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Old 09-20-2019, 07:39 PM   #1
BigTroll
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Default 286 ram woes

Got a 286 that keeps locking up after about 5 mins, I was told to try CheckIT and it found some bad ram, it also said it was in bank0. what would be the best way to go about finding the exact ram chip that is bad or should I just shotgun it and replace all of bank zero. the computer uses dipp ram 41256 chips.

Most of the chips are hyundai but some are oki. I noticed ebay prices for 41256 chips are ridiculous anyone have a sorce for real cheap dipps?
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Old 09-20-2019, 08:35 PM   #2
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Default Re: 286 ram woes

If you don't have a program that tells which bit is bad, you can simply swap chips from bank to bank and watch when the location changes, test again,... Should be able to pinpoint in 4 runs?

$1/piece isn't that expensive, is it?
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Old 09-20-2019, 08:38 PM   #3
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Default Re: 286 ram woes

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Originally Posted by BigTroll View Post
Got a 286 that keeps locking up after about 5 mins, I was told to try CheckIT and it found some bad ram, it also said it was in bank0. what would be the best way to go about finding the exact ram chip that is bad or should I just shotgun it and replace all of bank zero. the computer uses dipp ram 41256 chips.
Did you look at power AT THE CHIPS (under load)?
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Old 09-20-2019, 09:17 PM   #4
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Default Re: 286 ram woes

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Originally Posted by eccerr0r View Post
If you don't have a program that tells which bit is bad, you can simply swap chips from bank to bank and watch when the location changes, test again,... Should be able to pinpoint in 4 runs?

$1/piece isn't that expensive, is it?
it said bit 15 is bad according to the program how would I be able to find it on board? the $1 isn't too bad but I figure if I have the replace the whole bank which is 18 chips plus shipping it could get expensive, best deal I found was 25 chips for $13 plus 4 for shipping so I might just do that since it is the same 100NS ram.

I included a pic of the ram on the board, I also removed each chip, sprayed the sockets with QD electrical contact cleaner and reseated the chips.
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Old 09-20-2019, 09:18 PM   #5
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Default Re: 286 ram woes

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Originally Posted by Curious.George View Post
Did you look at power AT THE CHIPS (under load)?
Sorry to sound like a noob but I don't know what Iam doing, would I take a multimeter to a certain part of the board? I know the power supply in the unit was surprisingly a Seasonic SS200E I think warranty expired in 1991 according to the sticker
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Old 09-21-2019, 05:54 AM   #6
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Default Re: 286 ram woes

touch them, often bad dram gets very hot.
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Old 09-21-2019, 05:53 PM   #7
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Default Re: 286 ram woes

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Sorry to sound like a noob but I don't know what Iam doing, would I take a multimeter to a certain part of the board? I know the power supply in the unit was surprisingly a Seasonic SS200E I think warranty expired in 1991 according to the sticker
I always prefer using a 'scope to a DMM as it lets you see what's happening "in real time" instead of some "summary" measurement that hides those details. The loads that RAM presents to the power distribution system are synchronous wrt their access (all those nano-capacitors being charged/discharged as it performs its function).

If the RAM is "flaky", it could be attributable to crap on the power lines -- which could point to a flaky power supply, bad decoupling, etc. I.e., replacing the RAM device(s) could leave you with exactly the same symptoms.

OTOH, if the RAM is "dead", then clearly it needs to be replaced. However, even in that case, you'd want to have a look at the power rails to make sure there isn't a problem there that will take out your replacement part(s).
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Old 09-22-2019, 11:22 AM   #8
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Default Re: 286 ram woes

will this ram work? https://www.ebay.com/itm/Lot-of-25-N...0/392369732577 only problem i see is the datasheet for the NEC ram says its NMOS and the hyundai chips on the board are CMOS
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Old 09-22-2019, 05:32 PM   #9
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Default Re: 286 ram woes

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it said bit 15 is bad according to the program how would I be able to find it on board?

I included a pic of the ram on the board, I also removed each chip, sprayed the sockets with QD electrical contact cleaner and reseated the chips.
Pull *a* chip and run the test. See which "bit" has failed. It's possible that the chip you have pulled will be in a "bank" that isn't tested before the existing failed chip. In which case, the error won't change. Reseat the chip and make a guess as to which direction (on the board) will bring you to a bank that is tested earlier than you're current faillure.

Once you have pulled a chip that throws an error BEFORE your previous one, make a guess as to how the chips are arranged on the board to figure out where "15" likely lies.

Eventually, you should be able to identify the chips that handle bit 15 and then THE chip that handles the failure. You can then swap it with another chip to verify that the failure moves.

(It is helpful to be able to label the chips so you can remember where they came from else you're likely to lose track)
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Old 09-22-2019, 08:59 PM   #10
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Default Re: 286 ram woes

Quote:
Originally Posted by BigTroll View Post
will this ram work? https://www.ebay.com/itm/Lot-of-25-N...0/392369732577 only problem i see is the datasheet for the NEC ram says its NMOS and the hyundai chips on the board are CMOS
I use a older video card to test my dips, much more reliable.
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Old 10-02-2019, 09:40 PM   #11
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Default Re: 286 ram woes

Thanks for the help guys, I decided to get that lot of 25 ram chips/ebay deal, the good news is the computer is running great replacing all ram in Bank 0 with the NEC chips, the bad news is since the NEC ram is NMOS and not CMOS it runs about 20 degrees hotter then the cmos chips, Max temp I measured was 51c, where the max I think I got from the CMOS chips were 34c. Oh well she runs!
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Old 10-03-2019, 04:56 AM   #12
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Default Re: 286 ram woes

temp is not important, but they use more power.
not important here, but in a portable device it could be.
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