LG RZ-37LZ31, no power, faulty KNP-3370 PSU

[Chungalin]

Hi,

I have a LG RZ-27LZ31 LCD TV that doesn't power on. The 5V Stby are OK, but when you try to switch on, a relay clicks on the PSU several times but no other voltage comes from the PSU (5V, 12V, 18V, 24V).

I've tried the PSU alone, making a bridge between the 5Vstby and the DPM line. Same results, so it's not a short in any other TV part.

The PSU is a KN Powertek KNP-3370. The TV service manual doesn't include schematics from this board and I haven't found any.

Any ideas? Which is the primary switching controller or regulator that I have to check first? I don't detect any shorts in switching mosfets, as far as I can check.

[mscserbia]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

Post some pictures of that power supply.

[Chungalin]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

Not very good pics, but enough to start pointing zones to focus.

[budm]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

Can you list the labels of all the pins on those two white connectors? I would like to know what the 'DPM' pin is.

[Chungalin]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

One:

18V
18V
GND
GND
12V
12V
ACD
GND
5Vst
DPM
5V
5V
5V
GND
GND


The other:

24V
24V
24V
24V
24V
GND
GND
GND
GND
GND
12V
12V
GND
33V

Only 5Vst is present when powering the board.

[budm]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

OK, I have no idea what 'DPM' stands for.
But the bottom line is that the main board is not sending any signals back to the power supply board.
When you bridge the 5VST and the DPM line, did you remove the DPM wire going back to the main board first?

[Chungalin]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

I'm trying the PSU alone on the desk, completely isolated from the TV. Unless the PSU has some kind of undercurrent protection, it's supposed that all those voltages have to show up once it's fixed...

[budm]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

We need to find out what that DPM line goes to on the board. By the way, did you see the DPM goes HIGH when TV is turned on and goes LO when turned off? If it is control line then it should toggle LO-HI, HI-LO with power switch.
Need to find SCH of this board or a working board to do comparison readings.

[Chungalin]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

Service manual available at ElectroTanya. Schematic of power connector at page 44. As you say, I noticed that when the TV wanted to turn on, DPM line went to 5V. Could not find what does ACD, schematics aren’t searchable. Thre’re no other control lines.

[budm]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

'ACD' is AC Detect (same as AC OK in some other brand)

[sordids999]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

Hi Chungalin

did you ever fix this problem i have the same fault im trying to fix for a family member

[Chungalin]

Re: LG RZ-37LZ31, no power, faulty KNP-3370 PSU

Sorry Sordids, I forgot to suscribe to this thread and didn’t see your question. I never managed to repair this and now I’m salvaging boards from this TV and discard the remaining parts.