First post, by Raov
Hi everyone,
I found a LS-486E rev.F in my storage yesterday, and got to work seeing if I can make something boot on it. From what I've read it would be a great match for the CPUs I have (two IBM/Cyrix 5x86 100MHz and an AM486DX4-100), that is if it worked. I had two of those boards, one completely dead and another with either a dead keyboard controller or a skill issue on my side. I threw out the seemingly bad one a long time ago, and seems like I mixed them up.
The board on my hands acts almost as if there is no CPU installed at all - all voltages are present, along with ISA CLK and FRAMEs and a reset pulse on startup, but no POST codes (--). Same thing happens without the CPU installed, so I'm guessing at least the board's vitals are working.
What I tried:
-A visual lookover, all good
-Swapping CPUs
-Multiple jumper configs for each CPU tried
-Checking PSU against known working boards, works
After doing the above I decided to dig deeper and checked the CPU voltage regulator - 5v on the emitter, as it should be, base is 1.27v regardless of CPU voltage jumper settings, but the collector voltage behaves weird - starts out at 0.85v, then creeps up to 1.15v or so. When I bridge W1, collector voltage is 5v flat, base is unchanged. I have a suspicion that the transistor is shot, and would like to get a second opinion on this.
And of course, board pics.
