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IBM 5150 PC system board repair

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ruthlessperson

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I have two systems boards from an IBM 5150 PC. They won't take any power if I connect a power supply to them the power supply just shuts down when I hit the switch. I don't know anything about troubleshooting this kind of stuff so if anyone has any ideals on how to fix these please let me know. Please try to explain things down to a newbie level. Thanks in advance.
 
ruthlessperson said:
I have two systems boards from an IBM 5150 PC. They won't take any power if I connect a power supply to them the power supply just shuts down when I hit the switch. I don't know anything about troubleshooting this kind of stuff so if anyone has any ideals on how to fix these please let me know. Please try to explain things down to a newbie level. Thanks in advance.
Click to expand...

Your problem may be that the motherboard itself doesn't use enough power in terms of what the powersuply expect.

The PSU is designed to automaticly shut down if not a big enough work-load is present. I don't remember how much work it needed in order to stay on, but one FH floppy disk drive is usually enough to get it running. It problably depends on the PSU too...
 
Hello there I had two junk 3.5" IDE hard disk drives connected to the power supply to combat this problem. I also tired removing the CPU and clock gen. IC and no luck.


per said:
Your problem may be that the motherboard itself doesn't use enough power in terms of what the powersuply expect.

The PSU is designed to automaticly shut down if not a big enough work-load is present. I don't remember how much work it needed in order to stay on, but one FH floppy disk drive is usually enough to get it running. It problably depends on the PSU too...
Click to expand...
 
You should check with multimeter all tantalum capacitors on your motherboards. I'm almost sure, one or more could have short. I had this problem on two of my XT boards, on CGA card and on Tandon FH floppy. On capacitors with three legs you should check for shorts between center (positive) and two outer (negative) legs.

R.
 
Hello yes, I do have meter, how do I use it and what do I check for?

Unknown_K said:
Do you have a meter so you can check the power lines to ground?
Click to expand...

Hello by a short do you mean setting the multimeter to continuity and seeing if I get 0's with the red lead on the center leg and the black on each of the outer legs, if it's good i should see some kind of number on both legs like maybe the same number?

CIPSTER said:
You should check with multimeter all tantalum capacitors on your motherboards. I'm almost sure, one or more could have short. I had this problem on two of my XT boards, on CGA card and on Tandon FH floppy. On capacitors with three legs you should check for shorts between center (positive) and two outer (negative) legs.
Click to expand...
 
ruthlessperson said:
Hello by a short do you mean setting the multimeter to continuity and seeing if I get 0's with the red lead on the center leg and the black on each of the outer legs, if it's good i should see some kind of number on both legs like maybe the same number?
Click to expand...

Basically, yes. If it's shorted you'll get 0. If not shorted, it will show "infinity" or no number at all.

It should be set it to 2M Ohm, or the higthest setting for resistance it got.
 
ruthlessperson said:
Hello by a short do you mean setting the multimeter to continuity and seeing if I get 0's with the red lead on the center leg and the black on each of the outer legs, if it's good i should see some kind of number on both legs like maybe the same number?
Click to expand...

My multimeter doesn't have continuity setting, so I use resistance setting. With capacitor soldered on, the multimeter will probably show higher or lower resistance, but when it shows almost no resistance, the capacitor could be damaged. There are two types of tantalum capacitors on old IBM boards - with two and with three legs. You schould check all of them.

R.
 
HI I have found a few of these caps that read all zeros on this meter. I guess the next step would be to remove them from the board and test them.

Were can I order these three legged and two legged caps new?

Thanks and have a nice day.
 
Tantalums on 5150 motherboard

Tantalums on 5150 motherboard

The likelihood is high that only one of those tantalum capacitors is short. They all measure as short because they are in parallel.

The double-legged tantalums have polarity. They need to be inserted the right way. The triple-legged tantalums can be inserted either way. You can substitute the triple-legged variety with the double-legged variety, but make sure that the capacitor is inserted correctly, positive leg in the middle hole and negative leg in one of the outer holes.

The tantalums on the 5150 motherboard are 10 uF, 16 volt.

The double-legged variety should be easily obtained at an electronics shop.

The triple-legged variety are (or were) available at Mouser Electronics. The item details for the Mouser part are:
Mouser part number: 80-T398E106M16AT
Manufacturer part number: T398E106M016AT
10/16V TRIPLE LEAD
Kemet Dipped Radial Tantalum Capacitor​
 
Sometimes the leads on the two leg capacitors are long
enough that you can just unsolder one leg, and tilt the capacitor
enough to remove that leg from the circuit. This way you can
test the capacitors to see which ONE is shorted. Just be careful
when you put the leads back through the board, its easy to damage
the solder pad.
 
Hi all, I need to brush up on my soldering skills before I began to unsolder and solder anything, Have not picked up a soldering iron in at least 30 years and even back then I was not that good at it.

I am using a solder sucker, and a Weller iron with a tip temp of 650. I hope that's the right setup for the job. I have not had an luck with braid. I been "practicing" on a junk clone mother board.
 
If your braid (e.g. soderwick) is old, it might pay to get 'fresh'. I've found that braid gets less effective with age. Certainly, any I've had for more more than ten years is next to useless.

If you haven't already, do a good visual inspection of the tantalums because sometimes when tantalums go short, they present a small black patch as shown in this photo:
http://members.dodo.com.au/~slappanel555/misc/bad_tantulum.jpg
 
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