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IBM PCXT Short

AgentOrange96

New Member
Joined
Jul 24, 2014
Messages
9
Hello,
I have had my grandfather's IBM PCXT for quite a while now, but I've never gotten it to boot. It doesn't even post or spin up the hard drive normally. I have found out from this web page that the power supply will not provide power if it detects a short. So, to check this, I simply unplugged the power to the motherboard and so the power supply is only connected to the hard drive. In this case, the hard drive spins up. From this observation, I am pretty sure the issue is caused by a short somewhere on the board. (Also I have tried the board with no expansions on it at all) What I'm wondering is if there is any better way to try and find said short than removing each capacitor one by one and testing them? I'd rather not be taking that much stuff off the board for fear I won't re-solder it in right. If there is no better way, would there be any indications as to where I should start looking first? (IE where maybe this happens more often?) I'd really love to get this machine running, so thanks in advance for any help I can get!
 

tingo

Veteran Member
Joined
Aug 12, 2009
Messages
1,480
Location
Oslo, Norway
Have you tried measuring the voltages on the motherboard when the PSU is connected and powered up?
 

Stone

10k Member
Joined
Nov 3, 2009
Messages
12,814
Location
South Jersey, USA
It shouldn't be too difficult to determine whether there is a short in the 12v line on the motherboard. Using a short tester of your choice check the 12v pin to a ground pin. If it tests short you will have isolated the problem to one circuit.
 

ibmapc

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Apr 5, 2010
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Albany, OR USA
...I'd rather not be taking that much stuff off the board for fear I won't re-solder it in right. ...
If you're serious about playing around with old computers, you really need to practice your trouble shooting and soldering skills. I recommend a half way decent digital multimeter and a 25 watt radio shack soldering iron. Then go to Goodwill and buy some cheep old electronics(something with a pc board) and take it apart and practice removing and replacing components. Also, Radio Shack has some simple kits that require basic soldering skills, but they are pretty easy and don't require removing and replacing parts, unless you make a mistake during assembly. After practicing for a while, you just might find that repairing your XT won't be that scary.
 

AgentOrange96

New Member
Joined
Jul 24, 2014
Messages
9
Hi,
I actually identified the capacitor that was an issue by the fact that it was clearly burned and I replaced it. So, now the board is powering up, but it isn't posting. I suspect the RAM. I've reseated bank 0, which as long as the dips are set right is the only bank that matters. I'm in the process of swapping it out with bank 1 to see if that will work. Unless there's a way anyone knows of to test individual RAM modules to see if they are good. Thank you for your replies so far!

As for soldering, I have soldering equipment, and I've done it before, I just don't trust my own soldering nearly as much as IBM's. I'm terrified to replace the dock connector on my iPod, but I'm gonna have to at some point, but that's another story altogether. :p
 

NeXT

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Joined
Oct 22, 2008
Messages
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Location
Kamloops, BC, Canada
My guess is a tantalum cap has shorted but the PSU doesn't have enough of a kick to blow it open. If you like the adrenaline rush you can substitute in a beefier PSU and force it to blow open.
 
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