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IBM PC 5150 Blown Capacitor - Need to Replace?

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wesleyfurr

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Virginia, USA
As I mentioned in another thread, I'm working to get some of my old goodies out of the corners and get them up and running for a "show" the end of the month at a local retirement community. Among the items I want to show is of course my PC model 5150. I dug out a 5151 monitor and it worked (whew), turned it all on and I was grinning from ear to ear when it suddenly just powered off.

Started through troubleshooting and guessed perhaps it was the power supply...so I dug out an old clone machine (case essentially identical to the PC's and XT's)and swapped its power supply into the PC. Powered it on, fan spun, and I was promptly rewarded with a super-mini fireworks display, complete with smoke and all. Crap... Looked closer and found that the capacitor in the corner near the power supply connector and blown its lid. I tried the PC power supply attached the clone motherboard (which actually I had put in a 486DLC board years ago) and it fired up...ok, so PS is good. Put it back in the PC, and it fires up and works beautifully.

So...my question now...how critical is it that I actually replace that capacitor? Pretty comfortably my solder skills are up to snuff to do such a task, but on the other hand, why risk damaging things worse if it will work OK as-is? Same question about an old CGA/mono video card I have here with a blown cap...someone said just snip it off and don't worry about it (haven't tried that yet)...but is it OK to run without one?

I did a quick ebay search for replacement tantalum caps and have put in an order for 10 of them (16v 10uf) at a cost of like $2.50 or something...but of course now I'm concerned I didn't get the right thing...are all tantalum caps "polarized"? I'm not seeing anything in the listing photo indicating polarity...but it's also hard to tell. Item # 220653775284 for anyone who wants to take a look. Also, the PC motherboard uses the odd 3-legged capacitors, which I understand can be replaced with a 2-legged on as long as the center leg has the correct polarity. Any "gotchas" I need to watch out for? Assuming it really does need to be replaced?

Thanks in advance,

Wesley
 
No, you can replace that 3-legged one with a 2-legged one--the idea behind the 3-legged ones is that it's impossible to insert them backwards.

Or you can leave things as they are if you're happy with the performance. But if things get a little erratic and wonky, you should replace it.
 
Look at the solder pads. If it truly is the idiot-proof three legged one, than two of the legs should be going to pads that are connected. If it looks like the leads all go different places, you might have a problem. I don't have a schematic for the PSU handy, so...
You're basic tantalum cap is polarized. I didn't follow if the original one was electrolytic, or tantalum, but they do make two caps in a can three lead devices, and bipolar caps as well. I'd replace it. It's simple enough, and you can either attempt to figure out the actual purpose of the cap, and if can live with out it, or just stick a replacement in there.
patscc
 
So long as it works OK and doesn't hurt anything further, I'm happy to leave it alone.

I got some 16v 10uf tantalum capacitors in the mail from ebay today, and they are polarized, so I can give it a try if need be. From looking at the traces on the 5150 motherboard, I'm not sure that the outer ones are connected...hard to tell, I'm guessing if they are linked it is on a middle layer of the board, assuming it is multi-layer? This is on the motherboard, not the PSU...just near the power connections on the back corner of the board.

Thanks,

Wesley
 
The center lead on 3-lead caps is +, both outer leads are -.

You used to see this a lot on tantalums, because they'd complain with a loud "bang" if they were hooked up backwards. 3-terminal mounting makes this almost impossible.
 
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