Greetings,

So I bought this TC430HX as a new old stock (supposedly), there was box and all components present, but it was not sealed. The board itself did looked like new. To test the board at the time I was missing RAM, so I ordered a pair then assembled everything on a test bench and it did not POST. Eventually I blamed it onto a "wrong" RAM, because I knew that other components were working. So I bought a new RAM, also better CPU (MMX 233) and even S3Virge video card. Then again I assembled everything and it did not POST. Mobo originally did not have a pc speaker, so I soldered one in, still no sound nothing. Tried different configurations with jumpers, did not help. Bought a POST diagnostics card, it showed that the voltage is supplied but no codes, nothing starts, does not POST. At that point I realized that it could very well be a PSU issue, I was using modern PSU for testing and maybe missing -5V rail is the cause. So I switched to old Enermax PSU and vuala it started beeping and posting and I got output on my screen (good that I made some photos of that). I thought the enigma is solved, so I assembled the PC into a case with all the components. Turned it on and it did not work... So I removed all the components again, put it back on the test bench and now it does not POST again. And since then I did not manage to make it start. Recently I even replaced voltage regulator, because it seemed to run hot, but it did nothing. Those couple SMD electrolytics gives a good ESR reading, so it's not caps. There are no visible damage of any kind, cracked joints etc. It seems to me that it is the reason it was NOS in the first place, because it was always like that...

One interesting thing I noticed when mobo was installed into the case. Instead of steady light, the power led was actually blinking. As if PC was in sleep mode. Here is stuff I found in documentation:

1.10.12.3 Sleep LED This header can be connected to an LED to provide a visual indicator for when the system power is turned on […]
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1.10.12.3 Sleep LED
This header can be connected to an LED to provide a visual indicator for when the system power is
turned on or when the system is in sleep mode. When the system is powered on, the LED will be
continuously lit. When the system is in sleep mode, the LED will blink at 1 Hz.

1.10.12.6 Sleep/Resume
When Advanced Power Management (APM) is activated in the BIOS and the Operating System’s
APM driver is loaded, Sleep mode (Stand-By) can be entered in one of three ways: an optional
front panel “Sleep/Resume” button, a user defined keyboard hot key, or prolonged inactivity. The
Sleep/Resume button is supported by a 2-pin header located on the front panel I/O connector.
Closing the “Sleep” switch will generate an SMI (System Management Interrupt) to the processor
which immediately goes into System Management Mode (SMM), the so called “Sleep” mode.
The front panel “Sleep mode” switch must be a momentary two pin SPST type that is normally
open. The function of the Sleep/Resume button can also be achieved via a keyboard hot-key
sequence, or by a time-out of the inactivity timer. Both the keyboard hot-key and the inactivity
timer are programmable in the BIOS Setup (timer is set to 10 minutes by default). To re-activate
the computer, or “Resume”, the user must press the sleep/resume button again, or use the keyboard
or mouse. Mouse activity will only “wake up” the computer if a mouse driver is loaded. While the
computer is in Stand-By or “sleep” mode it is fully capable of responding to and servicing external
interrupts (such as an incoming fax) even though the monitor will only turn on if a user interrupt
(keyboard/mouse) occurs as mentioned above

Trying momentary switch on sleep pins did nothing. But for example with diagnostic card I see that reset switch does work. So it looks as if system is in some kind of permanent sleep mode.

I'm pretty much out of ideas on what to do next. Mobo looks good and it's a shame to scrap it.