55" Philips Smart TV blinks 2 times

[anton74]

Hello,
I am trying to repair the 55" Philips Smart TV (model 55PFL6008K/12). The red led blinks twice.  With the power supply connected to the mainboard, I measured the +3.3V and +12V on the output connector of the PS board.  When the power supply is disconnected from the mainboard, the +3.3V is present while the +12V is absent.  I suppose it is normal since no standby signal was applied.  However, in the "hot" side of the PS board, I noticed the black, discolored diode D501 (please see attached). This diode is marked as "T2D 23".  When unsoldered and tested with a multimeter, the diode reads open in both directions.  The diode is connected across the primary of the SMPS transformer and to the drain output (pins 6, 7, and 8 ) of the U501 IC (FSB127H).  I did not find too much information about this diode.  I have read on some forums that it could be the TVS diode, while the datasheet of the FSB127H refers to the regular 1N4007 connected in the same manner.  For example: https://www.eevblog.com/forum/repair/trying-to-fix-broken-psu-in-a-philips-46pfl8008s12-tv/.  Other discussions about this (or similar) diode:
https://www.avforums.com/threads/philips-46pfl8007t-12-diode.2237949/
https://www.mikrocontroller.net/topic/465167
https://forums.futura-sciences.com/depannage/828713-identification-diode.html
It seems that nobody identified this diode.

So, I am not sure whether this diode is bad. So, I have the following questions:
1) what kind of diode it is and is it bad or good;
2) since I have measured both +3+3V and 12V, and despite the discoloration of the diode, the power supply is probably OK.  Then, the fault is probably on the mainboard.  I have read that the reflow of the main processor or replacement of the entire mainboard is required.  How can I check the mainboard?  I started to measure the voltages on different voltage regulators; however, there are about 10 different voltage regulators on the mainboard.  Any information would be appreciated.

Anton.

[anton74]

Well, it seems that I 've found an answer on my own question regarding the diode - it seems that this is a transient voltage suppressing (TVS) diode and a fast recovery diode (FRD) in one package; probably ST02-170. Here is a datasheet: https://www.tme.eu/Document/430c98e056b0292bfda740fe9659b265/ST02D-170.pdf
It should measure open in both directions, and a discoloration is not a problem.  So, the power supply is probably OK.  That means the mainboard is defected, most likely the main processor needs to be reballed.