W27C512 EEPROM Frustrations - Page 1
Forum section: electronics / beginners

author: CRCLARKE
author_rank: Contributor
timestamp: January 05, 2020, 06:31:16 am
content: I am relatively new to eeprom programming, but i am gaining plenty of experience.... I have been working with the w27c512 and I am having some real struggles with erasing the eeprom. I have built an Arduino breadboard programmer based on Ben Eaters, along with an erasing module, wired it properly and followed the voltage requirements. I tested it and it works well.The problem is, out of 10 chips, only 3 work properly, 3 won't erase, and 4 went up in smoke during erasing. I am not sure whats wrong, are they defective chips? am I not erasing properly? I do not use the verify algorithm, is it required? 3 erase just fine. I also don't use any timing to erase, just 2 push buttons. One for VPP and the other for CE...... I tried erasing at 12v and it works on the good chips, but had no effect otherwise.I am once again 1 short on chips and the project is shelved.I have just ordered a 20 pack of w27c512, luckily there pretty cheap but the wait sucks. I really hope I don't have this much trouble with the next batchHas anyone had this trouble before?Are there any tips or tricks to erasing these eeproms?Thanks!

author: Nerull
author_rank: Frequent Contributor
timestamp: January 05, 2020, 08:05:31 am
content: If you're burning chips than you likely do not have something wired correctly.

author: Ian.M
author_rank: Super Contributor
timestamp: January 05, 2020, 09:22:50 am
content: TheW27C512 datasheetsays it requires +14.0V +/-0.25V Vpe to erase on /OE and A9, will draw 30mA from Vpe and the abs. max. voltage those pins can tolerate is only +14.5V.That's not a lot of margin between a successful erase and blowing the chip, so your Vpe switching circuit must provide clean edges free from overshoot, ringing etc. Also the spec says the /CE pulse to trigger erase is 100ms +/- 5ms, so there's no way you'l meet those specs with a simple pushbutton.At the minimum you'll need a debounce circuit for the button, an active Vpe switching cicuit that can handle >30mA with negligable voltage drop, and some monostables to sequence Vpe and /CE with correct timing. Best bet would be to do the sequencing and timing with the Arduino.

author: CRCLARKE
author_rank: Contributor
timestamp: January 05, 2020, 05:25:11 pm
content: I am pretty sure it is wired correctly because I have erased several eeproms successfully, and the eeproms that do work I have erased several times successfully.I am operating within the voltage tolerances, and have even successfully erased at 12v. I am aware of the 100us CE pulse but it does not specifically state a maximum time for VPP or A9. No issues reprogramming the chips, but only the ones that survived erasing made it to reprogram. and they have repeatedly worked as I was expecting. but it is total hit and miss, mostly miss. I feel it has something to do with that A9 voltage. I wish I knew how it worked, I added a current limit resistor to A9, didn't help, though it made the failures less catastrophic.I can setup some timing for the erase, but I am skeptical about there being a difference....... and I don't think a denounce would help, because so what if it erases multiple times, but I can test it.3 of the chips work reliably with my setup.... so far anyway, maybe there just tough, but I would expect them all to be identicalI will have to wait till new chips arrive to test because the chips that work, always work and the chip that don't, don't respond to anything so I have no way to differentiate the testSo I got some time to brainstorm till the new ones show up, so lay it on me!

author: james_s
author_rank: Super Contributor
timestamp: January 05, 2020, 05:29:45 pm
content: Buy a TL866 and use that, they're only about 40 bucks and will easily save you money in the long run if you are blowing chips.Also where are you getting the EEPROMs? If they're from China they're likely pulls, many might not be EEPROMs at all. I once bought a couple of EEPROMs that turned out to be random 28 pin ICs that had been blacktopped and re-marked, I wiped them with acetone and the black paint came off the top.

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 05:44:16 pm
content: If you bought them from China probably you got mix of different ICs, most of them being OTP EPROM. It's quite often that old marking is removed and new marking is applied. I once ordered exactly the same UV EEPROMs from the same seller twice with one week difference. First batch was what it should be, second batch had much larger die. Turned out to be way older IC from different vendor and with 21V programming voltage instead of 12.5V. The thing was that despite differences in packaging, both had exactly the same marking with the same date code. Also happened with ATTINY24A which had the same marking on top but actually were mix of ATTINY24 and 24A. Also although they had the same lot/date code on top, on the bottom side it was different. While normally it should match. Turned out to be blacktopped and remarked. So even if marking does match, check if there are no differences in packages, if any marking on bottom side does match if they have the same date code on top. Also try rubbing them with acetone or some other organic solvent and see if marking comes off.

