LG 42PC1D plasma - clicking repeatedly

[tom66]

Got this for cheap. I initially thought it was a bad hybrid, but then I noticed the power board had 7(!) bad capacitors on it. 6 of them are 3300u/10V Samwha WB and one is a 680u/50V Samwha WB. I replaced 4 Samwha WB in my 42" LG LCD I got from the dump - so the WB series seems very problematic.

Upon plugging in, the inrush limit relays click, the screen briefly flickers white, then a whining sound is heard, the relays click back and the TV switches off. The cycle repeats about once every 2 seconds. Interestingly, the status LEDs on the control board fade out when the relays click back - they don't go off abruptly.

Using my Atlas ESR60, all the bulged caps test bad (>0.03ohm ESR for most.) One, which was not that badly bulged measures 1.51ohm ESR!! So very clearly failed. I tested the other caps on the board that weren't bulged, and they seemed okay.

To verify it was not either sustain at fault, I disconnected both Y and Z sustains and the TV continued clicking, except this time the screen remained completely dark which I expected.

As the plasma panel lights up (quite brightly too, if only for half a second), I assume it still has its gases, and the hybrids are good. I will check the fuses later on the sustains. And I'll try and post pictures later - currently battling with the SD card reader. Ugh.

To PlainBill, master of LG, how much experience do you have with this particular TV? Have you encountered this issue before?

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Found the cable.......

[PlainBill]

Re: LG 42PC1D plasma - clicking repeatedly

I've never had that issue. It does seem to use the same panel as the 42PC3D-xx TVs.

PlainBill

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Caps ordered. Used Chemicon KZE 3300u/16V for the Samwha WB 3300u/10V (difficult to find a low ESR 10V one, at least at a decent price), and Nichicon HE 680u/50V for the Samwha 680u/50V. Will post back if it works.

I tried replacing the really badly failed 3300u (which measured 1.5 ohms ESR) with a Panasonic FC 4700u/6.3V, but no dice, still clicking. The 4700u isn't part of the main outputs - it's a 3.3V step down buck converter - so I figured it might be okay with 4700u (and 6.3V, because it's a 3.3V rail.) I'm guessing the other caps are destablising the power supply in some way.

[PlainBill]

Re: LG 42PC1D plasma - clicking repeatedly

Caps ordered. Used Chemicon KZE 3300u/16V for the Samwha WB 3300u/10V (difficult to find a low ESR 10V one, at least at a decent price), and Nichicon HE 680u/50V for the Samwha 680u/50V. Will post back if it works.

I tried replacing the really badly failed 3300u (which measured 1.5 ohms ESR) with a Panasonic FC 4700u/6.3V, but no dice, still clicking. The 4700u isn't part of the main outputs - it's a 3.3V step down buck converter - so I figured it might be okay with 4700u (and 6.3V, because it's a 3.3V rail.) I'm guessing the other caps are destablising the power supply in some way.

And I have had a consistent record in repairing these supplies - 0%

PlainBill

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

And I have had a consistent record in repairing these supplies - 0%

PlainBill

It's worth a shot.

I've noticed the newer 42PC1D etc. PSUs use Samyoung capacitors in the same place as the Samwha ones which have failed. The WB series is extremely problematic and fails in Samsung and LG TVs. I've found XC to be problematic, too. (Samyoung is related to Chemicon, so I'd expect them to have a higher reliability than Samwha do.)

I did do a test of the rails, and found them to be okay initially, but when the display lights up, they rapidly collapse - I'm not sure what conclusion to draw from this. The sustain voltages rise quickly to within 0.5V of their rating when the display flashes but collapse quickly when the display goes off. Also, when the display lights up, it's random garbage pixels, although "mostly" white, there are a few red/green/blue pixels, and it changes every time.

I tried disconnecting the control connector. The inrush relay then clicks every half second, the display flashes at the same rate, but nothing much more happens.

Manufacture date is January 2007, but the people I bought it off said it's already had a new "part" installed by a technician, and failed only a year later after that, but they didn't say (nor did I ask) if the problem was the same as I've currently got.

Worst case, found out the remote control is compatible with my LG LCD I got from the dump.

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

I replaced the bad caps, unfortunately it's still dead - stuck clicking away. Going to get out the meter and test everything.

Replaced all the 3300u/10V and one 680u/50V. Didn't replace a 680u/63V (not bulging); maybe I should? None of the Vs or Va caps were replaced as they rarely fail.

