Those 'fake' UV EPROMs? - Page 1
Forum section: electronics / projects

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 10, 2025, 08:06:09 pm
content: I have a collection of these...I know a few years ago people thought maybe they were 'fake'... and others suggested they were re-badged 2732...I really need a 2732 right now...In my T56 Programmer I cannot program them as either 2732 or 2732A and I've tried a few voltages but mostly the programmer crashes and disconnects from USB is not well.It does manage to clear some bits though so they obviously do something... and UV erasing them does bring the FFs back.In 2025... is there any hope? (For my EPROMs at least!)PSI've never got a 1322 labelled one to work... I did have more luck with 0540 and 9348 labelled ones many moons ago.

author: wraper
author_rank: Unknown
timestamp: October 10, 2025, 08:39:59 pm
content: I wonder who thought it was a great idea to label them as manufactured in 2013. Like 10 years after they were discontinued.They probably need 25V programming voltage.Programmer may be crashing because USB voltage drop due to high current consumption. For example my Wellon programmer asks connecting PSU when programming these, despite working for USB only otherwise. Did you connect PSU to it? Also you could try rear USB port if it's a desktop PC, different USB cable. EDIT: It happens due to high current but because EPROM gets overvolted.

author: wraper
author_rank: Unknown
timestamp: October 10, 2025, 08:47:02 pm
content: Actually on one of the chips marking was poorly erased and there is PGM=12.75V written on it despite 21V written elsewhere. As all chips look to have the same die, they should be 12.75V chips as well. Also die size is too small for 25V chips.

author: wraper
author_rank: Unknown
timestamp: October 10, 2025, 08:49:02 pm
content: This is NMC27C32B from National semiconductor.https://www.pilianidis.gr/images/sync_products/03-NMC27C32Q/NMC27C32BQ%20150.pdf

author: Dan N
author_rank: Contributor
timestamp: October 10, 2025, 10:35:17 pm
content: I still have 3 of these from a school project in the 80s, so the attached pic shows that era's tech.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 11, 2025, 07:26:12 am
content: I had not noticed the 12.75V marking... That is very interesting.I guess is it is possible that they may have been damaged by me applying 21V to them during my attempts if they were not already defectiveWhat is the difference between a 27C32 and a 2732A?Looks like VPP max is 13V on the datasheet above.So from the photos we can clearly see they are not original as we thought.

author: squadchannel
author_rank: Frequent Contributor
timestamp: October 11, 2025, 09:04:14 am
content: Did you try rubbing it with IPA or acetone?bought it from China on eBay.I figured a 27C256 would be common enough, so even a fake would be fine.Sure enough, it was fake. They sprayed brown paint over an M27C256 and then laser-marked "M27C256" on top of that.Why do this to an identical part? Probably to claim it's new.Quote from: NivagSwerdna on October 11, 2025, 07:26:12 amI think "C" stands for CMOS. I interpret it as meaning it's been low-voltage .

author: wraper
author_rank: Unknown
timestamp: October 11, 2025, 11:21:30 am
content: Quote from: squadchannel on October 11, 2025, 09:04:14 amThose National semi ICs were marked with paint, so it's already rubbed off. Your EPROMs on other hand were laser marked, so counterfeiters had no other choice than to paint them over.

author: wraper
author_rank: Unknown
timestamp: October 11, 2025, 11:56:22 am
content: Quote from: NivagSwerdna on October 11, 2025, 07:26:12 amYou should be more specific with that. Assuming same speed grade, in read mode NMC27C32Bhas 300 times lower standby current, 10 times lower active current. Output drive capability is the same. Programming is a little bit different. Beside different programming voltage, NMC27C32B requires Vcc raise to 6.25V during programming (NMC27C32 with no B does not need Vcc rise but needs 25V Vpp), 0.1ms program pulse width instead of 50ms. When programing 27xxx, you need to be specific. You cannot just select whatever 27xxx with right programming voltage and assume it will work fine.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 11, 2025, 12:18:10 pm
content: So going off the suggestion earlier and the 12.75V hint which backs it up...and...All the dies look the same so maybe there is hope for them all!

author: NivagSwerdna
author_rank: Super Contributor
timestamp: October 11, 2025, 12:33:02 pm
content: 6 out of the 6 I have to hand all program and verify as NMC27C32B!I'm glad I asked!Thanks