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 05:53:48 pm
content: They are poorly visible on photo but seems some have dimple on corner and some doesn't. Also here for example is an ebay listing with obviously remarked IC on the picture.https://www.ebay.com/itm/10PCS-EEPROM-IC-WINBOND-DIP-28-W27C512-45Z-W27C512-45/123882775460?hash=item1cd7fd23a4:g:~9QAAOSwLpRdXpAiOthers may look much more sophisticated buy still remarked.

author: CRCLARKE
author_rank: Contributor
timestamp: January 05, 2020, 05:59:19 pm
content: That's interesting because that is basically what happenedQuote from: wraper on January 05, 2020, 05:44:16 pmThat's interesting because that is basically what happened, I first ordered 5 from china (everything comes from china) and had 2 bad? chips, so i then ordered 5 more about 2 weeks later from the same seller, and I think only 1 actually worked, which brings us to now, but the numbers on the chips are etched in, so I don't think they are repainted or rebranded. So the new batch I ordered from another seller, but still from china.Does anyone know where to get eeproms NOT from china?

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 06:04:45 pm
content: Quote from: CRCLARKE on January 05, 2020, 05:59:19 pmThey are marked with laser, which I can do at home. Old marking it either scrubbed with very strong solvent if it was originally paint, or sanded and blacktopped if it was marking made by laser. Then new laser marking applied.

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 06:12:27 pm
content: Clueless naivety:

author: Bud
author_rank: Super Contributor
timestamp: January 05, 2020, 06:30:27 pm
content: There is your problem. Buy from a reputable source.

author: Ian.M
author_rank: Super Contributor
timestamp: January 05, 2020, 06:42:56 pm
content: Implement ID readout with A9 pulsed to 12V (see Table of Operating Modes' on page 7 and left side of 'Erase Waveform' diagram on page 13). That should be non-destructive on any JEDEC compatible EPROM or EEPROM >64K.Before attempting to program a 'new' chip, check the device ID. If you don't get the correct ID bytes, DA 08, its a remarked fake, not a genuine Winbond W27C512. If it lets the holy smoke out, then its probably not even a non-volatile memory chip! If it already has data in it, its recycled not new.

author: CRCLARKE
author_rank: Contributor
timestamp: January 05, 2020, 06:52:31 pm
content: Upon closer inspection of the chips, maybe? probably? the have been rebranded. There are some definite physical variations in the chips, but even the working ones have some variances.but knowing this information doesn't help a lot....so i guess the lesson is:Quote from: Bud on January 05, 2020, 06:30:27 pmbut none of shady sellers admit to being "non-reputable"Where do you get Your eeproms from?Quote from: Ian.M on January 05, 2020, 06:42:56 pmHey, that's a good idea!!!also, less than half of the chips were erased when i received them

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 06:57:24 pm
content: Clearly counterfeit. Packages are different but marking is exactly the same. Genuine components from different batches cannot have exactly the same lot, date code and other information (bottom row). Some ICs are obviously salvaged since there are soldering signs on their leads. Certainly try rubbing them with acetone, some look like they could be sanded and blacktopped.

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 07:12:39 pm
content: Quote from: CRCLARKE on January 05, 2020, 06:52:31 pmOn ebay there are basically none, especially in China. If you get genuine part one time, does not mean you get a good part next. Also most of counterfeits "work"*, so most hobbyist buyers don't even have any clue they were duped.*"work" does not mean they meet specifications or work properly in all applications they should. For example audio opamps like AD797 sell like hot cakes on ebay but barely any of them are genuine. But most buyers leave positive feedback. And even if you have genuine parts, it's really hard to compete against 50 sellers with counterfeit crap. Barely anyone wants to buy at genuine component price. And the worst part is that even if you buy at high price does not mean you'll get genuine part. Though chances are certainly much higher.

author: james_s
author_rank: Super Contributor
timestamp: January 05, 2020, 07:21:44 pm
content: If you get parts that are clearly counterfeit, submit an item not as described claim with ebay and get your money back. The counterfeit sellers proliferate because hardly anyone bothers to do this. Just be 100% sure so you don't falsely accuse an honest seller.With old parts like DIP EEPROMs it can be really hard to find a legit source for genuine parts. I have no problem paying for used pulls if they're sold as such. What bothers me are all the sellers passing them off as brand new.