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

I replaced all the 3300u and then I read somewhere that replacing the 1000u would be a good idea. I tested it and it measured 0.33 ohm ESR!! However, even after replacing it, still not working...

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Does anyone have any suggestions?

I've now replaced the main board and AV board.

I've noticed the RELAY_ON appears to switch on/off with the relay clicking, so I'm suspecting the power supply is not working well and the main board is telling it to turn off, but why? The voltages are okay. The only thing a little suspect is the output ripple, which looks to be around 200mVp-p... I will re-test this later.

All but a few of the capacitors have been replaced but the ones that were not replaced were checked for ESR and found to be okay.

I think I need to get it on my bench and probe some things with the isolation transformer + scope.

Right now it's not really worth me replacing any more boards or major components, so it might go for spares. Shame, looks like a nice TV.

[bbjunkie]

Re: LG 42PC1D plasma - clicking repeatedly

Keep me in mind for the y-sus and buffers

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Keep me in mind for the y-sus and buffers

You can have the Y-sustain, buffer board and Z-sustain for a decent price, if you like... that's if (or when) I give up on it in a week's time.

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Okay, so I tested the PSU ripple on 5V (main.

It's HUGE!

About 1Vp-p at a few hundred hertz.

I measured high ripple before, but not this high - at least I didn't think it was that high. It's surpassing one division at 50mV/div (on 10X.)

So, then I unplugged the main board connectors. The relays twitched a few times, and the 5V rail came up - with no ripple. So, does this mean my second hand board is bad? Maybe something on it is shorted?

The next test is to load the 5V rail. I've got a 3.3R 25W resistor, or I can use several 10R 3W resistors (got 10.)

I think I need to get Big Bertha out - my 100 MHz digitising scope. Not easy to carry, but would be better for debugging the secondary.

[pecrie]

Re: LG 42PC1D plasma - clicking repeatedly

> I've now replaced the main board and AV board. <

Hi Tom66 ,

Just a question ,what do you mean with the AV board.Is it ,what they also call ,the LVD board ,or the Control board??

Well ,I hope you can get it to work.

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

> I've now replaced the main board and AV board. <

Hi Tom66 ,

Just a question ,what do you mean with the AV board.Is it ,what they also call ,the LVD board ,or the Control board??

Well ,I hope you can get it to work.

The AV board is the one with the SCART and analogue tuner on it, along with other things. The main board has HDMI and the main processors on it. I've tested it with the control LVDS disconnected, and it does the same thing.

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Ugh! I feel like an idiot .

I should have checked the AC-DETECT pin. It's turning off exactly when the clicks happen. It's *normally* high but it sometimes goes low. It also goes low immediately if I unplug the TV, so it's "somewhat" working, but not completely.

Conclusions? Why is the AC-DETECT pin switching off? I have a feeling it's part of the problem. I'm thinking an optocoupler somewhere has failed, however rarely that may happen.

More circuit tracing...

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Okay, so I traced the AC detect pin. It goes straight into a microcontroller (U701) for the power supply, so I can pretty much forget about debugging that. However, I suspect it is getting a signal from somewhere else which isn't quite right.

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Okay, so I've made an executive decision to disable the AC detect optocouplers. They should now be always detecting AC. I'll see if this adversely affects the TV if it is unplugged - may lead to EEPROM corruption etc if so I will need to find an alternative.

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

YES! IT WORKS!!!!!!

Just bridged the two optocouplers... have never been so happy to hear that buzzing from the sustains & a no signal display!

Sorry bbjunkie, it looks like the boards are stuck with this TV...

It DOES however have some low level image retention and sparklies... I'm considering writing a tutorial about how to fix these as it's a common issue.

[bbjunkie]

Re: LG 42PC1D plasma - clicking repeatedly

Nice one tom66 - im still glad you were able to get it fixed - even if it means i wont get the boards!

Good luck with the concequences of the bypass

Jim

[tom66]

Re: LG 42PC1D plasma - clicking repeatedly

Nice one tom66 - im still glad you were able to get it fixed - even if it means i wont get the boards!

Good luck with the concequences of the bypass

Jim

Have tested it a few times.

I've noticed that without the AC detect even with a bright picture, TV lasts ~0.5 seconds with no power. With a dim picture, it's about 1 second. That's a serious amount of capacitance there.

I got it to tune into Freeview and I can clearly see the sparkles. Sustain voltages are good (except Vsc which I haven't tested) so on to timing!

Even after several power cycles while it is running, including turning off all power several times, it shows no signs of problems, so I'm going to call it fixed (apart from the sparklies.)