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Video card faulty?

I still don't hear a beep. What now?
So we need to determine if it's the motherboard that is faulty, or the power supply.

1. Do you have access to a multimeter and have knowledge of how to use it to measure DC voltages?

2. In the 'minimum' configuration, is the power supply cooling fan turning? Note that a turning fan does not alone indicate a functional power supply - we can use the information later.

3. Do you have a spare power supply?
 
First, confirm for me that only the motherboard is connected to the power supply. We don't want anything else (such as a drive) shorting out the power supply.

Will a modern Power Supply work?
Yes, if it has the required connectors that fit to a 5150 motherboard. Otherwise you would need to purchase adapters. If you have one with the required connectors, try it.
 
I just noticed that I THINK I may have heard the HDD spin up.
Will you tell me what I should do first?
 
We need to establish if 'minimum' configuration works or not. How we progress from there depends on the outcome. So speaker/motherboard/powersupply only - only the motherboard is to be connected to the power supply. With 'minimum' configuration, do you hear a beep approx. 50 seconds after power on?
 
Ok.
Is there a trick to removing power from the floppy disk? It is in such an akward spot...
We don't know if you have the original IBM floppy drive or whether it has been upgraded (e.g. to a half-height one).
In any case, sometimes connector removal can be facilitated by removing the screws that hold in the floppy drive, then moving the floppy drive an inch or so.
 
Ok. I tried minimum Configureation. No luck. However the HDD is spinning up. Could it be the 8088?
I'm confused. Minimum configuration does not include the HDD. Was the HDD connected or disconnected from the power supply in your minimum configuration test?

Could it be the 8088?
We haven't even yet determined if it is the motherboard at fault, let alone the 8088 chip on it.

One thing at a time. Just follow my instructions and answer my questions. We'll get there.
Was the HDD connected or disconnected from the power supply in your minimum configuration test?
 
Since we had a display beforehand, and since minimum configuration fails, we know now that what has failed is either the motherboard or the power supply.

POWER SUPPLY

It sounds like you have no other computers in which you can test the power supply, and no spare power supply. Let's do a basic check of the power supply.

The diagram at http://members.dodo.com.au/~slappanel555/misc/IBM_5150_PSU_pinout.jpg shows the pinout of the power supply.

You won't have the original IBM 63W power supply because it will have needed to have been upgraded to cater for the addition of the hard drive, but the pinout will be the same (with a possible exception that the "Key" pin in the diagram may have +5 volts on it).

The power supply will probably require an adequate load of some kind. The hard drive will do. It's a reasonable assumption that the hard drive isn't overloading the power supply because the odds of you having both the hard drive and the motherboard overloading the power supply is extremely low.

With only the hard drive connected to the power supply, what DC voltage is on the following pins:
* Pwr Good (should measure about +5 volts)
* +5 volts
* -5 volts
* +12 volts
* -12 volts

If those five pins measure as expected, with only the (good) HDD connected, then you can be very confident that your power supply is good.
 
POSSIBILITY 1 - FAULTY POWER SUPPLY

At some point you heard the spindle in the hard drive turning. That requires +12 volts. And so if the power supply is the faulty item, then it's because the power supply isn't generating one (or some) of the voltages. Or it's possible that the power supply is generating all of the voltages but not the 'power good' signal. It's not going to be a 'replace the fuse' scenario. Even if you open up the power supply and spot a damaged component, I doubt that you have the tools (e.g. soldering iron) and skills to replace the component.

The realistic situation would be that you would need to acquire a replacement power supply.

POSSIBILITY 2 - FAULTY MOTHERBOARD

If the motherboard is instead the problem, then you have a chance. Often, especially after the motherboard has been sitting unpowered for years, a tantulum capacitor on the motherboard will fail. It's possible that such a capacitor has gone short and if we can identify it, we get you to simply cut it off the board using wire cutters. That's the best case scenario if the motherboard is faulty.

But maybe a socketed chip, such as a RAM chip, has gone short circuit. We can help you identify such a socketed chip. If one is found, you find a replacement.

Beyond that, I repair 5150/5160/5170 motherboards, but I'm in Australia. There may be a member of these forums close to you who may be willing to look at the motherboard for you.
 
Before you ponder my previous post, consider this.

At this point, you haven't done the test to identify whether it's the motherboard or the power supply at fault. Before you do that test though, an option is to do a thorough visual inspection of the motherboard because you may actually spot the cause of the problem. If the cause is a shorted tantulum capacitor, there may be a visual indication, as shown in the first two tantulum capacitor photos at http://members.dodo.com.au/~slappanel555/failure.htm
 
Your best bet would be to post your location (Pacific NW covers a lot of territory) and see who with the necessary skills is close to you. Chances are that you'll find someone close by.
 
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