author: CRCLARKE
author_rank: Contributor
timestamp: January 05, 2020, 08:32:40 pm
content: I watched the video (posted above) about counterfeit components........ and it raised 2 questions to me.....1. Why relabel something other than what it is? After all, it already has a label and proper function, it would seem easier to sell an orange as an orange rather than trying to paint it to look like an apple.2. Unless the they have a fully automated system, it seems impossible to profit from manual chip salvage in bulk. If it took only a minute to refurbish each component, then even at a $1 each per component, the labor required is BARELY worth the return.I can buy almost any new component or even IC's for a $1 or less.I am pretty sure a person could sell salvage components as is and with less effort , and make better money. why would anyone refurbish a capacitor? for money no less?

author: Bud
author_rank: Super Contributor
timestamp: January 05, 2020, 08:42:29 pm
content: Quote from: CRCLARKE on January 05, 2020, 06:52:31 pmI mean industrial parts suppliers, Digikey, Mouser, Arrow, Element14, and such. If you get your parts from random sellers on .bay and .express, you will always be in situations like the one you are in right now, that is - you will not know if the problem relates to bad parts or to your designs. You can eliminate the parts variable in the equation and focus on designs.

author: CRCLARKE
author_rank: Contributor
timestamp: January 05, 2020, 08:51:21 pm
content: DigiKey is my favorite site! They are not always the cheapest but they are reliable and best of all they have quick shipping. Especially for the average Canadian Eskimobut they do not offer a lot of options for eeproms.

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 09:03:05 pm
content: Quote from: CRCLARKE on January 05, 2020, 08:32:40 pmBecause you can sell counterfeit (functionally similar) or salvaged component as new and genuine. That's besides cases when internals do not match in function. Even in those cases you can "create" what's currently in demand.QuoteDone by cheap and fast labor. If you create $100 of components per hour with $10 labor, it's a quite decent profit. In cases when components are counterfeited from scratch, not salvaged from e-waste, process is mostly automated like in normal IC production. Don't forget that you can buy stuff from China for less than $1 including shipping. Compared to that process of counterfeiting is a gold mine.QuoteThere are tons of counterfeit components sold for <5 cents a piece.

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 09:05:12 pm
content: Quote from: CRCLARKE on January 05, 2020, 08:51:21 pmBecause you want to buy obsolete stuff no longer in production. Your best bet is compatible component from smaller manufacturer which produces alternatives for obsolete components.Quote from: CRCLARKE on January 05, 2020, 08:32:40 pmBecause nobody will buy used with few exceptions like producers of counterfeit power bricks. But don't expect they will pay the same price.

author: wraper
author_rank: Unknown
timestamp: January 05, 2020, 09:18:52 pm
content: Actually recently I found counterfeit (e-waste) 330uF 450V capacitors in power supplies used in elemental analyzers which cost around $30k. Made by German manufacturer (fuck you Eltrahttps://www.eltra.com/). Although those idiots outsourced PSU to some dodgy Chinese manufacturer.

author: CRCLARKE
author_rank: Contributor
timestamp: January 05, 2020, 10:11:11 pm
content: i can see the value in some components, but for the most part it seems like setting up to counterfeit money, but only producing dollar bills.....with a bit more effort you could counterfeit something worth the profit, or just make an authentic product......and i have no issues with used components, i use them often in repairs, but i know they are used and they work just fine... usually, but that is the risk of used.

author: amyk
author_rank: Super Contributor
timestamp: January 05, 2020, 10:45:08 pm
content: Besides the discussion about fake parts, I would also recommend investing in an oscilloscope. Even genuine parts are unlikely to tolerate timing and voltage outside of spec. "Externally timed" EEPROMs like these can be easily damaged if the erase/program pulses are too long.

author: james_s
author_rank: Super Contributor
timestamp: January 06, 2020, 01:46:44 am
content: Quote from: CRCLARKE on January 05, 2020, 10:11:11 pmIf you have 100,000 useless junk ICs like mask ROMs or some other worthless part and loose morals, you can run the lot through a machine that sands off the top and marks them with a new part number and now you've got something that was worth $0 that you can now sell for $1 or more each, that's $100k minus whatever you spent re-marking them which is often not much in volume. It can be very profitable, even for low value parts.Not all parts bought direct from China are suspect but certain types of parts nearly always are. Older parts that are no longer produced and still in high demand are most commonly counterfeit but you can find fake jellybean transistors if only because marking a big pile of reject transistors as 2N3904s and selling packs of 50 for a few dollars is more profitable than throwing them away.

