I have a similar problem, had it discussed with you by email but i think you did not received my last one where you have a link with a video to see what the clock shows. So, the problem is: Somehow i shorted something, a metal object was on the table during the soldering and shorted 2 pins under the PCB, i do not know which of them, just heard the buzz sound.
The clock enters TEST mode, shows 00:00:00, 11:11:11, 22:22:22, etc and when i press the switch at 88:88:88, it enters in calibration, shows random digits and then shows 01:96:00, after that 88:88:88 and then goes black, shuts off the tubes, backlight leds and tick leds but the led on the PCB is on.
I am thinking to get out the PCB all the pieces and rebuild the clock, i bought all the parts apart of micro controller and make tests at each step....i do not have any idea...
I took out the microcontroller and installed it on my clock and it works just fine...do not get it
Here's a thought... see if maybe it applies to your situation...
The point in the sequence when your clock blacks out is, I believe, the point where LDR dimming first becomes enabled. LDR dimming is disabled during TEST. Even if you have no LDR connected I'd say to take a good look at all parts & traces associated with the LDR.
With no LDR connected you should see 5V on Pin 24 of the controller (because of the 10K pull-up resistor - R11 on Classic boards, R17 on All-In_one boards)
If you have a WiFi module installed and working, try connecting via WiFi and turning off LDR dimming.
I could be totally off base with this idea but it is sure interesting that the clock blacks out at that particular point.
Look into it later when the dust is clearing off the crater.