Mac IIsi a fire hazard??

[LC_575]

I just had an incredibly scary experience with my recently acquired Mac IIsi.

I had it set up with with an Extended Keyb II, no monitor, and no mouse. I wanted to boot it to hear whether it's HD was functional.

I hit the power key on the keyb, and then saw a large electrical flash - like a firecracker - eminate from the rear of the IIsi, around near the exhaust fan. I quickly turned off it's power strip and stood there for a minute in disbelief.

I removed it's cords and then noticed a heavy, gunpower-like spell coming from the rear of the system. I brought it downstairs and opened the case, but visually there were no scorch marks, detonated caps, or fried chips on the motherboard. even the rear exterior of the case appeared fine.

What happened?

 

[Osgeld]

something in the power supply?

sniff around

 

[Dennis Nedry]

Something clearly blew in the power supply. Take it out, open it up, and take a picture of the damage! Maybe it can be fixed easily, maybe not, who knows.

Doubtful that it could have ever started a fire.

 

[Scott Baret]

Don't try that PSU as-is again. I also don't think it would set the Mac ablaze, but safety always comes first, especially if you've got sparks flying everywhere. Definitely repair or replace, whichever you're more comfortable with. Also, make sure it's disconnected from the wall at all times until a remedy is found!

I agree, pics are a must.

 

[Bunsen]

onoz, teh magic smoke haz axcaped!

 

[LC_575]

I'm not totally sure if i'll rip apart the PSU for repairs, considering that my school has a whole 'nother IIsi which is slightly less hazardous. However, I am curious as to what caused this. I booted it several times earlier w/o such a severe event; perhaps it was a one-time thing, and by that I mean it's never going to boot again.

 

[Danamania]

Sometimes it can be the tiniest visible break in a component that releases a massive flash of light, sparks, a stench that fills the room and enough noise to skip a few heartbeats.

This was one of those - http://en.wikipedia.org/wiki/File:No_blue_smoke.jpg

I had similar happen inside a Quadra 840AV PSU - it was a voltage regulator IC, from memory. Also rather small damage for the noise, light & sound it made

Dana

 

[Gorgonops]

Almost any kind of component can go kerpow like that. (Last one that happened to me was a flat-pack IC on a fairly recent hard disk's circuit board... the odor was positively unreal.) It could of been a voltage regulator IC, transistor, capacitor... I've even seen vaporized resistors and diodes.

If you crack open the power supply it'll probably be obvious what detonated, and if you replace it it'll probably be fine. (Well, possibly not. Sometimes a part will release its magic smoke because something upstream from it got shorted or failed in a way that it's letting far too much current past, so a replacement part will also go *bang*. Thus requiring some more in-depth troubleshooting.)

I'd put a nickel on it being a capacitor, or a regulator that failed because of a *shorted* capacitor. Any Mac II-series box is 20 years old now. (give or take about three years.) Computer collectors who are serious about using their machines rather than just displaying them are going to have to start accepting the fact that some parts don't last forever, and the limiting factors are more strongly correlated with age rather than how much use the machine gets. I wouldn't bet on another IIsi being any less likely to go *BANG*.

 

[LC_575]

For the short term I'll exchange either the network card or PSU between my two IIsi's, once I have both of them. However, when I saw this flash, it was almost wholly outside of the case, as if the flare of whatever vaporized was channeled out by the exaust fan - the IIsi doesn't have any vent on it's rear that opens to the PSU.

What precautions should I take when inspecting the PSU? I don't need a capcitor to discharge into my arm.

 

[Osgeld]

I bet it was a cap too, regulators usually burn not explode (though you never know), as far as safety have it unplugged (done) for a while and it should even back out, if your paranoid you can use a (insulated handle) screwdriver to short capacitor leads together

 

[Charlieman]

Storage location is an important consideration. If your old Mac has been stuffed in a loft, garage or anywhere damp, treat it with respect. Bring it indoors, to a nice warm and arid environment, to allow it to dry out. For about a week.

All of my psu bangs with Macs have occurred when I failed to observe the above rules.

 

[LC_575]

I have discovered the cause of the magic smoke release. It explains quite a bit (including why the flash occurred outside the case) and it may surprise you.

No, it wasn't the PSU, it's perfectly fine:



Uploaded with ImageShack.us

It was the NuBus riser card:



Apparently, when this cap (or whatever it is) blew, it sent a massive amount of voltage up the network card ribbon cable (on left). Then this excess voltage found the path of least resistance, which I believe is the RJ-45 outlet. This would explain why I saw a flash outside of the case, not exactly at the psu.



I didn't see this until I was about to pack it up - I noticed a very small scorch mark right on the pcb itself, with an orange shard of capacitor nearby. The motherboard itself has no orange-colored capacitors, and the PSU has none that are that small. A little more searching and I discovered the rest of the carcass on the NuBus card.

 

[techknight]

Ah, another one of those FRIGGEN tantalum capacitors.

tantalums are notorious for that as they age. they will short and explode. ive seen plenty of leader test equipment do this very same thing.

once one of the tantalums go, the rest will follow eventually. every single capacitor needs replaced, including the tantalum.

if the cap was just on a power rail, its LEAST LIKELY it has done any damage outside of the capacitor itself.

 

[Dennis Nedry]

Best of all, it appears to be very easy to fix, and everything will probably be just fine.

 

[Unknown_K]

Tantalums will go boom eventually, they cannot stand much over voltage at all by design (which you get when regulators in the PS age). I have a Daystar 040 PDS accelerator card I recieved with a blown tantalum capacitor, works fine as is but I replaced it anyway.

http://picasaweb.google.com/teozenios/NubusCards#5067908435668848786

Bottom right, hard not to miss.

 

[techknight]

yup, but you missed the one on the bottom left though...

 

[LC_575]

I managed to test out the IIsi's hard drive by puting it into my LC and then booting via boot floppy.

I have never heard a hard drive frantically click so loud in my life. it currently sits on my desk, dissembled for the fun of it.

So far this IIsi has been nothing but a disappointment. Riser card exploded, hard drive is faulty, memory useless for the 575, and the power supply probably doesn't regulate the voltage very well.

And I already have an auto-inject SuperDrive! Well, at least the battery isn't dead.

 

[techknight]

you could always strip it down and sell the ROM simm to an SE/30 enthusiast.

 

[Dennis Nedry]

None of my 9 iisi's have ROM SIMMs, they all have onboard ROM. How common is it for them to have the SIMM?