I have two of those "Techmedia" 486 motherboards that have the onboard 5428 VLB SVGA, and onboard UM8672 VLB IDE.

One of them is working great.

On the other, it isn't stable, because it keeps resetting and rebooting by itself.

At first, with a RAM and CPU outfitted, I noticed that when first applying power, the LED display on a POST card goes haywire, cycling through the first set of codes very quickly, then the system stabilizes a bit. It stays up and running long enough to enter SETUP and save some settings, sometimes even long enough to boot into an OS, but never more than a few minutes without rebooting.

Next, I noticed that even with no RAM, no CPU, and no BIOS chip, it still keeps resetting by itself. Monitoring the RESET DRV on an ISA slot with an oscilloscope, it would sometimes reset multiple times within a window of a few tens of milliseconds. Finally, I noticed that in this state, but with the POST card, if I apply power and move away, the RESET light on the card stays on solid. As I move my hands closer to the board, the closer I get, the faster the RESET LED blinks, indicating going into and out of reset at a faster rate.

There was light damage on this one around the removed NiCd battery. I have touched up some of the corroded traces with extra solder, but there was only one corroded enough to lose continuity. I added a bodge wire to that one and it still makes no difference.

Does this sound like more battery damage I've missed, or some internal failure inside the UM8498 chipset? It was an interesting story to tell, anyway.