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5150 Shorted cap on the 12v Rail.

Stone said:
The process it outlines is simple and straightforward. It is quite easy to carry out and has led me to the offending component every time I have used it. Kudos to modem7.
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Locating a capacitor shorted on a power rail is not the same as locating a faulty RAM or interrupt controller.
Isolating the faulty power rail doesn't take much effort. Locating which is the bad capacitor is not the same thing, assuming it is the capacitor.
In any case, the pointers no longer work. I suspect too many people picked them.
Dwight
 
Dwight Elvey said:
Isolating the faulty power rail doesn't take much effort. Locating which is the bad capacitor is not the same thing, assuming it is the capacitor.
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There's nothing to assume here.

You know you have a short on the 12V rail.

Modem7's guide points to a suspect tant.

You remove it and find the short is no longer there.

Problem solved.

Simple and efficient.

As I previously stated I've used it several times for this problem with success.
 
dabone said:
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
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So I've seen multiple references to clipping a tantalum on a power supply to get it working again. Please excuse my ignorance, but does that mean literally cutting it out and not replacing it? I assume you have to install a patch wire or something to complete the circuit?

Just want to learn.
 
There are many instances where simply removing a shorted cap will allow a previously non functioning piece of equipment to work, albeit minus the filtering capability of that removed cap.

BTW, a patch wire is a short -- no different from a shorted cap. :)
 
Hey guys. My trouble is with an IBM clone with a blown tantalum on the floppy controller board, but since we're on the topic of tantalums...

Can you spot the bad component? :eek:
IMG_1974.JPG

Trying to decide whether or not to recap the other 3 tantalums at the same time. The remaining 3 caps are marked 10uF but they show as 28uF on my Peak ESR70 with ESR ~1.4 ohms. Can higher tantalum capacitance also mean a cap is going bad?

IMG_1975.JPG

These readings are while testing in-circuit. I plan to remove and test them and test this weekend, but thought I'd ask before I go to that trouble.
 
normanator said:
These readings are while testing in-circuit. I plan to remove and test them and test this weekend, but thought I'd ask before I go to that trouble.
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Which accounts for your readings. Depending on your preferences, I'd probably not bother to fix anything that's still working. For the larger values (>10 µF), you can also use electrolytic caps, since the purpose in most of these is decoupling.

There seems to be a school of thought that re-capping everything in site will fix all problems. While that may be true of the systems with the 90s capacitor disease, it's not likely to resolve many problems.
 
Makes sense. And I can see in this thread the general consensus is replace the bad and leave the others alone. Will go with the group recommendation.

Noticed the blown cap is the gateway for +12V coming from the ISA bus connector onto the ground plane (grid) you see in the first pic. This cap has a twin in the middle of the plane that channels the 12V- back out. Looks like the blown one is upstream and catches the brunt of anything nasty coming from the bus. Originals are 16V, but all I have handy are 25V 10uF so I'm going to use that. Thanks again.
 
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