LG 42PJ350 Click Click Clicking

[dicky96]

Hey guys I got a Plasma TV on my bench - first one I have ever looked at

I've done some googling and basic faulty finding already

When powered up the relays on the PSU go click-click-click every 5-10 seconds. I didn't time it but it's a regular repeating cycle like clockwork.

Also the owner says if you leave it plugged in, the TV will sometimes power up on it's own and then run OK for maybe an hour or more, then suddenly shut down again. I've not seen this myself but don't see why it would not be honest info.

I found this video https://www.youtube.com/watch?v=iLXfYZ6-iwQ and the fault seems to be the same symptoms and this guy also mentions the TV will sometimes power up.

As per the video I checked the fuses, 22R resistors and diode (out of circuit).

Now something is really puzzling me about this guy in his video. At around 3min 15sec he is testing the diode and says it is faulty because it has a forward voltage drop of 0.204 when a diode should have 0.4V-0.7V he says.

But the diode is a SB140A and even before I looked for the datasheet I knew this is going to be a Schottky Barrier Rectifier http://pdf1.alldatasheet.com/datashe...AY/SB140A.html and I always found these had a low forward voltage drop (even the datasheet says it has). Mine is reading about 0.16V on diode test range. So why is this guy saying that is faulty?

Anyway, I think the diode and resistors are OK, can't really test the 3BR1565 easily http://www.datasheet-pdf.info/entry/3BR1565 but would expect that would fail rather than sometimes work.

I found a couple of helpful threads on here too.

https://www.badcaps.net/forum/showthread.php?t=37974

I unplugged the X-Sus and Y-Sus and the power supply still click-click-clicks

Either with or without the X-Sus/Y-Sus I don't get any output on VS VA M5V even momentarily unless it is too fast for my Fluke 79 to see.

Disconnect the main board and it click-click-clicks once but does not do it again. Only rail with any output is STBY which is steady 5V both with and without main board attached.

No shorts on any supply rails on either XSus YSus or Mainboard connectors with boards attached.

Anyway sometimes it will work and shorted semiconductors don't tend to be intermittent.

But does disconnecting main board - and the clicking stops after first cycle - prove anything? Is there some pin on main board connector I need to apply a voltage without main board attached to force the PSU to run?

Or possibly I am down to the brute force method of pulling and testing all the caps on the PSU?

All look nice and clean and good visibly, but del3165 on other thread said that fixed his. Unfortunately he didn't say which caps and there are quite a few. I have ESR and Cap meter.

Any ideas to narrow this down a bit further?

Rich

[maxvalutech]

Re: LG 42PJ350 Click Click Clicking

Offhand from description sounds like power board is not responding to turn on signal so I think your right and time to check diodes caps etc and I would start with top rhs cap near Va.

[dicky96]

Re: LG 42PJ350 Click Click Clicking

Does anyone have a schematic for this PSU board?

I got the training manual from elektrotanya and that is of some help

I connected a link and a 100R resistor as described in the training manual to power up the 17V and 5V rails. They don't power up. It just goes click-click-click same as with main board applied

I didn't connect the 100W light bulb load to VS yet as I didn't connect the second resistor to power up that section of the PSU.

The training manual says to use 2x 100W light bulb in series as a dummy load. I can only assume that is for 110V bulbs, not the 220V ones i have?

I pulled all the electrolytics and tested for ESR and Capacitance. All are good. I changed the top right capacitor C901 (150uF 250V) anyway.

According to the training manual it is the microprocessor on main board that triggers the relays to turn on but something is still doing that with the main board disconnected - I am thinking that would be IC701 which actually drives the relays. I don't seem to find any datasheet about this chip other than this http://www.audiolabga.com/data_html/F4316MSF17.html

When I power up I get a quick flash on the light bulb limiter, when the relays click the first time my light bulb limiter flashes bright then goes off. On the second click it flashes very dim after that it stays off. I can see boost voltage 390V so looks like the PFC kicks in on the first click and charges the main electrolytics.

Holding my scope probe near the PFC inductors and main SMPS transformer primary I can see the PSU does drive the primary for a second or so on each click.

My only guess now is IC701 turns on the PSU, doesn't like something it sees, and turns it off again but without schematics/info I'm a bit stumped with this one at the moment

Can anyone help?

Rich

[maxvalutech]

Re: LG 42PJ350 Click Click Clicking

There is a service manual at diagramas.diagramasde.com Google that with model no.

[vinceroger69]

Re: LG 42PJ350 Click Click Clicking

Training manual

[dicky96]

Re: LG 42PJ350 Click Click Clicking

Hi guys
That is the service manual I already linked on my previous post at elektrotanya.

It is quite useful but has no schematics which is a right pain in the ass

I think next I will force the two relays on and see if I get any outputs from the SMPS

I don't think this will cause anything bad to happen as when the relays click, after the surge the first time when the PCF fires up, my limiter lamp does not light so it ain't drawing a lot of current

Rich

[R_J]

Re: LG 42PJ350 Click Click Clicking

Seem to be a bad ic (ice3br1065jf) possibly a diode and (2) 22 ohm 5 watt resistors, thats whats in the kit so I would check those parts.
This schematic might be close

[maxvalutech]

Re: LG 42PJ350 Click Click Clicking

I'm afraid the sensationalized schematics from page 25 on are all you can expect to get these days.