author: edavid
author_rank: Super Contributor
timestamp: January 06, 2020, 04:50:54 am
content: It's a lot easier if you have either a known good programmer or known good ICsBut if you do want to build your own programmer, why not choose 5V only parts like the SST39SF010A? They are still very cheap.

author: CRCLARKE
author_rank: Contributor
timestamp: January 06, 2020, 06:17:49 am
content: Quote from: edavid on January 06, 2020, 04:50:54 amwell i am still pretty new to this and don't have a ton of experience with chip options. i checked out that chip you mentioned, what a great option!! i think i will pick some up, but my current project requires a 28 dip, can you recommend one to me? and maybe some other options?

author: mikerj
author_rank: Super Contributor
timestamp: January 06, 2020, 01:44:12 pm
content: Quote from: CRCLARKE on January 05, 2020, 08:32:40 pmBecause apples may be in higher demand and therefore worth more money than oranges.Quote from: CRCLARKE on January 05, 2020, 08:32:40 pmSo why not buy your 27C512 brand new for $1? You simply can't.

author: edavid
author_rank: Super Contributor
timestamp: January 06, 2020, 04:04:36 pm
content: Quote from: CRCLARKE on January 06, 2020, 06:17:49 amI don't know of a 512K bit, 28 pin, 5V only part, but you can consider:AT29C256 256K 28 pin 5VSST27SF512PG 512K 28 pin 5V/12V, but not quite as finicky as W27C512

author: wraper
author_rank: Unknown
timestamp: January 06, 2020, 04:12:46 pm
content: Quote from: edavid on January 06, 2020, 04:04:36 pmAnd have the same counterfeiting issues as both are obsolete as well.

author: edavid
author_rank: Super Contributor
timestamp: January 06, 2020, 05:53:55 pm
content: Quote from: wraper on January 06, 2020, 04:12:46 pmAt least they have signatures and are 100% testable. For a hobby or repair project, isn't that good enough?What would you suggest as an alternative if a DIP28 part is needed?

author: CRCLARKE
author_rank: Contributor
timestamp: January 06, 2020, 07:06:07 pm
content: Quote from: edavid on January 06, 2020, 04:04:36 pmThank-You edavid,I have added those to my list!Does anyone else know of some other good options for dip eeproms?

author: richnormand
author_rank: Unknown
timestamp: January 06, 2020, 07:24:45 pm
content: You might enjoy reading this primer:http://muanalysis.com/wp-content/uploads/2019/01/Counterfeit-or-retrofit.pdfNote for full disclosure: I know the author.

author: wraper
author_rank: Unknown
timestamp: January 06, 2020, 07:51:13 pm
content: Quote from: edavid on January 06, 2020, 05:53:55 pmBoth SST27SF512 and W27C512 have ID code, so moot point. What I know there is virtually no genuine SST27SF512 in DIP package on ebay. Actually you'll get re-marked W27C512 at best as supply of SST27SF512 is much scarcer and it's more expensive. Or more likely re-marked OTP EPROM.QuoteOTP AT27C512R from Microchip (Atmel) which is still in production if you can live without re-programming. Or something not in DIP.

author: edavid
author_rank: Super Contributor
timestamp: January 06, 2020, 08:03:37 pm
content: Quote from: wraper on January 06, 2020, 07:51:13 pmSo far I have had a 50% success rate buying SST27SF512s on AliExpress @ $0.60. I just got refunds on the bad ones and moved on. For hobby projects that's OK. Fortunately there are not many cases where you need DIP28 512K parts.It's easy to find real windowed 27C512s in the US, so I don't think I would bother buying OTPs. Flash is so much more convenient though.

author: CRCLARKE
author_rank: Contributor
timestamp: January 06, 2020, 08:41:22 pm
content: Quote from: edavid on January 06, 2020, 08:03:37 pmagreedIts much easier to deal with counterfeits when you know when and where they come up. At least you can hedge you bets and expect losses

author: hermitengineer
author_rank: Regular Contributor
timestamp: January 06, 2020, 11:52:26 pm
content: If you're okay with one-time programming, Microchip still makes a 27C512. Or, at least, Mouser still has them in stock. On the bright side, that saves you from building an eraser.https://www.mouser.com/Semiconductors/Memory-ICs/EPROM/_/N-488ye?Keyword=27c512&FS=True