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IBM CGA Card Oddity in 5150

lyonadmiral

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I had purchased an IBM CGA card a while back, NOS, still in antistatic wrap, the whole thing looked & looks kosher. I installed it into my 5150. I switched the jumpers. Powered up, nothing. First I thought blown power supply, motherboard, but after troubleshooting it is indeed an issue with the video card. Assuming, it really is NOS, what could be wrong with the card and is it even possible to fix?

Thanks,
Daniel
 
Problably a dry capacitor. Most of the problems with old electronics doesn't come from use, but rather age alone.
 
I agree with PER. I've seen two IBM CGA cards with shorted caps on the +12v line and in both instances the computer would not power up with the offending CGA card installed, but once the bad cap on the +12v was removed, they both worked fine. See this post.
 
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I agree with PER. I've seen two IBM CGA cards with shorted caps on the +12v line and in both instances the computer would not power up with the offending CGA card installed, but once the bad cap on the +12v was removed, they both worked fine.

Removing the capacitors completely or replacing them? How would I test?
 
Removing them (one leg is sufficient) one at a time would reveal the source(s) of the short. Then you'd know which one(s) to replace.
 
Removing them (one leg is sufficient) one at a time would reveal the source(s) of the short. Then you'd know which one(s) to replace.

Could I use a multimeter? I assume if the capacitor has lost its electrolyte it would probably not let any voltage pass through it?
 
With the card removed, I think you could check for short with a multi-meter to see if the 12v line is shorted to ground. Or Remove C8 and try it again. If it works then replace with a new cap when you can but don't worry to much about it. The card seems to work fine without C8. See This Post
 
With the card removed, I think you could check for short with a multi-meter to see if the 12v line is shorted to ground. Or Remove C8 and try it again. If it works then replace with a new cap when you can but don't worry to much about it. The card seems to work fine without C8. See This Post

It's what I get for never finishing the basic electronics course in vo-tec. :) I'll give it a try and see what I find. Thanks guys.
 
It's even easier to tell with the card in the slot. Just check the PSU connector on the motherboard. There's plenty of 12V and ground terminals there. :) While you're there you can check for a 5V short too, 'cause you never know.
 
It's even easier to tell with the card in the slot. Just check the PSU connector on the motherboard. There's plenty of 12V and ground terminals there. :) While you're there you can check for a 5V short too, 'cause you never know.
But, with the card installed, the short could be elsewhere. With it removed, one can isolate the short to the CGA Card. A quick google search should help determine which contacts to check on the 8-bit card edge connector.
 
But, with the card installed, the short could be elsewhere. With it removed, one can isolate the short to the CGA Card. A quick google search should help determine which contacts to check on the 8-bit card edge connector.
DUH... an initial test of the 5V and 12V terminals without the card inserted (SOP) would remove that as a possibility. :)
 
So I'm going to finally get chance to get the multimeter out tomorrow, both time and necessity are forcing me to it, I've got a picture here, can anyone point out or (copy the picture) and circle possible culprits?

Thanks,
Daniel
IBM CGA.jpg
 
.... can anyone point out or (copy the picture) and circle possible culprits?

Thanks,
Daniel
In the upper right hand corner is a three legged tantalum cap labeled C8 on the card. That is the one that was shorted on both of the CGA Cards that I had mentioned earlier. This is the only one that I have found defective on my CGA cards. Your results may vary.
 
The circuit diagram shows that of all the tantalum capacitors (all of value 10 uF), C8 is on the +12V line, and the remainder are on the +5 volt line.
Based on that and on experience, C8 is the most likely one to fail.

In the upper right hand corner is a three legged tantalum cap labeled C8 on the card. That is the one that was shorted on both of the CGA Cards that I had mentioned earlier. This is the only one that I have found defective on my CGA cards. Your results may vary.
In May 2012, member CannedBread also had C8 on his IBM CGA card fail.
 
In the upper right hand corner is a three legged tantalum cap labeled C8 on the card. That is the one that was shorted on both of the CGA Cards that I had mentioned earlier. This is the only one that I have found defective on my CGA cards. Your results may vary.

If I remove it, how immediately must I replace it? I just need to get it going long enough to test an extender card since I have no display and need the RCA output on the CGA card.
 
In May 2012, member CannedBread also had C8 on his IBM CGA card fail.

C8 blew up on my CGA card too. I still have the black burn mark on the inside of the case to prove it. :)

Replacing that cap is not critical. The card will still work perfectly fine without it. All it does is help filter the DC power rail -- which, as long as your power supply is in good health, should be already pretty clean and ripple-free.
 
C8 blew up on my CGA card too. I still have the black burn mark on the inside of the case to prove it. :)

Replacing that cap is not critical. The card will still work perfectly fine without it. All it does is help filter the DC power rail -- which, as long as your power supply is in good health, should be already pretty clean and ripple-free.

Some appear to be bulged on my card, but none seem burned or give off that aroma. Do I snip the entire capacitor off, just 1 leg, or two legs?
 
You can snip the middle leg of the cap if you don't want to remove it entirely. The idea behind the 3-legged cap was that the outer leads are connected together internally, so it's impossible to insert the cap backwards. (Perhaps I should say "nearly impossible"--there's always some guy who will figure out how to do it.) It can be replaced by a 2-terminal cap without damage.

Largish tantalum caps (and electrolytic for that matter) are used for "decoupling"--to make sure that local current spikes don't propagate and cause mayhem (think of them as shock absorbers). Small caps, usually across each or every other IC are used for "bypass"; shunting high-frequency noise to ground.
 
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