No post at all -> check BIOS ROM first, also check for shorts on the voltage lines. If there is a short, replace all tantalum caps. Also check the voltage regulators.

If all that is ok, install a diag card that shows the post code and look up what the code means.

2) How to check for power on okay ?

3) How to check if CPU is okay.

You don't check that. If you want to check & repair a broken mainboard, you *must* use a known-good CPU and PSU.

How can I tell if power-on is working okay ?

I have never repaired a motherboard before, So I am a Novice and am asking for advice on how to go about it.
What I mean about CPU, is how would you check if CPU socket is okay and working properly ?

The tools I have are a meter for checking voltage and microfarad ( µF ).
flux, solder and soldering iron.

I would say don't replace all Tantalum caps even if one of them have failed, just replace the failed one.

If you keep using the motherboard after you get it working the non failed tantalum caps will likely continue to work "for ever" as they don't generally get worse with age as long as they are used frequently.

Tantalum caps tend to blow, short out or just fail "open" after the item in question hasn't been used for a very long time, especially if it has been stored in a humid enviroment like a basement. The caps have a hard time handling the sudden rush of current after beeing idle for many years.

But as already has been mentioned the BIOS is just as likely to be the issue as a failed cap. If the (known to be good) PSU fail to even start it's pretty much always a short(ed cap) on the motherboard though.

How would I check the bios ?
Is it just a matter of re-seating the bios chip ?

I would say don't replace all Tantalum caps even if one of them have failed, just replace the failed one.

Well, often you don't see which one has failed and you have to desolder them for testing. But then you can just replace them all.

How can I tell if power-on is working okay ?

I'm not sure what you actually mean with "power-on". This is an AT mainboard. There's no power-on logic on the mainboard as with ATX. So if the PSU is working, there's power supplied to all components.

How would I check the bios ?

Either by putting it into a similar mainboard and see if it comes up, or by reading out its contents using a programming device.

So I guess I will start by checking all the caps with a microfarad meter.

Intel486dx33 wrote:

So I guess I will start by checking all the caps with a microfarad meter.

Just making sure you read derSammler's post: You can't measure the capacitors while they're still on the board. You'll have to desolder them first.
Why not start with the obvious things? If there's any capacitor leakage neutralize/clean/replace and check continuity of affected tracks. Check for missing chips. Check jumpers configuration. Find known-good PSU+cheap vga+memory and fire the thing up. Connect a speaker and listen for beeps. Are there any? Is the CPU getting warm? Do you have another working machine to check individual chips?

derSammler wrote:

Well, often you don't see which one has failed and you have to desolder them for testing. But then you can just replace them all.

I usually first check if either the 5V or 12V rail is shorted to ground right at the AT power headers using the low resistance range on the multimeter. If I find a short I poke around with the multimeter measuring the resistance over every suspect cap until I find the shorted one, this can be done with all caps in circuit.

Mostly tantalum caps short and blow up like fire crackers and then it's easy to see which one has failed or short but stay intact and then you can poke around with the multimeter using the low resistance range until you find the shorted one.

Perhaps it's best to mention that this should be done with the power supply disconnected from the motherboard...

With tantalum caps measuring ESR, capacitance and break down voltage is rarly needed. Tantalum caps are in my experience either good or bad, working or not working.

Intel486DX33, does the PSU engage, or go into short circuit protection mode? In the past, when my PSU was going into short circuit protection mode, it was because a tantalum capacitor shorted itself out. Taking a multi-meter around to all the through hole capacitors to check for a short quickly revealed which capacitor was faulty. I replaced the one capacitor and was good to go. There was a thread on this, AMI Mark V Baby Screamer 386 dies spontaneously

I also have a lengthy thread about fixing a dead 386 motherboard. You might want to review this thread for some ideas, https://www.eevblog.com/forum/repair/how-to-t … tvp7f0g11lpbpv6

Thanks everyone for your help.
I think I have an Idea as to what to look for and where to start trouble shooting.