M5L2764K Reading/Programming - Page 1
Forum section: electronics / general

author: NivagSwerdna
author_rank: Super Contributor
timestamp: June 11, 2018, 12:44:25 pm
content: I have just bought an old PCB (arcade game) that has a number (10) of M5L2764K UV EPROMs. I have a TL866CS cheapo programmer from EBAYThe M5L2764K doesn't appear to be in the list of EPROMsI did manage to get the EPROM to read by selecting another 2764 device and setting Check ID to false but get slightly spurious results.One EPROM reads slightly different data every time (between 0 and 3 bytes randomly differ out of 8K)Is this device readable/programmable by the TL866CS? Is there another programmer recommendation that won't break the bank?Thanks in advance

author: Ian.M
author_rank: Super Contributor
timestamp: June 11, 2018, 01:25:39 pm
content: All 2764 EPROMs should be read compatible as long as you respect their speed grade. Its likely that the EPROM that is giving variable results is suffering from bit rot - decay of the stored charge on the floating gates.You *may* be able to recover it by reading it multiple times varying the Vcc over a range of about +10% to -30%, or by reading it multiple times while illuminating the die with various levels of visible light (with no UV). Both techniques shift the relative threshold of the sense amplifiers.You may need more control of the read cycle than the TL866CS can give you - consider using an Arduino Mega and bit-banging the access cycle. That also lets you vary the supply voltage under software control - just drive the Adj pin of a LM317L from a well filtered PWM output, put 1K resistors in the data lines to limit the current when EPROM Vcc is above Arduino Vcc, and on the Arduino side drive the pins as fake open drain (output low for logic '0', input for '1') with 10K pullups to EPROM Vcc.

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 11, 2018, 01:37:28 pm
content: It may also just be a timing issue. Those old EEPROMs have rather "high" read access time. Unfortunately, I don't see any option in the TL866CS support software to modify timings, nor any way to add custom chip profiles. Have you tried with other 2764 chips in the list just to see if it makes a difference? You could also take a look at the A0 address line on a scope to figure out the TL866 read speed and see if it could be the cause.

author: tsman
author_rank: Frequent Contributor
timestamp: June 11, 2018, 01:41:42 pm
content: 9 of your ROMs sound like they're reading correctly so it is only that 1 last ROM that is causing problems. Before you spend too much time or money on this, have you checked that your ROM set hasn't already been dumped by somebody? You can compare what you've read and what is in the dumped ROM set to see if there are any changes in your version.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: June 11, 2018, 02:18:05 pm
content: Quote from: tsman on June 11, 2018, 01:41:42 pmActually I only have tested 3 out of the entire set. #2 and #3 read repeatably. #1 is suffering bit rot as described and across the small set of bytes that read inconsistently it's unfortunately not revealing a particular statistical trend.Interestingly my set doesn't seem to completely match known sets but my board is a bootleg not original so possibly not a well known variant. I should really dump all 10 ROMs to get a better idea but they are quite rusted in so it's not a trivial undertaking.