:51:43 pmOxygen in the air absorbs the needed short UV also. Longer wavelength UV lamps are not sufficient; it takes the shorter wavelength UV lamps. You can smell the ozone produced when using an UV EPROM eraser. The lamps need a quartz envelope also.X-rays work for erasing any floating gate memory unless it is packaged inside of an x-ray absorber.QuoteThat makes more sense than protection against erasure. I will have to test that.Quote from: james_s on July 02, 2018, 10:12:40 pmIt was unusually realistic by Hollywood standards. The laser would have just burnt a hole right through the popcorn instead of popping it though.

author: innkeeper
author_rank: Unknown
timestamp: July 04, 2018, 02:25:29 am
content: lol, I ran across my heathkit EPROM eraser the other day...totally forgot i and that thing.

author: stj
author_rank: Super Contributor
timestamp: July 04, 2018, 10:15:31 am
content: i knew a guy in the southern u.s. who erased eproms by putting them in the hood of his car for a day.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: July 04, 2018, 10:50:35 am
content: Whilst we are on the subject of EPROMs..... I have some old EPROMs where some of the bytes are not reading their original values...Should I erase them and reprogram them? Do they need to 'refreshed' every now and again? (They are 1980s vintage)*Assuming that internally they use some sort of charge to store data and over VERY long periods of time that ebbs away?

author: David Hess
author_rank: Super Contributor
timestamp: July 04, 2018, 03:20:30 pm
content: Quote from: NivagSwerdna on July 04, 2018, 10:50:35 amThey should not need refreshing unless they have been mistreated or were programmed incorrectly. Production programmers are suppose to verify under worst case conditions which means fiddling with the supply voltage and do other things for long term reliability but often development programmers were used in production.QuoteThat is sort of how it works but the charge is trapped in a thin gate oxide layer via quantum mechanical effects. So it does not "leak" past an insulator in the traditional sense.

author: helius
author_rank: Super Contributor
timestamp: July 04, 2018, 03:54:32 pm
content: The charge tunnels out the same way it tunneled in. Memory retention in floating gate devices like EPROMs and Flash is from 10 to 20 years depending on temperature.

author: David Hess
author_rank: Super Contributor
timestamp: July 04, 2018, 04:10:45 pm
content: Quote from: helius on July 04, 2018, 03:54:32 pmIt is a minimum of 10 to 20 years under worst case conditions although some parts are rated at 100 years or more. In practice, the failed EPROMs I have seen were either defective or programmed poorly like with a development programmer. Some mask ROMs (Damn you Mostek!) have a lower reliability than good EPROMs.Bleeding edge NAND Flash is another matter; some if it suffers data loss after only months.

author: stj
author_rank: Super Contributor
timestamp: July 04, 2018, 04:19:32 pm
content: Quote from: helius on July 04, 2018, 03:54:32 pmon paper anyway.in reality eproms hold for 25years+ and flash may last 10years.i have a theory on this, it could be slow leakage through the gate used to erase the cell that reduces the life of flash-data.eproms dont have that gate.

author: james_s
author_rank: Super Contributor
timestamp: July 04, 2018, 05:41:28 pm
content: I fixed a mid-80s dumb terminal a couple years ago by reading one of the EPROMs and re-programming it with the same data. It worked fine when I got it, then started kicking out a ROM error occasionally, then more frequently then all the time. It read fine in my programmer but running at full speed in the terminal it couldn't quite cut it.I also worked on an arcade board a while back where I programmed a set of sprite ROMs and it would work fine then the sprites would start to show progressively more random noise within about an hour. Turned out the EPROMs I used were too slow and they would degrade enough in the hour or so after programming to cause problems.

author: Jester
author_rank: Frequent Contributor
timestamp: July 04, 2018, 08:32:38 pm
content: White pencil eraser works wonders on corroded pins like that.Back in the day (70's) I fixed color TV's. Very common problem on the Zenith models with 16 pin DIP TI chips used on the color boards was wonky color. Pull the IC, insert a pencil to support the pins, a few passes with my Staedtler white eraser, re-isnstall the IC's and good as new. Easy money at the time.

author: stj
author_rank: Super Contributor
timestamp: July 04, 2018, 09:11:04 pm
content: yes, but in the last century pencil erasers where fine sand bonded together with rubber.now erasers are plastic.

author: David Hess
author_rank: Super Contributor
timestamp: July 05, 2018, 05:02:16 am
content: Quote from: stj on July 04, 2018, 04:19:32 pmFlash has two problems:NAND Flash wires the cells in series but this allows read and write disturb so accessing the device damages unaccessed data. NOR Flash and EEPROM used for embedded memory do not have this problem.NAND Flash was scaled aggressively for higher density so loss of charge from the tiny floating gate is a serious matter. 3D NAND rectifies this by using much larger cells but stacking them vertically to make up for the loss of density. Embedded NOR Flash and EEPROM are built on much less dense process and this limits what process microcontrollers and other devices which use embedded memory are built on.

author: Cyberdragon
author_rank: Super Contributor
timestamp: July 07, 2018, 07:16:27 am
content: QuoteWouldn't electronics get destroyed at security checkpoints then?

author: RoGeorge
author_rank: Super Contributor
timestamp: July 07, 2018, 07:21:48 am
content: It should be very easy to clean the oxide with a pencil eraser:https://hackaday.io/project/7574-the-devil-is-in-the-details/log/26489-a-pencil-eraser-trick

author: David Hess
author_rank: Super Contributor
timestamp: July 07, 2018, 10:39:34 am
content: Quote from: Cyberdragon on July 07, 2018, 07:16:27 amIf you left the floating gate memory inside the x-ray machine, sure. Otherwise the exposure is too brief.

author: james_s
author_rank: Super Contributor
timestamp: July 07, 2018, 05:12:07 pm
content: I recall someone trying to use xrays to erase some OTP EPROMs, it did work to erase them but it also damaged them and they could not be reliably programmed afterward. It's something I've been tempted to try, but haven't got around to it.