[maxvalutech]

Re: LG 42PJ350 Click Click Clicking

That should read sectionalised schematics - bloody predictive text!!

[dicky96]

Re: LG 42PJ350 Click Click Clicking

Cheers guys
@maxvalutech
I just don't get it - these sensationalised schematics lol don't give you the info you need to fix the PSU easily, but the circuit description goes into great detail how it operates. Really what is the point?

@R J
I will look at that schematic see if it is anything like

From investigating this fault with the relays forced on yesterday I have discovered a few things more. With relays on my 105W light bulb limiter now flashes bright every few seconds. This is with no load.

There are two separate SMPS controllers on this board plus the PFC which has it's own controller R2A20117

The ICE3BR1065JF controls the smaller standby SMPS. As well as STBY 5V this transformer also generates the M5V voltage rail and 17V rail.

When you connect a resistor to RLON as described in the service manual it actually supplies M5V from the same rail as STBY, it turns a serially connected FET on to feed 5V from STBY to M5V.

It does the same for 17V actually, the 17V ail is present even in standby but it has no load due to a serial FET being turned off.

In my case this SMPS is working and generating 5V and 17V so the ICE3BR1065JF is working along with the diode

Actually when my light bulb flashes bright the 17V rail drops slightly, as the PCF boost voltage also drops 20-30V

The larger SMPS is controlled by a L6599AD http://pdf1.alldatasheet.com/datashe...S/L6599AD.html with associated high and low side power FETs and this one generates the 200V-ish VS and 60V-ish VA voltage rails, This is the one that is not working

The 2x 22R 5W resistors are some party of the VS supply secondary circuit, not directly related to ice3br1065jf at all. They check OK on my board

Even when the bulb flashes bright I see no voltage on VS or VA even on my scope. Also I see nothing (or very tiny) high frequency pulses direct on VS secondary before the rectifier diode

Holding my scope probe on 50mV range near the primary of the VA/VS SMPS transformer I thought I see a burst of high frequency pulses when the light flashes but I see the same near the PCF inductors and 5V/17V SMPS transformer (which is running all the time)

This is acting like I have a short on VA or VS but I don't - unless a rectifier or Cap is breaking down under voltage. Something draws a lot of power at least 100W every few seconds - could be the PCF as the main caps discharge somewhat with light bulb flash, but even so then something in the VA/VS supply is loading the PCF boost voltage..

I considered removing the VA and VS rectifier diodes to eliminate short on secondaries at high voltages but a bit concerned this may really upset the controller L6599AD IC duty cycle - but then it says the is a High Voltage Resonant Controller that modulates frequency not duty cycle? I don't know anything much about this SMPS architecture, need to go google some I guess.

As I don't have my isolation transformer here (it's heavy and still in UK) can't I just disconnect my Rigol 1502 Scope earth so I can connect scope ground lead to hot ground and probe the L6599AD.

Yes I know the scope ground then floats at up to mains potential but the Rigol internally has a SMPS so the probe circuitry and 'ground' isolates from the mains live/neutral there, and anyway it is made from plastic apart from the BNC ground and a couple connectors on the rear.

Everywhere you google says this is really dangerous, yet in the early 80's when I did my City&Guilds in TV repair we were taught by our instructors to float the scope when working on TVs. Unless you were lucky enough to work in a shop with isolation transformers.

No TVs had an earth connection then anyway, they were all captive leads with two conductors.

In the Valve sets and earlier transistor sets the chassis was connected to neutral

If the TV was one of those new fangled 1970/80s designs that used a full wave bridge followed by a 100Hz Thyristor 'chopper' circuit to regulate the supply voltage by chopping a chunk out of the mains half cycle, then the whole chassis was connected to the bridge rectifier negative terminal and floated at what they called 'half mains voltage' - which actually meant 'full mains voltage for half of the time'

Depending which half cycle of the mains was coming out of the rectifier at that instant the chassis was either at Neutral or Live potential!!

So your floating scope (which you were careful not to touch the metalwork) was only at the same potential as the entire TV chassis you were working on anyway - which you were equally careful not to touch!

So what I don't get is why it is more dangerous and a huge NO NO with a modern plastic scope to do what was normal practice with a metal scope back in the day???

Surely if you understand and respect what you are doing this is as safe (or even more so due to almost no exposed metal on a Rigol) for you, your test equipment and the DUT as it was in the 80s??

Rich

[maxvalutech]

Re: LG 42PJ350 Click Click Clicking

Sorry I only have phone view and can't read connector info so is there a Vs-on switch that also needs forcing when power board isolated and powered on. I'm not up on LG but many tv makers bring in power supplies from outside in which case the circuit is not included in their manuals. Only a few on here would work down beyond basics of the usual troublemakers such as diodes caps FETs etc before going to board replacement which can be cheap and easy.

