Philips PSU (715G7350-P01-000-002S) No stand by light (0V)

[blablaro]

Hi all,

This is the source from a Philips TV 43PUH6101 that suddenly stopped.
I know it's the source since I have ~ 0 volts on outputs 12VA/16VA, 12V/16V, +3.5/+5V

For the latest weeks I've been trying to figure out the problem with this. I've ordered all kind of mosfets, a capacity meter and other things to try to figure out the issue with this PSU. My wife thinks I'm crazi but I want to repair it

Initially, when I started the testing with the multimeter on diode mode (220 V on):
- discovered that was Q9101 shorted (or I shorted it)
- R9109 blew out
- both replaced
- replaced main fuse: F9902

On the back:
- D9105 was shorted - replaced
- just replaced the 8 pin SMD: U8601 that I read that usually gets broken.

Tested different diodes, mosfets, everything seems to be fine. Nothing else seems smoked, blown.

On the cold side everything everywhere I test voltage 0 so I believe it's something on the hot side.

On the hot side, the big brown capacitors have 320V and measuring with the - on the capacitor I measure 320 on D(drains) of all the big mosfets (on the hot side).

If somebody can help / guide through on what to check next, please let me know (I have a multimeter and a capacity meter: bside esr02pro)

Thank you for reading and the possible help!
Adrian

[nomoresonys]

How bout a picture of the whole back as to see how everything is connected.

[blablaro]

Please see the attached.

[nomoresonys]

I assume you checked D8609.

[lotas]

When a MOSFET breaks down, it often takes diodes, zener diodes and PWM with it. Check and replace.

[nomoresonys]

Sometimes they can be tough to figure out, I'm seeing these powerboards for about 20 dollars on ebay etc. At that price what I would do is get a replacement, you want to match up the numbers on the white sticker on the powerboard.

[blablaro]

I assume you checked D8609.

-> Yes, yesterday I removed a side from the circuit to test it because of the 2 rezistors (22 and 47 ohms) connected to the same side I could read 069 or 070 (normal and reverse). With one side removed, looks good.

When a MOSFET breaks down, it often takes diodes, zener diodes and PWM with it. Check and replace.

-> Just checked now the diodes and the zener diodes -> these are fine.
-> Not sure how to check exactly U9101 which is 3S121 (but I can order this from Ali)

Sometimes they can be tough to figure out, I'm seeing these powerboards for about 20 dollars on ebay etc. At that price what I would do is get a replacement, you want to match up the numbers on the white sticker on the powerboard.

-> I think I will order a replacement too but I want to repair this psu too if possible

[blablaro]

When a MOSFET breaks down, it often takes diodes, zener diodes and PWM with it. Check and replace.

I started investigating U9101 (3S121) to see if it's working. According to specs: GND is pin 8, VCC pin 7, Pin 4 ST.
I checked and ST has 220v, VCC has 0 V. Tested the rezistance between 7 and 8 and I have 80 ohm which I believe it's not good (according to chatgpt ) ).
C9113 seems fine. ZD9104, ZD 9105 seems fine. But between pin 8 (gnd) and pin 7 I see a small capacitor (C9139) that on diode mode show 80 (on both directions), could that influence or the main U9101 is bad? Should I check anything else here?
(attached a closer image from that place)

[lotas]

Pin 7 is VCC, and this pin shouldn't have 80 ohms relative to GND. Most likely, the PWM is faulty. Carefully remove one pin, 7 or 8, and check the resistance again.

It will be easier to unsolder the low-ohm resistor and check the resistance between pins 7 and 8.

And also check this resistor, I don’t like the look of it, the resistance in the photo, if 100, then the multimeter should show 10 Ohm.

[lotas]

Can't check?

[blablaro]

Can't check?

The indicated resistor R9111 (10ohm) seems to be open - 1 /OL, the one on top R9113 (82ohm) same / open. Good catch!
-> Just ordered them from Aliexpress and also ordered 3S121 (just in case and since it's cheap).

The low ohm resistor (R9155) is ok, I'll remove it tomorrow from the circuit and try again between pin 7 and 8. I'll keep you posted. Thank you!

[lotas]

If the resistors are open, then 3S121 is 100% not working, it has burned out.

[blablaro]

If the resistors are open, then 3S121 is 100% not working, it has burned out.

Thank you for you help until now. In this case I will test when I receive the resistors and the new 3s121 (around 10 days). I will keep you posted.