TL866 and ST-branded M27C256B UV EPROMs - Page 1
Forum section: electronics / general

author: Frotz
author_rank: Newbie
timestamp: February 13, 2018, 03:24:43 pm
content: I have 15 ST-branded M27C256B UV-erasable EPROMs and a Minipro TL866 chip programmer. The chips came as used off Ebay. When I try to program these chips, I get this:Code:$ minipro -p "M27C256B @DIP28" -w cleurom2.bin -SFound Minipro TL866A v03.2.80Chip ID OK: 0x208dWriting Code... OKReading Code... OKVerification failed at 0x200: 0xc8 != 0x00I thought that this was due to this particular variation of the 27c256 requiring more current than the Minipro burner could provide. So I bought a cable that has two male USB type A plugs on one end and a female type A jack on the other end. I've used variants of this for older hard drive enclosures that needed the extra current. This didn't help in the slightest. All of them fail programming in exactly the same way. Erasure goes fine. I've programmed several 27c256 chips from Texas Instruments with no problems. What's going on here? Am I better off simply trashing these chips?

author: wraper
author_rank: Unknown
timestamp: February 13, 2018, 03:41:59 pm
content: Post a photo of them including the die. They could be relabeled older EPROMs which I experienced when buying on ebay.

author: Frotz
author_rank: Newbie
timestamp: February 13, 2018, 05:02:26 pm
content: How would relabeled chips be able to return the correct chip ID?

author: wraper
author_rank: Unknown
timestamp: February 13, 2018, 05:17:10 pm
content: QuoteYeah, that would be strange but Chinese do make miracles happenThese chips certainly do not look like more recent revision as on the picture. I see chips from 89 and 92 with apparently different die. Do both of them fail programming the same? If you read it back, does it just program with errors or part of the EPROM remains unprorgammed? Have you tried programming single IC multiple times (set to not do blank check)?

author: wraper
author_rank: Unknown
timestamp: February 13, 2018, 05:25:26 pm
content: BTW, you could try programming them as TMS27C256 which have a tad higher programming voltage.

author: wraper
author_rank: Unknown
timestamp: February 13, 2018, 05:28:58 pm
content: Thinking again about it. Does programmer do blank check in the first place? Maybe the chips are not erased or erased incompletely. Try reading some fresh EPROM and look if it's completely blank to begin with.QuoteDo you mean erasure with UV? Just to be sure.

author: Frotz
author_rank: Newbie
timestamp: February 14, 2018, 02:53:06 am
content: Quote from: wraper on February 13, 2018, 05:17:10 pmThat difference in die size is due to reflections during photography. All the dies look exactly the same. Some parts are shinier than others at different angles. All of them fail like this: 0x200 to 0x27F are corrupted. The first byte is 0x00. Subsequent bytes are 0xFF. Bytes past 0x27F match what I want to put on the chip.Programming multiple times without an intervening erasure doesn't help.Programming as a TMS27C256 doesn't help.Each and every one of these chips fails in the exact same way.About erasure, yes, I mean with UV. I lit them up for 30 minutes and verified that they were blank prior to programming except for your suggestion that I program multiple times.

author: amyk
author_rank: Super Contributor
timestamp: February 14, 2018, 02:57:58 am
content: Check the pins of your programmer, make sure there's no unusual schmoo in the socket that could be causing partial shorts or flaky connections.

author: Frotz
author_rank: Newbie
timestamp: February 14, 2018, 03:30:05 am
content: Quote from: amyk on February 14, 2018, 02:57:58 amI ruled that out too.

author: Frotz
author_rank: Newbie
timestamp: March 07, 2018, 09:13:41 am
content: Would anyone like one of these questionable EPROMs to try with a known good (1980s or 1990s vintage) burner? I'd like to get to the bottom of the problem and hopefully rule out any problems in the tl866 or the controlling software (https://github.com/vdudouyt/minipro) for which I now have write access. I suspect a firmware or software problem because I confirmed some weird behavior for reading and writing GALs, which I'll talk about in another post.

author: wraper
author_rank: Unknown
timestamp: March 07, 2018, 09:48:52 am
content: Quote from: Frotz on March 07, 2018, 09:13:41 amWhy vintage, there are a lot of modern programmers which write them just fine. Not to say many programmers from 80's likely won't support them. I have Wellon WP-490 which had no issues with them. Although I doubt you'd want to pay for shipping to Latvia. I think you could check Vcc and Vpp while programming, they should be 6.25V and 12.75V respectively.

author: james_s
author_rank: Super Contributor
timestamp: March 11, 2018, 03:34:55 am
content: I have a GQ-4X programmer I could try on one if you like, it's not a vintage unit but it has programmed everything I've tried in it just fine. 0x200 is 1000000000 in binary which makes me wonder if these chips are half the size they claim to be. Have you tried programming one as a 27C128?

author: Mp3
author_rank: Frequent Contributor
timestamp: June 14, 2018, 12:40:58 am
content: Hi, has anyone solved this? Or is the solution to put a wire between the different pins?I can program new chips from Mouser or Digikey with no problem, and i double checked that every pinout is exactly the same, so i don't think i need to do the wire trick...I am having this same problem with a tl866cs and some AMD & TI branded 27c040. However, they might not be fully erased either.