View Full Version : i have an osborne 1 computer that started smoking

February 28th, 2017, 05:44 AM
hi all i had an osborne 1 computer that when turned on the disk drives keeped spinning then turn it off finally i got a green screen with a lot of 0's and junk on screen then next thing computer started to smoke and i think something popped but i dont know what happened or what i can do i want to get it working again but dont know how to fix it is there anyone that knows how to restore it would love to find out or know what my options are am i better to just get another one off ebay working and spare my time i paid 120 for this one

February 28th, 2017, 10:32 AM
Hi rugbyguy,

The puff of smoke sounds like the classic problem of capacitors ageing and blowing in the power supply. This is a very common problem with machines of that age and is an easy fix. Replacements are easy to come by and if you are handy with a soldering iron it's a straightforward job.

As for the screen filling with 0s. That could be a little more complicated.

I had an Osborne for a while and during that time the capacitors in the power supply failed and I replaced them. A tantalum capacitor in the main logic board had also failed. If a capacitor fails on the logic board it could explain the other fault.

If it was mine, I'd unplug it, get the lib off and take a look inside. Be very careful in there of course as the CRT will hold a change for quite a while as can some points inside the PSU.



February 28th, 2017, 12:11 PM
Yes..those are the filter capacitor in the power supply unit. Our friend here at the forum "Tezza" has a great article how he fixed these and has even a picture in website (on this article).

I also did this kind of repair on my Osborne 1 a couple of years or so back. Did they ever "SMOKED"!! I found at least 2 of these kinds in my system so I replaced both.

November 9th, 2018, 01:35 PM
I have an Osborne 1 which I recently fixed up. I previously used it about 9 years ago, so before powering it up I replaced some capacitors on the power supply.

Here's how to get to the PSU board. Place Osborne top side down on a soft surface. Remove 5 bolts from what is now the top half of the case. Remove two video knobs (just pull off), the video pass-through plug, and unplug the keyboard. From the front bezel, remove the top three bolts, and loosen the bottom three. This is so you can pull the top of the bezel away from the top half of the case, which should lift straight out. Remove four bolts from metal brackets used to fix main PCB to chassis. Should now be able to waggle PCB away from bezel to reveal the base of the PSU, which has a plastic sheet covering it (see photo). Remove two screws holding PSU in, wires should all unplug.

As per Tezza's article there were three old Rifa X capacitors, one 0.1uF and two 0.01uF. The 0.1uF was starting to crack, the smaller ones were probably fine but I replaced all three anyway.

I also checked the electrolytic caps in the PSU with my LCR meter. The two mains smoothing caps (250V 100uF) were high ESR (1.0 ohm @ 1kHz) and one was slightly bulged so I replaced them with the same value but 105C (United Chemi-con KME series), the new ones had ESR of 0.3 ohm (at 1kHz) so should last a while. All the low voltage ones were fine (I think my Osborne has low running hours).

When I plugged it all back together, before powering on I turned the floppy drive spindles by hand (were a bit stiff), powered on and all was well. Booted from floppy on 2nd attempt (disk wasn't centred the first time), loaded CP/M and running fine, thankfully no issues. BTW my screen is black & white rather than green.