View Full Version : Exploding Osborne 1!

October 2nd, 2007, 12:41 PM
Hi, I've moved this from the "Introductions" forum, where I posted for the first time yesterday. There i mentioned an Osborne 1 I acquired which blew a couple of capacitors when I first switched it on. Chuckmagee says...

And I have already posted my experiences with exploding tantalum caps. A common thing in *vintage* land.

Yes, it's the first time I've seen it happen and it was an alarming experience. A loud "pop", then a sizzle, then white acrid-smelling smoke issuing from all orifices in the machine.

Not a pretty sight!

Being a non-techie, I didn't actually KNOW what had happened until I went on the web and discovered this is a rather common occurence with things that have been at rest for a decade or two. Strange thing is the machine appeared to still be working even with all this smoke pouring out of it. At least in the 1 second it took for me to get to the wall switch! The screen display didn't disappear.

I found out that the blown ones (they were old paper caps) were designed to reduce radio interference, so perhaps they weren't critical. However, it was after I replaced them, that the things REALLY didn't work!

The behaviour is a non-boot with garbage on the screen but this is sometimes accompanied by random spinning drives (usually BOTH drives). The behaviour can differ every time I switch it on. Sometimes the drives just don't activate at all. Sometimes the drive lights flicker on and off very fast.

I'm wondering if it is a short somewhere? I'm sure the replaced capacitors are the correct type. Does anyone recognise these symptoms, or could they be almost anything?

I'm can see I'm going to have to arm myself with some test equipment (then learn how to use it!).

October 2nd, 2007, 01:02 PM
Sounds like it's just running through whatever junk comes up on the RAM chips. Computer designers love to use "memory mapped i/o". I guess it's easier or something. Anyway, as it travels along excuting junk, it hits those magic addresses. Oooooo, the drives think it's command time. Click, thud, whir. Sometime later, here comes the runaway crud again, click, thud, whir. Of course, the crud changes randomly with each power up. Sometimes it can be executed, sometimes not.

October 2nd, 2007, 01:06 PM
Right. I understand what you mean. Could be. Thanks.

October 2nd, 2007, 02:05 PM
LOL, my TRS-80 Model 4 is doing the exact same thing. I should really get it repaired...