Re: LG 42LE4500 - No 20V rail

Pin 7 is 1.87-1.9V and pin 8 is 0V. So it looks like the inputs to IC101 are good.

I also desoldered one of the transformers to check the coil arrangements and make sure there weren't any shorts/breaks. It all checked out and the bottom two pins on the secondary side are a single coil, so not seeing anything on the scope on these pins would indicate no/bad input to the primary coil.

So do you think it would be best to swap out IC101 and possibly the MOSFETs on the primary side?

Re: LG 42LE4500 - No 20V rail

Between the VCC pin (#12) and GND (#10) on IC101 I'm reading 13Vdc.

Re: LG 42LE4500 - No 20V rail

IC101 is an ST L6599 Resonant Controller, datasheet here: [url]https://cdn.badcaps-static.com/pdfs/f0c5cb6fa2fff728c840527cd0b455f4.pdf[/url]Re: LG 42LE4500 - No 20V rail<br /> ...55f4.pdf[/url]

Re: LG 42LE4500 - No 20V rail

Ok I'm reading 393VDC on that fuse.

I have the service manual for the 42LE4500 with schematics for the main board - unfortunately not the PSU.

#18 DRV On - goes to the INV_CTL pin on the MICOM
#22 PWM DIM - goes to the LVDS and PWM2 on the MStar CPU
#20 SCLK & #23 SIN - according to the schematic and option resistors on the board these pins are N/C
#24 Error Out - I'm not sure on this either, all I know is that it's an output from the LED driver daughterboard on the PSU

The only thing...

Re: LG 42LE4500 - No 20V rail



Thanks, I clearly need to learn more on this so I'll do some research before trying anything with the scope. I take it if I'm using a battery powered multimeter I can take primary side readings between the point I'm checking and the negative main filter cap leg without any issues?



All these readings are taken when the set is 'on':
#1 Power On: 3.41V
#2/3/4 20V: 0.02V
#5/6/7/8 GND: 0V
#9/10/11/12 3.5V: 3.51V
#13/14/15 GND: 0V
#16 V-sync: 0V
#17/19/21 12V:...

Re: LG 42LE4500 - No 20V rail

I attached the probes to both Q102 and Q103 S pins and the result looks very similar to the input to the transformer (see attached). Voltage doesn't go much above 0, but goes as low as -50V.

From what I gathered from IC101s datasheet Q102 and Q103 should be alternating, but they're in perfect step....

Re: LG 42LE4500 - No 20V rail

I'm checking for 20Vdc on the output of the rectifier on the cold side (getting 0Vdc), and I'm looking for 20Vac on the inputs of the rectifier which are connected directly to the output of the transformer (getting 0Vac), but I've also measured from the pins of the transformer directly to be sure.

I'm wondering if I'm not doing the measurement correctly because I'm so used to DC. I'm connecting the reference wire of my probe to the chassis ground - which I've checked is connected to the GND pins on P201. But that's DC, do I need a different...

I'm trying to fix an LG 42LE4500-ZA TV for a friend, and I was hoping someone might be able to help. At first glance it looked like the backlight had gone, but on further investigation it turns out the 20V power output from the PSU isn't working.

The PSU has the Model: YP42LPBA, Part Number: EAY60803202

The 3.5V output is working, so the MICOM on the main board powers up and will attempt to power on the TV when the power button is pressed. Power On will go high, the front panel LEDs will do their power on dance and the relay will click on, but there's 0V on the 20V...

Re: New Members - please post your introductions here

Hi, I'm a software engineer by day but by night I love tinkering with hardware and reverse engineering stuff. I've done a fair bit of electronics, but I haven't studied it properly, so I have some rather large gaps in my knowledge.

I'm here to fix things, but most importantly learn how to.