• Please review our updated Terms and Rules here
  • Exhibitor application for VCF West 2022 is now open! If you are interested in exhibiting, please fill out the form here.
  • Here are the results of the VCF East 2022 Post Event Survey: Survey Results

Repaired 5160 XT after -12V short

singlethread

New Member
Joined
Apr 12, 2020
Messages
1
Location
Netherlands
I want to give a big thanks to the maintainer and contributors of the minimum diagnostic guide at minuszerodegrees.net.
This guide provides exactly the information and step-by-step guidance I needed to repair my broken IBM 5160 PC/XT.

For the statistics: C58 was shorted on my mainboard.

In case anyone is interested in the details:
When I turned on my old XT for the first time in two years, exactly nothing happened. No sound, no lights, no fan. Upon closer inspection, I could see the power supply fan barely starting to turn at power-on, followed within 0.5 seconds by a click sound (as from a relay), then nothing.

I went about randomly disconnecting things and measuring voltages. Pretty soon I came to the incorrect conclusion that my power supply was broken.
While searching the Internet for ways to replace the power supply, I stumbled accross http://minuszerodegrees.net/5150_5160/MDC/minimum_diag_config.htm. The first sentence of that page "You are here because your IBM PC appears to be dead" had an immediate calming effect on me, like clearly this must have been written by someone who already knows what the problem is, and who will now explain the problem to me in simple words that even I can understand. And indeed this guide turned out to be everything I was hoping for. I quickly learned that a PC power supply can not be tested without an adequate load. Then I learned how to confirm that my power supply was in fact still fine, and that the problem was in the +/- 12 V lines on my mainboard. Indeed my multimeter measured 0.1 Ohm between -12V and GND. And upon visual inspection of C58, I could see just a tiny dark spot on the capacitor.

So I cut off C58, which eliminated the short in the -12V line. I decided to replace it with an aluminium electrolytic 10 uF 63 V capacitor. The guide recommends against resoldering on the board but I decided to try it anyway. Again I found that I was wrong and the guide was right: the solder job became a mess but in the end I got the new capacitor sort of soldered onto the pads.

And now my XT is fine again. It boots, it runs, and the harddisk makes its little musical sounds.
I'm very happy now. So thanks!
 

modem7

Veteran Member
Joined
May 29, 2006
Messages
7,789
Location
Melbourne, Australia
Welcome to these forums.

It is good to hear that you got your IBM 5160 operational.

There is lots other 5160 information at minuszerodegrees.net, kind of acting as a self-serve. For 5160 information beyond that, don't hestitate to open another thread. There are plenty of people here who know lots about the 5160.

Your 'C58' experience has been added to the list at [here].
 

Stone

10k Member
Joined
Nov 3, 2009
Messages
12,814
Location
South Jersey, USA
Kudos to singlethread for the excellent description of a very common problem that is so often misdiagnosed which can and does lead to confusion and unnecessary actions by so many with these older machines.

And, of course, thanks again to modem7 for having compiled and organized this wealth of information known as minuszerodegrees. I know I have had to refer to this invaluable site countless times.
 
Top