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BigDumbDinosaur
PostPosted: Fri Aug 21, 2020 6:04 am 
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Dr Jefyll wrote:
The zoogies could also arise due to poor power/ground distribution....

Yep, which has the side-effect of interfering with good bypassing. Even at 1 MHz, dubious construction methods can give you grief.

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bgulotta
PostPosted: Tue Sep 08, 2020 9:35 pm 
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Just wanted to give an update regarding my issues. It turns out my suspicions where indeed correct. They were all due to a faulty RAM IC. Something about the one I originally received just didn't function properly except at very very low clock speeds. I ordered 2 replacements and both functioned just as expected. Thanks everyone for your help debugging.
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Dr Jefyll
PostPosted: Wed Sep 09, 2020 2:03 am 
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Glad you're having some success now. One question, if I may. After successfully testing the new RAM's, did you then also re-test the original RAM to verify that the malfunction returns as expected?

Worth a try, if you haven't done it already. That's because once in a while you may encounter a case where the chip is actually OK but nearby wiring on the board is flaky. Maybe there's a bad solder joint or a tarnished IC socket or whatever -- stuff happens, as they say! :roll: Replacing the chip can disturb the flaky wiring and make the symptom disappear -- and of course that makes the wiring issue superficially appear to be a chip issue.

-- Jeff

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BigDumbDinosaur
PostPosted: Wed Sep 09, 2020 3:52 am 
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bgulotta wrote:
Just wanted to give an update regarding my issues. It turns out my suspicions where indeed correct. They were all due to a faulty RAM IC. Something about the one I originally received just didn't function properly except at very very low clock speeds. I ordered 2 replacements and both functioned just as expected. Thanks everyone for your help debugging.

From where are you obtaining your parts?

Just for grins, you should try what Jeff suggested to see if it really was a foobar part.

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bgulotta
PostPosted: Wed Sep 09, 2020 4:46 am 
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Dr Jefyll wrote:
Glad you're having some success now. One question, if I may. After successfully testing the new RAM's, did you then also re-test the original RAM to verify that the malfunction returns as expected?

Worth a try, if you haven't done it already. That's because once in a while you may encounter a case where the chip is actually OK but nearby wiring on the board is flaky. Maybe there's a bad solder joint or a tarnished IC socket or whatever -- stuff happens, as they say! :roll: Replacing the chip can disturb the flaky wiring and make the symptom disappear -- and of course that makes the wiring issue superficially appear to be a chip issue.

-- Jeff


That is exactly what I did. I wanted to make sure I wasn't crazy. I guess moral of this story is to have extra ICs on hand.
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GARTHWILSON
PostPosted: Wed Sep 09, 2020 5:57 am 
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bgulotta wrote:
I guess moral of this story is to have extra ICs on hand

and be careful where you get them from, and use appropriate static protection handling. I have virtually no idea how many millions of ICs our company might have bought for the products I've designed them into, and to my knowledge, we have never gotten a bad one from a legitimate distributor. eBay is probably not the right avenue to buy through. Get them from the major distributors like Mouser and Digi-Key. There are hundreds more American distributors (and we do use other ones besides these two as well), but Mouser and Digi-Key work well even for hobbyists, and have an unimaginable inventory.

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BigDumbDinosaur
PostPosted: Wed Sep 09, 2020 8:57 pm 
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bgulotta wrote:
That is exactly what I did. I wanted to make sure I wasn't crazy. I guess moral of this story is to have extra ICs on hand.

I have to tell you I've been working with digital electronics for some 50 years and can count on one hand the number of defective parts I have gotten. New faulty chips these days are rarer than unicorns wandering the streets. On the other hand, purchasing parts from dubious sources can get you counterfeits...caveat emptor!

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