[Amraks]

Re: LG 42PJ350 Click Click Clicking

I have the same Model Plasma here exact same fault.
replaced a Chip in it worked for a year then failed with this symptom.

Will be working on it when after the weekend.

[Amraks]

Re: LG 42PJ350 Click Click Clicking

As I don't have my isolation transformer here (it's heavy and still in UK) can't I just disconnect my Rigol 1502 Scope earth so I can connect scope ground lead to hot ground and probe the L6599AD.

Yes I know the scope ground then floats at up to mains potential but the Rigol internally has a SMPS so the probe circuitry and 'ground' isolates from the mains live/neutral there, and anyway it is made from plastic apart from the BNC ground and a couple connectors on the rear.

Everywhere you google says this is really dangerous, yet in the early 80's when I did my City&Guilds in TV repair we were taught by our instructors to float the scope when working on TVs. Unless you were lucky enough to work in a shop with isolation transformers.

No TVs had an earth connection then anyway, they were all captive leads with two conductors.

In the Valve sets and earlier transistor sets the chassis was connected to neutral

If the TV was one of those new fangled 1970/80s designs that used a full wave bridge followed by a 100Hz Thyristor 'chopper' circuit to regulate the supply voltage by chopping a chunk out of the mains half cycle, then the whole chassis was connected to the bridge rectifier negative terminal and floated at what they called 'half mains voltage' - which actually meant 'full mains voltage for half of the time'

Depending which half cycle of the mains was coming out of the rectifier at that instant the chassis was either at Neutral or Live potential!!

So your floating scope (which you were careful not to touch the metalwork) was only at the same potential as the entire TV chassis you were working on anyway - which you were equally careful not to touch!

So what I don't get is why it is more dangerous and a huge NO NO with a modern plastic scope to do what was normal practice with a metal scope back in the day???

Surely if you understand and respect what you are doing this is as safe (or even more so due to almost no exposed metal on a Rigol) for you, your test equipment and the DUT as it was in the 80s??

Rich

mains earth grounded.
Dave explains it in this video.
https://www.youtube.com/watch?v=xaELqAo4kkQ

[dicky96]

Re: LG 42PJ350 Click Click Clicking

@maxvaluetech

Yes the manual says you need to add two 100R resistors and a ground link to plug P301 with main board and X/Y sus boards disconnected

A) Ground the Auto Gnd Line (Pin 18) will allow the supply to be powered up one section at a time.

(B) Add a 100 Ω ¼ watt resistor from 5V Standby to RL_ON and the 17V and 5V Run Lines on P813 will become active. Also AC-Det and Error_Det will go high.

(C) Add a 100Ω ¼ watt resistor from any 5V line to M_ON (Monitor On) to make the M5V, VS and VA lines operational.

I did that but get no VA / VS
Rich

[dicky96]

Re: LG 42PJ350 Click Click Clicking

I did find another 'repair kit' for this same PSU fault so will look at those components to see if they are in the VA/VS SMPS circuit

http://www.ebay.co.uk/itm/LG-42PJ350...sAAOSwXshWrntC

KIT CONTENTS R103 / R104 / R105 / R106 / R107 / R108 / R109 / R110 / R111 / R112 / R113

[Amraks]

Re: LG 42PJ350 Click Click Clicking

dicky96 any updates on this did it fix the issue?

[dicky96]

Re: LG 42PJ350 Click Click Clicking

HI, sorry been busy with this and that......

The R103-R113 kit is part of the circuitry for the ICE3BR1065JF which is the lower powered SMPS. I didn't look exactly at the values but the resistors are surface mount and in series/parallel arrangements so almost certainly they are for current sense and/or startup supply for the 3BR1065

As this SMPS is working on the board I have, I didn't go any further with it.

I've kinda put this on one side until I can sort out an isolation transformer and work on the primary side to see where the real problem is

Rich

[Amraks]

Re: LG 42PJ350 Click Click Clicking

Finally got around to doing this tv

I disabled the protection circuit by keeping on pc101 by bridging on cold side to force the tv on so I could test the voltage drop on the resistors network the r111 is showing a very large drop, I then took this out of circuit and confirmed its not 680kohms anymore and its reading in mohms so I would say this is the problem.

[Amraks]

Re: LG 42PJ350 Click Click Clicking

I disabled my bridge override pc101 and
I replaced R108 / R109 / R110 / R111 / R112 / R113 Tv now works and doesn't turn off.

[valiant81]

Re: LG 42PJ350 Click Click Clicking

Hi Guys; I'm a retired television teck and have a problem with a LG 42pj350.This is a Australian imported set. This set will work if i put it into the service mode by removing the LVDS cable from the main board, then installing a wire link on the t-con board. Doing this puts the set in to the self test mode and the screen will display a set of B/W and color test patterns, Doing this simple test will tell you that the power supply and all of the drive boards are working and this only leaves the main board. trying to find a working main board in Australia is like tying to find a needle in a haystack.!!!
Does any one on the forum have a main board in Australia they would be able to sell me , otherwise i'm afraid this set will be going into land fill or broken down for the boards and screen.