Hi,
I have some DIMM's here and some of the chips on them look slightly different to the others, kind of dull on part of the surface.
Basically, I just wanted to know if it is possible to tell if the chips are blown by looking at them?
Thanks, Luke.
Depends on how long the short circuit current flowed for and how hot the IC became if it went with a big short. Other faults will not show at all for a visual inspection.
Although "eyeballing a fault" is a common practice and solves many problems with electronics, it does have it's limitations and more test techniques are needed to further isolate the problem.
Hope this helps, Peter
Unless it's *SEVERELY* blown (tops blasted off chips, cracked chips, scorched, charred, that sort of thing) probably not.
-- Don Bruder - dakidd@sonic.net
Differences in surface finish could be entirely due to moulding machine die/plastic variations. Not a reliable indicator.
OTOH, if you actually observe the smoke escaping...! :-)
Well, I don't know really...I'm trying to go through a load of RAM on a bunch of machines (which haven't been too reliable so far - well one has) and one one DIMM two of the chips have a dull surface rather than shiny (so you can see the text in the light).
I think that these are knackered, but again I need to test them some more to make sure.
Thanks all, Luke.
Surface finish appearance is absolutely meaningless. The mold release compound may have "bubbled" some as the casting was made, there may have been dust in the mold, variations in the formula, pigment, or even temperature of the plastic used for the case, how quickly/slowly the chips were cooled after the molding process, or any of about 14 bajillion other things may be responsible for mind-bogglingly huge visible finish variations, with none of them having any impact whatsoever on the functionality (or lack thereof) of the chip. Short of chips being blasted open, cracked, or charred (and even *THOSE* aren't
100% reliable, although they are a good indicator that the chip is probably hosed) there simply is no reliable visual indicator of a chip's functionality.Electrical testing is the only way to be certain. Visual inspection of the (electrically inert) plastic or ceramic shell of a chip CANNOT be relied on as a diagnostic of the health of whatever circuit is on the actual (electrically active) silicon wafer inside the chip. As an indicator that the chip *MIGHT* be gone? Perhaps it can offer a clue. As a definitive, or even slightly clueful, diagnostic? No possible way unless you're looking at a chip that's literally blasted apart, and even then, you can't be certain until proper electrical testing of the circuit on the wafer is performed. Anything else is purest voodoo.
-- Don Bruder - dakidd@sonic.net
I once found a faulty RAM in an Atari 520ST by touch. The particular IC was quite noticeably hot, compared to the rest of the RAM, so it seemed fairly likely to be the problem. I can't remember if there was some reason I suspected the RAM in the first place, though I must admit it was easier to find replacement RAM than some of the dedicated ICs, so perhaps I paid attention to RAM because it was something I could repalce.
I don't know about the state of DIMM manufacturing, but in 1996 I bought some 1meg 30pin SIMMs, and had a problem with one or more of them. It looked like some of the pins hadn't been soldered properly so I used my heat gun to reflow the solder. They worked fine for years after that.
It's odd how I paid $40 for those four SIMMs (and felt I'd got a deal considering I paid $80 for 64K of RAM in 1984), and just two weeks ago I paid $40 for a 128meg DIMM (and if the rebate comes in, it will be only $20).
Michael
On Wed, 17 Sep 2003 09:24:53 +0100, "Luke A. Guest" Gave us:
Some run hot, some do not. Blowouts are not usually visible as the power levels inside these sticks is not all that great.
Best bet is to take them to a PC store. Most of them have Memory stick testers. Or call around till you find one that does. They'll surely test them for free in the hopes of making a sale.
Yes, It's never a good idea to let the smoke escape.
Of course, at work we detect bad RAM cells by eye. But it frequently takes $50M worth of test equipment, and electron microscopes to make images that we can detect by eye. :-)
On Thu, 18 Sep 2003 11:41:04 GMT, "CWatters" Gave us:
It's not safe to watch ever either. Unless you are behind a slab of Lexan.
Not really. There are some exceptional cases where a defect makes a chip blow up and look accordingly. Some older chips did sometimes overheat which is also a means of testing, but nowadays you won't see anything on a electrically damaged or defective chip. Try programmatically testing them, there are some memory-testing programs available. Make sure however, that the CPU and chipset used for testing the RAM is reliable.
Yup. The old Finger Test can sometimes find a catastrophic failure.
NOTE1: Lick your finger first and get off the chip quickly. If you don't have the manufacturer's logo branded into your fingertip, you can go back for a longer, more definitive test.
The voice of experience on burned fingertips here.
Note2: This only finds really bad ones--it can't guarantee any are good.
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