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ROM Chips keep reading different values

tblake05

Experienced Member
Joined
Aug 21, 2017
Messages
295
Location
Minnesota
Hey guys, me again. Working on a 1979 fresh Atari Asteroids console. AR Board, PSU, and Monitor all rebuilt. Recapped the game board but it wont boot. Verifying the ROM chips in my mini pro shows at least one not close. Another two will read and are close but inconsistently read the same. As in I can read it, and immediately read it again and it will output totally different though close but different. The third chip consistently reads and verified perfect against the roms posted online.

What would make the chips not consistently have the same code? Half erased? They have stickers over the top of them to protect against light. And the stickers are dated 1979.

Coinsidently there are 4 ROM chips, the 3 not reading out right are AMD AM4716DC Chips dated 1979. The one which always reads correct is a TMS 2516JL.

Plus what chips can I use the are EEPROMS that my programmer can erase Rather than the type which requires light to erase.


Thanks for any info!
 
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An EPROM will not hold its data for ever is the simple answer. The charge (in the insulated gate) leaks away (depending upon whether you are an electron or a hole thinker that is)...

From what I remember, most manufacturers will only guarantee that an EPROM will hold its data for 10 years. Clearly they are on the pessimistic side - and a device will hold its data for much longer than that. However, how long is the question...

At a certain point in the life, the device will stop being a 'digital' device and will start behaving like an 'analogue' device - thus giving you a '1' or a '0' depending upon environmental conditions: voltage rail, temperature, the amount of electromagnetic interference, the amount of light falling on the device etc. etc. etc.

Usually, erasing and reprogramming the device cures all ills (assuming you have a file with the correct contents of the EPROM to burn it with of course).

TMS is Texas Instruments and AMD is obvious (AMD) so they are from different manufacturers.

Do you have the 'correct' contents somewhere to burn a new set of EPROMS from?

Dave
 
Hi Dave!

yes I do. The romset dumps for arcade games and pinball machines are open source posted on the internet.

The set I have, there’s 1 that verifys 100%, the other two match fairly close though not 100%, and the last not at all, and is only reading out in bits of 00,40, or 80. That’s it. So that one is definitely a problem.

maybe I’ll change out all 4. What chips should I order?
 
I have run into EPROMs where very dirty legs caused intermittent problems and I had to rock the chip in the socket after burnishing the pins before I could reliably read a chip in and then verify it back successfully. Likewise I have run into chips where the newer programmers couldn't supply the correct voltage and the weaker bits would drop out until I used a much beefier programmer like my Data I/O 29B.

What chips should I order?
Well if it wasn't already obvious, any 4716 EPROM will work.
 
Is Atmel ok brand? 28c16 specifically? I can get a bunch of them (from china) and they aren't super expensive. Or should I stick with the old UV erasable 2716's?
 
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