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486 motherboard no life

E-monster550r

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Joined
Sep 26, 2022
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I have a generic 486 board. It has an intel DX2 processor and runs Amibios by American Megatrends. All I have is fans running, no beeps, no video. The board gets slightly warm, but thats it. I removed the chips, found a bent pin on the bios chip. I reinstalled the chips and tried again, same result. Any thoughts?93F4CF46-FC04-4938-95E5-E9BFF4C9629A.jpeg58620AFD-D514-41DD-9E6F-A05BA7F5531A.jpegEBAA013D-D7C2-4FD5-AE3D-3C331657A600.jpeg
 
Your photo doesn't show any RAM installed. Did you have some (compatible) sticks in when trying to boot?
 
I had an issue where the keyboard fuse was bad. When I jumped the fuse link the board came to life. It was also a 486 VLB board similar to yours. I didn't replace the fuse yet. I just have to remember to plug the keyboard in with the power off.

Seaken
 
Where is the keyboard fuse?
Some motherboards do not have them. They are normally close to the motherboard's keyboard connector. For example, in the photo at [here], you can see the word "FUSE" up near the keyboard connector. Often, it will be labelled as "F1".

However, I was surprised reading Seaken's experience. The fuse protects the motherboard in case a problem in the keyboard overloads the motherboard's +5V line. If the fuse blows, normally it just results in no +5V going to the keyboard. It is just like having no keyboard attached, and one sees an on-screen message like 'Keyboard error'.

Your photo doesn't show any RAM installed. Did you have some (compatible) sticks in when trying to boot?
I have all the ram and chips removed.
For some motherboards (specifically the fitted BIOS), if bank 0 is missing or is bad in some way, there will be no on-screen display at all.
Although, for an AT-class computer, one would expect error beeps (but there is no guarantee).
Do you have a POST card?

The ram came with the board.
The RAM chips in the first photo of post #1 look like cache RAM, not 'normal' RAM. That will be why T-R-A used "sticks".
 
So with everything fitted, "All I have is fans running, no beeps, no video."

* You do not know what the previous owner has done. Verify that the RAM sticks are valid for the motherboard, and are in bank 0.
* You do not know what the previous owner has done. Verify that jumpers are in the correct position.
* Does a POST card reveal anything?
* Does the Supersoft diagnostic ROM show anything?

I have a generic 486 board.
It looks like a variation of the HOT-419.
 
Hi could you also confirm that the power supply is working? What I mean by working, is that it appears to be delivering the correct voltage levels with a power good. It might be good to install the parts into the board and take a picture of your test setup.

Per your description of a bent BIOS chip pin, you might want to inspect the socket that it is making proper contact with the BIOS chip pins, and to the motherboard. I've seen it happen before that these sockets fail to work when the leads are in bad shape.
 
Do you have an Eeprom programmer? I would start with making a new bios chip, and clean the ram sockets really good with some deoxit (WD40 electronics contact cleaner and lube works well too, Quick dry electronics cleaner by CRC works ok in a pinch). Throw a little on the cpu socket as well. Also clean the fingers on the ram if you see anything that looks dull. Pencil eraser and rubbing alcohol work for that usually... Common issues on Pentium and earlier motherboards.

When the motherboard is on, does the voltage regulator next to the cpu socket get warm?
 
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