Older computer memory trouble

I have a system that I think is a Celeron 700. It was a nicely functioning machine. It has two memory slots. Here’s where the story begins. The computer is just full of dust beyond belief so I blow and vacuum it out. Them, I take out the single stick of 128mb PC133 memory out of it (the other slot is empty) for use in another system. I then install a stick of 32mb PC66 memory into each of the two slots. I power on the system, I get no beep, no video, and a strong burning smell. I quickly disconnect the power and remove the RAM and see that one pin in one of the RAM slots is burned/melted and so is the corresponding pin on the stick of memory.

What did I do wrong? Are you not supposed to use PC66 memory in a PC133 system? Did the dust get in there and short something? Was there a jumper I should have moved but didn’t?

I’m afraid to put the original PC133 128mb stick back in there for fear of damaging it.

did the computer work before you swapped out the PC133? if you put the other dimm in, the one without the burned pin, does it work? Where did you acquire the older dimms? Usually its OK to use a slower speed and not have a problem with it, I have used numerous different sizes and brands and never had issues, other than possibly slightly slower access. Did you literally vacuum the insides? Did you use your household vacuum or a shop vac or a computer vacuum? This can often damage components beyond repair from static. It is possible that the PC66 was damaged in the first place or might have been loose.


The PC66 was tested and working from another system (Celeron 333). To clean the C700 system I sprayed canned air while holding the household vacuum with hose nearby (not touching anything) to collect the dust in the air. The PC66 was not in the system at the time of vacuuming. I have not tried putting the original pc133 128mb stick back in the system.

Some older systems use jumpers on the board, or BIOS settings, to set RAM speed instead of auto detecting it. If that’s the case and it was still set to PC133, Well I have a blob of plastic on display on my desk from the same situation…

Memory frequency wouldn’t cause a burnout like that. Worst that would happen if the clock speed was off is the computer wouldn’t post.

The most common cause of a burnout is an improper installation. If the stick isn’t inserted all the way into it’s slot, or if it’s put in backwards (which I’ve seen a few times… the 2 alignment pins were mashed straight down), it can easily burn up. Less common, but also possible, is voltage- most modern SDRAM is rated at 3.3 volts, but some older EDO/FP/PC66 modules were rated for 5 volts. If you put a 3.3v in a 5v socket, or vice-versa, that may burn too. Some older motherboards did have jumpers to configure voltages for the memory and CPU, so that may be worth a look. Unfortunately, not all memory is clearly labeled, and sometimes it’s difficult to tell what is what, so it’s a risk to start mixing and matching.

Not true. I’ve done it, like I said, I have the RAM stick on my desk in the computer lab at school, it’s charred on one chip, the board had the jumpers set to 133 and it was 100 I believe, it didn’t burn out right away, but after a few minutes.

Newer computers would fail a POST, but AT style stuff was stubbornly determined to run, even if it was blowing itself out in the process.

You’re describing something like a short or severe overheat on one of the chips (though 100 -> 133 shouldn’t do that, and SDRAM doesn’t normally overheat in a single chip only); he’s talking about the contacts themselves being damaged. This is usually due to a crooked DIMM, but it’s possible (though rather unlikely) that he somehow managed to jam it in backward.

Very, very few AT motherboards used DIMMs. He’s likely got an ATX board. And I think that the generalization is a little bit of a stretch…

As for the voltage, a 5 V EDO DIMM (usually from a Mac) will have a different notch pattern, that would render it impossible to insert into a PC motherboard properly, unless you’ve somehow got a board which was designed to support both voltages and pinouts (I’ve never heard of such a thing).

By the way, don’t put the good DIMM in the bad slot; in fact, don’t put anything in there.

If I remember my abortive A+ sttempt, if your mobo is running at a speed higher than the ram it wont’t work, but as for the burning, I have no idea. One important piece of information would be if this was the slot you used with th older stick that had issues or the previously unused one.

What you describe has nothing to do with memory speed or jumper settings. These are the classic symptoms of a short circuit from power to ground. It was hot enough to stink in probably three seconds, that’s a lot of energy.

Without having the mobo and memory in front of me, I can’t say exactly, but likely it’s the wrong kind of memory for the mobo. Check the spacing of the gold contacts - the pitch of the 66 is probably larger & further apart than the 133.

The damaged socket should not be used if possible. If you must use it, clean the metal contacts (a toothpick is a good tool), even if you need to cut away some of the burnt plastic. Yes, there’s a risk of damaging the 133 stick, but if you do, you learn two things: PC133 memory is fairly cheap, and the mobo is fried. Of course, all might return to normal, and so there you are.

Memory is supposed to not fit if it’s the wrong type, but that’s not always the case, especially between fairly distant generations of the same form factor, and also anything will fit if you push hard enough.

Spend an hour cleaning up the mobo on the bench, and see what happens. Good luck.


I didnt have time to read all the reposts to your problem but, it could be the fact that you vacumed out dust. NEVER VACUMM a computer. ALways use the air can…