Probabilities

I guess the question remains is, what did you use for replacement?

I can't see how they can go bad unless the leads eroded up inside the encasement.

On a sunny day (Sun, 07 Feb 2010 15:01:24 -0500) it happened Jamie wrote in :

Yes, possible, plastic transistors, but a short (varying say few hundred Ohm), resistance between collector and emittor... They hardly carry any current, 100k in series in one, reset circuit, the other one a few mA. But they are nice and dry.. do not look eroded either. Chip passivation?

On a sunny day (Sun, 07 Feb 2010 15:56:10 -0500) it happened Jamie wrote in :

LOL, yes, and BTW I replaced one with one of the same old ones, the other one I cut the wire to the collector, as it was hard to access, and already late.. ftp://panteltje.com/pub/board.gif ftp://panteltje.com/pub/wire_cut.gif Without the reset the thing works just as well... Will replace it some other time...

I have a bad batch of the MBT2222's at work that have little noise spurs at a specific current curve, no matter what type of circuit you put them in except for a digital switch. Acts almost like a tunnel diode. I keep them just to remind me how long it took to figure out why the circuit I used them in acted like our GOV. erratic..

I've used lots of BC548s and BC547s and never had a generic complaint. Maybe you just have a bad batch or even a counterfeit one.

Are your transistors actually 25 years old? Please test if the transistor case can be melted with a soldering iron. In 1993 a fire in the Sumitomo Chemical factory caused a worldwide shortage of epoxy encapsulation resin. Some of the replacement stuff proved to be of inferior quality and enormously increased the failure rate of the semiconductor devices.

Only a wild guess...

Piotr

already late..

Ha, I'm glad you can follow that pile of wires.. ;)

On a sunny day (Mon, 8 Feb 2010 03:04:29 +0530) it happened "pimpom" wrote in :

Yes so have I, but these are > 25 years old. The proability of 2 failing within the hour after so long, in totally different circuits, should be very small. To the extend I considered an outside EMP source, but then why only these? And no nuke was triggered here that I know about :-) Amazing coincidence!

On a sunny day (Sun, 07 Feb 2010 21:13:20 -0500) it happened Jamie wrote in :

Ohm),

already late..

Ya, this one was simple..... This is on the other side: ftp://panteltje.com/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_inside2_img_1757.jpg

On a sunny day (Sun, 07 Feb 2010 22:43:56 +0100) it happened Piotr Piatek wrote in :

Yes they can be melted!

On a sunny day (Mon, 8 Feb 2010 03:04:29 +0530) it happened "pimpom" wrote in :

Yes so have I, but these are > 25 years old. The proability of 2 failing within the hour after so long, in totally different circuits, should be very small. To the extend I considered an outside EMP source, but then why only these? And no nuke was triggered here that I know about :-) Amazing coincidence!

PS found an EMP source:

Sudden sunspot LOL Coincidence ?

Oh-oh. I hope I'm not falling into the habit of posting hasty replies without thinking. I noticed the "25 year old" term in your opening post, but thought you were referring to the age of the type. I remember vaguely wondering why you felt you had to mention that.

I too have batches of BC548s and related types that are at least

20 years old. They are more common that their JEDEC counterparts over here and I use them regularly. Never had a batch failure. I did have a batch of BA159 fast recovery diodes that tested OK with an analog multimeter, but quickly overheated and died in circuit.

Maybe you were asleep at the time :-)