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5150 Shorted cap on the 12v Rail.

D

dabone

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Feb 26, 2009
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Chattanooga, TN - USA
My 5150 started acting up, and it ended up being a shorted 12v cap. I've clipped it and was wondering if when I replace it, should I just shotgun the entire board.

16-64k board, so can I replace all the caps with 10uf 16v?

Thanks,
later,
dabone
 
I would just replace the one that shorted, Chances are the rest will be fine.
 
Nah, I'm going to replace most of them while I have it out. The current one that failed worked fine for me for 20 or 30 hours of use and then failed, so the other ones will follow.

Later,
dabone
 
dabone said:
The current one that failed worked fine for me for 20 or 30 hours of use and then failed, so the other ones will follow.
Click to expand...
Not only can't you say that with certainty but I don't think there is any way to predict what you have just stated.

FWIW, I replaced that 12V tant five years ago on my 5160 and none of the others have followed suit in the ensuing five years.
 
Stone said:
Not only can't you say that with certainty but I don't think there is any way to predict what you have just stated.
Click to expand...

Agree totally. I've replaced lots of caps on the same voltage line without replacing any of the others. 5+ years on a lot of things without any problems. Unless there's a known bad batch of them, then it's just wasted $$$.
 
On the last 2 compaq portables I've worked on I had multiple failures on these tantalums. Motherboard and video card, plus floppy controller.

Looking at minuszerodegrees we see that the caps are one of the most common failure points. And considering I can get 50 of them for $13 I don't really see a large expense.

Are you recommending not replacing because of risk to the board? Or just couldn't be bothered to replace the other ones until they short?



Later,
dabone
 
I'm a firm believer in... 'If it ain't broke; don't fix it.'

I'm sure if you continue to fix things that don't need fixin' you'll soon figure it out.
 
I would check the voltage rating on the caps and make sure that they are 12V. I've had a few motherboards stuff 5V caps in a 12V rail at manufacturing. They obviously fail more often, and should be replaced.

However, I have to agree with others on this thread. Typically when a tantalum shorts, it is a defect in that specific capacitor. The others will still have a long lifetime. The only time I wholesale replaced all tantalum caps on a board is when I found the out of spec caps noted above.

Chris V.
 
+1 on don't replace the non-exploded tantalums

you could make an argument for shotgun replacement of electrolytics because the electrolyte can dry out and/or leak (I still don't do that either) but tantalums either explode randomly or work forever
 
The only time I ("summarise"?) replace condensers without specifically testing them is when there are a large number of large electrolytics in something that I already know has multiple bad ones.

I'm listening to the Pack make that Minnsota team look silly right now on a 72 year old receiver with all original parts.
 
maxtherabbit said:
+1 on don't replace the non-exploded tantalums

you could make an argument for shotgun replacement of electrolytics because the electrolyte can dry out and/or leak (I still don't do that either) but tantalums either explode randomly or work forever
Click to expand...

I 90% agree, but I have had a few machines that have had to have multiple removals.

One was my 5160 640K, originally had to remove a couple on the motherboard, then about two years later had one go bad on the serial board, then a few months later one on the CGA card went. It's been fine since. All on the +12 or -12V lines. I only remove/replace on failure though.

Then I have a 1982 5150 model A that's still 100% untouched and runs fine.

Seems to vary a lot.
 
maxtherabbit said:
you could make an argument for shotgun replacement of electrolytics because the electrolyte can dry out and/or leak
Click to expand...

This I definately agree with. I do this and found many times a cap which looked perfectly normal but after removing them discovered they had started leaking underneath or dried out to the point where one of the legs came completely off with very little force.
 
Tantalum capacitors don't have a wet electrolyte, they can't leak, they just explode randomly.

I'd recommend against shotgun replacing them as well, if they're not bad, leave them alone. I used to be of that mindset, but after one too many botched mass replacement sessions, I've decided to leave stuff alone that isn't going to cause damage if left alone if it still works.

If OP does decide to do it anyway, I'd recommend that you only do a few at a time and test the board between batches. This way if you got something wrong and the board doesn't power up, you have a smaller area of the board to troubleshoot.
 
So, I think I am in the tantalum cap problem zone as well. What I can't find anywhere is how to figure which cap is bad. Any input?
 
Dwight Elvey said:
I'm not sure how that leads one to the faulty capacitor?
Click to expand...
The page links to many other pages. Which pages a user is taken to depends on their answer to questions.

As an example, let us assume that a user has a 5160 motherboard on which capacitor C58 is short-circuit, and the capacitor has no visual indication of failure.
The navigation in that case would be:

1. On start page: [Click here if you did not hear the beeps.]
2. On page taken to: [Click here if the power supply fan turned for a fraction of a second and then stopped.]
3. On page taken to: [Click here if the power supply fan is now turning (continuously).]
4. On page taken to: section [5160 motherboard (XT)]


The subject pages have been slowly expanded over the years, with more improvement to come.
 
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