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I/O card with apparent short...

S

Stone

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I have an 8-bit serial/parallel card that must be short since whenever I try to turn my XT on when it's in a slot the PSU powers down immediately. If I remove the I/O card and turn the XT on everything is normal. Is there a way to troubleshoot this I/O card? I don't have any idea what to look for or even if there is anything.
 
The first thing on my list would be to identify (with an ohmmeter) which rail is the culprit--in other words, is it the +5, +12 or -12 supply line? A card with a serial port on it will use all three.

That will considerably thin out the culprits. One of the more common failures is the destruction of the RS232 transmitters or receivers by a stray static discharge.
 
1) One cap is short. It's a K5M over 473. But there are three 3 lead caps. Two are short between 1 & 3 and one is short every which way.

2) +5 and +12 are short when the card is seated.
 
Stone said:
1) One cap is short. It's a K5M over 473. But there are three 3 lead caps. Two are short between 1 & 3 and one is short every which way.

2) +5 and +12 are short when the card is seated.
Click to expand...
Sounds like two bad caps, if I read right that the "one cap is short" is not the same cap as the "one is short every which way".

A short between 1 & 3 of 3-lead caps is OK; the outside leads are connected together so that it doesn't matter which way you insert it.

See:

http://www.vintage-computer.com/vcf...-IBM-CGA-Board&p=225881&highlight=#post225881
 
Yes, you read it right. The two lead is marked 'K5M over 473' and I have don't know the values for that. And one three lead is also short. It is marked '10-16' over a circled '2' and that is also something I am unfamiliar with.
 
2 lead - 0.047 µF
3 lead 10 µF, 16VDC

A two-lead cap will work just fine in place of the 3. The negative terminal can go to either of the outside points. The middle point is +.
 
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