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View Full Version : Repairing a dead 286 motherboard



Anonymous Coward
September 25th, 2008, 07:29 PM
I recently got around to testing a 286 motherboard I received in a lot of hardware I bought. I was pretty excited as it was a 0ws 12MHz model (the sweet spot for 286s). However, I am not able to get any kind of response out of it. Nothing on the screen and no beeps. I tried replacing everything in a socket and I scanned and tested the board for cut traces. What might cause something like this?

Here is my board:

http://artofhacking.com/th99/m/U-Z/30521.htm

Unknown_K
September 25th, 2008, 08:53 PM
Any battery leakage?

Chuck(G)
September 25th, 2008, 09:43 PM
This is the point where I'd get my scope out and check for clock signals and see if the reset line is behaving itself. Some of these old boards required the "Power Good" signal on the power supply connector; others didn't--so you may want to check that your PSU is supplying it.

Does the PSU fan keep running when you turn it on? If not, you've likely got a short somewhere on the mobo.

Try swapping the crystal for a known good one.

After that, I'd hang my scope on the address lines on the expansion slots and see if the machine is flatlining.

If not, check the position of the BIOS EPROMS--make sure that they're not swapped; make sure that the mobo EPROM jumper JP1 matches what you've got. If you've got an EPROM programmer, take a look at the EPROMs and make sure they're okay.

BIOSes don't usually require any RAM to sqeak out an error beep, so you might remove all of the RAM chips to make sure that they're not jamming a signal.

Check the expansion connectors carefully to make sure that the contacts look okay--I've seen mobos where contacts have been shorted against one another by some gorilla jamming something into a slot the wrong way.

Turn the board upside down and tap on it to see if anything falls out.



This is one of the reasons that I hate playing with the newer 286 and 386 mobos--if the support chipset is toast, there's not much you can do. I like the ones where all of the mobo is pretty much all known LSTTL commodity parts.

Druid6900
September 26th, 2008, 11:21 AM
I recently got around to testing a 286 motherboard I received in a lot of hardware I bought. I was pretty excited as it was a 0ws 12MHz model (the sweet spot for 286s). However, I am not able to get any kind of response out of it. Nothing on the screen and no beeps. I tried replacing everything in a socket and I scanned and tested the board for cut traces. What might cause something like this?

Here is my board:

http://artofhacking.com/th99/m/U-Z/30521.htm

If you don't already have one, go on fleabay, find an inexpensive PCI/ISA P.O.S.T. card and buy it. They come with manuals to decode the hex error code displayed for a number of different (and old) BIOSes and it will be the best 15 to 20 bucks you ever spent.

Denis
October 1st, 2008, 09:22 AM
Something else to check, do you have a F82C206 chip on the board? Usually manufactured by Chips and Technology? It's the DMA controller and was notorious for failure on boards from that era.

whansen02
October 1st, 2008, 03:00 PM
i'm just getting into this end of computers myself & in doing so it amazes me how far technology has come & fast. sure is going to be cool to see where it takes us from here. it blows my mind when the 286 is refered to as being from an era. i love it. i'm not going quite that far back to start, but i'm planning to work my way back as far as i can.
right on fellow geeks. cheers

Anonymous Coward
October 2nd, 2008, 06:21 AM
This board uses a VLSI chipset. However, I suspect you are right...it's probably a bad IC.

channelmaniac
October 9th, 2008, 08:56 PM
One of the early things to do in POST is to initialize the scratchpad RAM which is the lowest 64K in the memory space. Try swapping out the lowest bank of RAM and see if it will come up enough to beep as some systems will beep if the scratchpad is bad or missing, others will just hang.

Another thing to check is the keyboard fuse and the keyboard controller "BIOS" IC. It's not really a BIOS, but a microcontroller. If it fails the system will act dead too.

RJ