Date   : Mon, 22 Jan 2007 14:51:03 -0000
From   : dm.hunt@... (David Hunt)
Subject: Narrow Escape...

> Yes, only 3 weeks in and already we have the first BeebMaster 
> explosion/fire/disaster of the year!
> 
> There I was thinking it's a quiet Sunday afternoon so why 
> don't I get out the LV-ROM player and see if I can do some 
> ADFS sector reading with it connected to the 1MHz bus.
> 
> I got out the Akhter host adapter, applied some power and 
> switched on and POP!  The capacitor went bang and the Beeb 
> didn't sound very happy either!
> 
> Unfortunately I had accidentally connected the 5V on the host 
> adapter up to a 12V supply, with "hilarious" consequences.
> 
> Thankfully the Beeb is OK but I think the host adapter is 
> dead.  Yesterday the Beeb was sticking on the "brrrrr" tone 
> with just "Acorn MOS" displaying but today there's no picture 
> at all, just the tone.
> It's fine without the host adapter connected but this happens 
> when it's attached and with or without power applied to the 
> host adapter.
> 
> Is it just the case of replacing the capacitor on the host 
> adapter or could I have blown some of the chips as well?
> 
> Just think what might have happened if I had had the LV-ROM 
> connected to the host adapter at the time.....
> 

Doh!

That sounds like a tantalum bead capacitor releasing its magic smoke.

You might be lucky, it depends on how quickly you removed the power.

The capacitor shorts out the PSU whilst it is liberating its magic smoke, so
if you were quick on the draw and removed the supply you might have saved
many of the ICs. But, if, like me, you have an industrial power supply, e.g.
50A at 12V then there just isn?t enough magic smoke to go around...

Most of the stuff on the host adapter is TTL, usually they try to
commuincate with their god with magic smoke after around 8 volts, but it
depends on the IC, I've had a circuit with a few gates, a couple of MSI Ics
7493/7447 etc. which ran grudgingly on 12 volts for 30 seconds, but smelt
rather bad :(

Just last week, a guy here connected up a Indium Gallium Arsenide (InGaAs)
sensor to the pinout of a Silicon sensor, a little click, alas, the magic
smoke left the device, never to return. Thing is, that sensor cost ?3,000...

Dave ;)