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precision 386 PCs

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josephdaniel

Experienced Member
Joined
Jul 3, 2012
Messages
317
Location
Florence, Texas, United States
I got this computer for free a few years agao didnt know anything about it at the time it's been sitting in a shed for the past two years. I got it out this past week the barrel battery had burst and corroded the corner of the motherboard under the power supply. When I got it out it would not post or anything but it would turn on and the lights and everything worked but when I hook up a hard drive it will not spin up unless I unplug the ribbon cable then it works fine. I took the board out and cleaned off the corrosion with a toothbrush and not the power supply just clicks very fast when turned on what do you guys think is wrong? it has a 50 mb hdd installed currently. It seems the onlything missing herre is a math co processor eveyh slot is full! 2012-07-05 17.13.59.jpg2012-07-05 17.12.25.jpg2012-07-05 17.12.43.jpg2012-07-05 17.12.57.jpg
p.s.anyone have any info on this computer I can't find anything about it.
 
Sounds like you don't know anything about AT type machines. First of clicking on an AT power supply usualy means a dead short... how did you plug the 2 AT power plugs cables back in (they have to be in a specific orientation)? Second old HD cables sometimes don't have a knotch for orientation, plug them into the drive backwards and it won't work. Leaking CMOS batteries usualy just take out the AT keyboard plug unless you have a board with RAM slots up close. You migth also have corrosion in the socket that holds the BIOS chip.
 
I tryed the powersupply in a 486 comp that I have and it works just fine. The corrosion is intwo of the expansion card slots even up inside of it and has started to work its way onto the bios chip wich is right next to the keybord connector.
 
I love those old 386's, they always had the best case. I picked one up almost identical to that one at a thrift store a few weeks ago.
 
Start by seeing if the power supply will run a hard drive by itself--no connections to the motherboard by either the hard drive or the power supply. If that's a go, let's continue.

Pull all of the cards out of the motherboard expansion slots. Make sure that the power supply is correctly connected to the motherboard and power it up. Do you at least get a beep?

Normally, corrosion by itself isn't enough to short a PSU. After you've cleaned the corrosion up, look at the motherboard where the corrosion was. Did it damage any traces? If so, you can usually jumper around those with small-gauge wire and some solder.
 
The power supply will power just the hard drive by its self . I just removed all of the expansion cards and tryed it agan nothing. But when I was pulling the cards I noticed a ceramic capacitor with the ceramic that is on the back missing exposing it's innards I will see if I can get a picture of it later.
 
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Yes, I own a multimeter and I checked a few of the badly corroded traces and two of them didnt conduct at all. I also found a busted ceramic cap witch I know is very unusual for a ceramic cap I learned this from my experience with antique radios.
 
Take a resistance reading in both directions on the +5 and +12 pins on the motherboard power connector with the PSU removed. Let's see if something easy jumps out at us.
 
Well the reading kept frifting up on the readions so these will probably be approxamate on the +5 furthest from +12 I get 3.304 on the second 2.783 the third 2.802 and on the one closest to +12 I got 4.00.
 
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