PDA

View Full Version : IBM 5155 started smoking



XDUR
April 8th, 2017, 01:37 PM
So today I found some MS-DOS driver to access an SD card via parallel port on this forum and I was starting to copy the driver to a floppy disk, when suddenly something started smelling funny in the room. Then I saw smoke coming out of the back of my IBM 5155. I jumped up and quickly turned it off.
After taking a peek inside the PSU, I notice some capacitor/filter has burst.
I'll pop it open tomorrow to check what part I need to order. Let's hope nothing else got damaged. I was still running while it was smoking so I guess it will be ok.

37663

modem7
April 8th, 2017, 02:41 PM
After taking a peek inside the PSU, I notice some capacitor/filter has burst.
This is a common failure, in many types of vintage computers.
Refer to the 'Line Suppression Capacitor' section of the web page at [here (http://minuszerodegrees.net/failure.htm)].

modem7
April 8th, 2017, 04:15 PM
Within my spare 5155 power supply, I found an [X2][250 Vac][0.22 F] line suppression capacitor in that position.
Photo at [here (http://minuszerodegrees.net/temp/3/temp_726547128332611563.jpg)].

XDUR
April 9th, 2017, 12:18 AM
Thanks for the information. I do see some other values on the picture I've taken (25/085/56 instead of 40/85/21), but I guess those don't matter too much.


Within my spare 5155 power supply, I found an [X2][250 Vac][0.22 F] line suppression capacitor in that position.
Photo at [here (http://minuszerodegrees.net/temp/3/temp_726547128332611563.jpg)].

XDUR
April 27th, 2017, 01:43 PM
Ok, so today I wanted to replace the capacitor but I have one problem. The PCB is riveted onto the metal case.

37986

Any idea how to detach the riveted PCB without doing damage?

I found some topic about someone that hacksawed the PCB out, but that seems a bit drastic to me.
http://www.classic-computers.org.nz/forums/viewtopic.php?f=11&t=2166

lutiana
April 27th, 2017, 01:54 PM
You'll have to drill them out and replace them when you are done. Or better yet drill them out and see if you can replace them with a small nut and bolt.

flashedbios2012
April 27th, 2017, 03:39 PM
I didn't think that defective capacitors were an issue with computers until 1999 to about 2006 with that capacitor plague involving the "stolen forumula" and cheap chinese caps. Otherwise, aren't they supposed to last forever. They are a non moving component.

roberttx
April 27th, 2017, 04:10 PM
Otherwise, aren't they supposed to last forever. They are a non moving component.

Ceramics can last, but 'lytics, wax paper, etc always fail eventually. That's true of radios and amps that I have dating back to the 1930s, long before events that you refer to.

Stone
April 27th, 2017, 04:41 PM
Not only that but older tantalums are always looking for a reason to explode.

SGTSQUID
April 27th, 2017, 08:50 PM
Have you tried Nicorette?

GiGaBiTe
April 28th, 2017, 09:53 PM
Ceramics can last, but 'lytics, wax paper, etc always fail eventually. That's true of radios and amps that I have dating back to the 1930s, long before events that you refer to.

Wax and paper capacitors of any type have long since expired and should always be replaced. The paper inside goes acidic and the capacitor starts leaking DC across it, causing all sorts of havoc. In old tube equipment, they can red plate tubes and burn out transformers and chokes in a hurry.

The newer aluminum electrolytic style caps have a life of about 10 years in climate controlled storage and less if regularly used due to heat.

ejs
April 29th, 2017, 11:56 AM
Ah, one of the infamous Rifa caps. I had one fail in my Apple ][+ and one of my Integral PCs.

These are "safety" capacitors (so called because they are supposed to fail in an open circuit, and are thus rated to be connected directly across the AC line). They are metallized paper, meaning the dielectric is paper with a thin metal electrode deposited on it (the capacitor is also impregnated with a flame-retardant epoxy). They are also self healing, so if a short develops inside the capacitor, it burns out a small section of the deposited metal and clears out a non-conductive area around the short.

Last week I had a chat with a rep from a German capacitor manufacturer and showed him one of these burned Rifa caps. He said that this is a common failure mode. They are allowed to fail in this way--they will emit a lot of smoke but they should not flame up. Eventually they carbonize but they should remain open-circuited. He also said that they had to move their testing outdoors because the smoky smell tends to linger for so long. I think it smells just like a campfire.

One thing that came up in our discussion that is of special interest for computer collectors is that these film capacitors last longer if they are powered up. They have a storage lifetime of about 5-10 years. I believe the reason is that you need to periodically clear out the tiny shorts that develop in the dielectric layer over time.

So there's another good reason to occasionally turn on machines in your collection...

XDUR
April 29th, 2017, 02:15 PM
Thanks for the info about the RIFA caps.

I've managed to drill/crack out the PCB and replace the bad cap. Such a hassle.

I did damage a trace pulling out the bad cap, but I just created a bridge and that was fixed.
38141

I should also have replaced the other RIFA cap, but that's for another time.
My 5155 still works, so that's great :)