• Please review our updated Terms and Rules here

Osborne 1 started on Fire. Barbecue time!

eXTended8088

eXTended8088

Experienced Member
Joined
Apr 5, 2008
Messages
86
Location
Central PA/Upstate NY
Hi All :)

Just today, an acquaintance gave me an Osborne 1 missing it's CRT that he recently acquired but did not test. I wanted to see if it would power up and when I plugged it in and turned it on, It made a small beep sound, but nothing else happened. No drive lights no fan spinning, no nothing. It left it on to see if it needed to wam up or what not, and about 7 minutes later massive and mean massive amounts of smoke came out. I ran over and shut it off and unplugged it. Any idea what the heck might of happened. It smells like roasted marshmallows! I let it "cool off" for a bout a half hour then turned it on quickly to see if that "beep" was still present, which it is. I then quickly tunred it back off and unpluged it. Just curious if this has happened to anyone else. I searched the net about it and found a short video on youtube but thats about it.

Thanks for any help! ;)
:eek:nfire:
 
Hi,

Mine did the same but without the smoke. It was a capacitor in the PSU and was an easy repair.

It's quite common for capacitors to fail after years without use. They can leak or dry out but either way they need replacing.



Cheers,

Andy.
 
Specifically, it is very often one of the line filter capacitors. rectangular resin-encapsulated things. Search the forum for "Rifa".

After all, isn't that what you do with Rifas? Smoke them, that is.
 
Thanks All :) I was also reading Mr. Tezza's blog entry from 2008 where he was dealing with this very same issue.

http://www.classic-computers.org.nz/blog/2008-12-06-osborne-repair-1.htm

My Osborne is in horrible shape. Missing screws, 1 hinge busted off, completely missing CRT, missing knobs for controlling the brightness and contrast, power supply metal panel completely hanging off and not screwed in, etc.. etc.. I opened it up and got the 2 full height 5.25 floppy drives (Siemens FDD 100-5) out of there. They look beautiful. I'd love to use them in my IBM PC, but the connections are not the same. The mainboard and the keyboard look excellent as well. I'll probably end up putting everything else in my scrap pile. If anyone needs these floppy drives or the MB or KB let me know. Another weird thing is my Osborne has a fan in the back but it is NOT an Osborne Executive. Maybe they used the back of one for this in a pinch. No idea.
 
eXTended8088 said:
...My Osborne is in horrible shape...I'll probably end up putting everything else in my scrap pile...
Click to expand...
Before you scrap it, please offer it to some of the Osborne owners as a for-parts unit. It would be worth shipping to Osborne owners.

Also as you mentioned, the Siemen drives in the Osborne had their drive electronics replaced with one designed by Osborne; not compatible. Those electronics boards and drives could enable some Osborne owner the get some drives running again.

Its sad that there is so much wrong with that Osborne... if you decide not to restore it... at least make it available to help other Osborne restoration projects.
 
JDallas said:
Before you scrap it, please offer it to some of the Osborne owners as a for-parts unit. It would be worth shipping to Osborne owners.

Also as you mentioned, the Siemen drives in the Osborne had their drive electronics replaced with one designed by Osborne; not compatible. Those electronics boards and drives could enable some Osborne owner the get some drives running again.

Its sad that there is so much wrong with that Osborne... if you decide not to restore it... at least make it available to help other Osborne restoration projects.
Click to expand...

The only things I considered scrapping were the plastics as they are in horrible shape, except the faceplate. Everything else I usually put to the side to either give away or barter for. Very rarely do I ever toss anything.
 
eXTended8088 said:
Thanks All :) I was also reading Mr. Tezza's blog entry from 2008 where he was dealing with this very same issue.
Click to expand...

Yes, by sheer coincidence I was using my Kaypro II yesterday and it also went all fizzy and smokey on me. I'd actually replaced all but one of those PSU line filter caps. However, this was the (large) remaining one I hadn't got around to replacing.

This one really made a mess, with quite a bit of liquid resin over the circuitboard.

2014-09-08-blown-psu-cap-kayproII.jpg


An easy fix though. I had a replacement in the spares box so within an hour the Kaypro was up and running again.

Moral of the story. Replace ALL these old line filter caps when you have the machine open because it's highly likely they are all ready to fail.

