LG 50PG3000 Plasma - No Display

[greglogan]

Hi guys

I'm having issues once more. This time with the set mentioned above. There is no display at all but I do have audio.

All fuses have been checked and are showing continuity as good
All Va and Vs voltages have been checked.
I replaced a couple of very unhappy caps on the PS board and the main Y board.
I have removed the Y buffer boards one at a time and no result. Also, when the boards were out, I checked for continuity between the ground connector and all the pins. No continuity showing, so all looks ok there.

Am I looking at a bad panel or is there any other checks I can try? The Z-sus board mentions very high voltages at the connectors but I am getting next to no voltage showing there at all - just a couple of volts.

Any help greatly appreciated!

thanks

greg.

[Biruslapio]

Re: LG 50PG3000 Plasma - No Display

To check for shorts on the Y-Buffer output pins, you used the floating ground, correct? Not the chassi ground pads, because that has capacitors in series and it will always measure open.

Does it have -VY, VSCAN/VSC/VSCN and Z-BIAS/VZB matching the panel specs (panel sticker on the top region)? the logic board also has to have a green led blinking or always on at least.

To remove more variables from the test I recommend to unplug main board even if you have sound, short the EXT_AUTO_GEN pins on the logic board and unplug the LVDS from main.

[greglogan]

Re: LG 50PG3000 Plasma - No Display

Hi
Yes, meant the floating ground. The boards were out of circuit when tested.
The logic board has a green LED, I think it varies from blinking to static. Not sure how to check for -VY, VSCAN or VZB......but happy to try if you can point me in the right direction.

I'll give the main board a try in the morning. Should I disconnect all cables on the main board or just the LVDS?

thanks

Greg.

[R_J]

Re: LG 50PG3000 Plasma - No Display

Have you checked the fuse on the Z-sus board? Post some pictures of the back of the tv and the boards so we can see what we are dealing with.
Have you checked the other threads on this model?

[Biruslapio]

Re: LG 50PG3000 Plasma - No Display

Remove the main board power cable and LVDS, the power supply turns itself on when no main board is present.

What part number is your Y-SUS and Z-SUS? Need the EAX or EBR code to find out exactly which boards you have because I've found multiple different PCBs online, then I can point out where the VSCN -VY and VZB test points are.

[greglogan]

Re: LG 50PG3000 Plasma - No Display

Hi R_J

yeah, I've had a look at the other threads. Most with similar faults seem to point to the buffer boards. Yes, all fuses have been checked and are good.
Pics to follow in a bit

[greglogan]

Re: LG 50PG3000 Plasma - No Display

Hi Biruslapio
part nos as follows:
Y-SUS EAX39647101
Z-SUS EAX39648501

thanks

Greg

[greglogan]

Re: LG 50PG3000 Plasma - No Display

In order to short out EXT_AUTO_GEN, should I solder in some headers or just bridge with solder and a piece of wire?

[Biruslapio]

Re: LG 50PG3000 Plasma - No Display

Highlighted are resistors for measuring VSCN (47kOHMs top) and -VY (100kOHMs top) and some others that fail when IGBTs short, they should not measure open or more than they're rated for.
VZB you measure from that resistor + to chassi ground.

I always solder a flexible small wire between the AUTO_GEN pads shaped like a U, to ensure there's no problem with poor contact.

Should also add, I've had one of these TVs with a defective top buffer, none of the output pads were shorted, but some SMD capacitors in parallel with the ICs were measuring 40 OHMs, and the Y-SUS VS fuse was open, nothing else damaged, replaced the fuse but the TV actually worked with half the lower screen, so a bit different than your fault.

[greglogan]

Re: LG 50PG3000 Plasma - No Display

Hi

thanks for the info. The z-sus board looks fine, however y-sus board appears unhappy. There is less than 0.5V showing on both VSC and VY. So, you're certainly getting me in the right direction it would appear. Some of the resistors are showing different values than their banding but I'm guessing that is because they are still in circuit? None are showing open or dead short.

Further checks ongoing but I'm open to any suggestions

[Biruslapio]

Re: LG 50PG3000 Plasma - No Display

On the Y-SUS board there are 2.2, 1.0 and 10 OHMs resistors circled, some 2.2 are in parallel, so should be 1.1 or less. I forgot to circle one below VR502, a red vertical one

If the resistors are good or bad, and the VS fuse on Y-SUS is good, you need to remove the board from the TV and check every IGBT and MOSFET in the heatsinks. Anything below 300 OHMs between C-E/S-D is a bad sign.

[greglogan]

Re: LG 50PG3000 Plasma - No Display

apologies for the massive edit. I checked both VR502 and R513 with my LCR tester. Approx 1.34 ohm which I suspect is within range.

Or am I going nuts?? Should these be 10.4K? Any help greatly appreciated!

many thanks

Greg.

[Biruslapio]

Re: LG 50PG3000 Plasma - No Display

I couldn't see the exact value because the on the photo they're vertical, the reading seems normal, they have 5 bands which confuse which way they're supposed to be read.

[greglogan]

Re: LG 50PG3000 Plasma - No Display

I think they're Brown / Black / Gold / Red

or possibly...Black / Red / Gold / Black but that doesnt seem to work either

The fact they're both reading roughly the same on the LCR tester makes me think they're ok

[greglogan]

Re: LG 50PG3000 Plasma - No Display

Looks like I'm gonna have to retire this one. It appears to be beyond my diagnostic skills

Thanks for all the help guys!