Tez
 
Chuck(G) said:
Is this failure more common on units that operate on 220V rather than 120V?
Click to expand...

You may be right. Certainly nearly all machines I have with these kinds of caps have blown at least one, apart from those where I've carried out a pre-emptive strike and replaced them all before-hand (like with my TRS-80 Model 4) .

I might have a couple of Apple II PSUs with their original caps but that's about all.

Tez
 
Chuck(G) said:
In the 220V models, what's the voltage rating of the caps that went kablooie?
Click to expand...

I'm not sure Chuck. They have been tossed. I'll try and salvage the latest one from the bin and take a look (if any of the specs are still visible anywhere).

Tez
 
Tez, it just occurred to me that a lot, if not most, of these supplies can be configured as 120V or 220V line-operated supplies. It could be that the Rifas were simply under-rated for 220V application. That could provide a caution to those whose line supplies are 220V with any of these caps installed, but not yet smoked.
 
What I was thinking is that they may well be properly rated for 220V, but just last longer on the 120V configuration.

Even if they aren't 110/220 switchable, they may have been designed as 220 and built as 220 or 110, hence the same voltage rating on the capacitors. (I'm guessing, I never paid that much attention to the capacitors in these power supplies because I haven't had trouble with them)
 
I don't think that the common failure of these Rifa EMI filtering caps is a matter of insufficient voltage rating. These are metallized paper dielectric caps, and the paper dielectric is prone to moisture absorption if the case is not perfectly sealed. Most, if not all, of these decades-old Rifa EMI filtering caps that I have seen have visible cracking of the plastic cases. My hypothesis is that over the decades, the plastic cases crack, then atmospheric moisture gradually seeps in, and that moisture absorption lowers the breakdown voltage of the dielectric to the point where they catastrophically fail once power is reapplied.

I replace them with either metallized polyester or metallized polypropylene caps with similar ratings. Most importantly, they're caps of the same safety class. I figure that poly film dielectric is much less prone to moisture dielectric even when not in sealed cases, so they shouldn't exhibit this particular catastrophic failure in a few more decades.
 
NF6X said:
I don't think that the common failure of these Rifa EMI filtering caps is a matter of insufficient voltage rating. These are metallized paper dielectric caps, and the paper dielectric is prone to moisture absorption if the case is not perfectly sealed. Most, if not all, of these decades-old Rifa EMI filtering caps that I have seen have visible cracking of the plastic cases. My hypothesis is that over the decades, the plastic cases crack, then atmospheric moisture gradually seeps in, and that moisture absorption lowers the breakdown voltage of the dielectric to the point where they catastrophically fail once power is reapplied.
Click to expand...

I think that thermal stresses play a big part in the failure. I've got a big container of NOS Rifas that I picked up at one of Halted's parking lot sales in the early 80s. They range in value from about .001 uF to 2uF and they all look just fine. A random check with a meter shows no measurable leakage in any of these things. I recently replaced the ignition "condenser" in a chainsaw (Stihl) with a 400V one and it works just fine.
 
I suspect that you're right about thermal stresses. If my hypothesis is correct, then I wouldn't expect to see many catastrophic failures of these caps if their plastic cases are still in good condition; it's just that most of the ones I've encountered so far have had lots of visible cracking of their plastic cases, and that might have been caused or accelerated by storage conditions over the years.

I'd imagine that it would be possible to rejuvenate one of these caps (prior to catastrophic failure, that is) by baking out any moisture and then vacuum impregnating some sort of sealant to close up the case cracks, but it's just so much easier to replace them with new caps that aren't prone to moisture absorption in the first place.
 
Interesting to note are failures of the tantalum capacitors on the IBM 5150/5155/5160 motherboards, reported by VCF members, and recorded at [here].
IBM used the same 10µF/16V rated caps to filter both the 5 volt and 12 volt lines, but the (reported) ones failing are the ones on the 12 volt lines.
 
Chuck(G) said:
In the 220V models, what's the voltage rating of the caps that went kablooie?
Click to expand...
The 220V models have the same rating RIFA @250VAC.
I think the cracks are not related to storage/age. Cracks appear while little shorts expands the inner structure and then perhaps opens the moisture the way into.
RIFA Data sheet
Frank
 
Last edited:
You must log in or register to reply here.
Back
Top