LG Flatron W2242S 'Dead in the Water'

[GERIATRICDAI]

Hi Afficionados,

I have followed some of your excellent efforts and advice whilst exploring my options with the faulty power supply. For the record, the inverter transformer secondary readings were within .1% of each other ( 964 ohms on my Fluke MM). Please be advised, I have long been without my sophisticated electronics gear. Now down to an AVO 8 and my intermittent Fluke!!

Meanwhile, let me advise, China sent me two replacement SW chips, I replaced the original, and had the benefit of seeing 'LG' appear on the screen - shortly afterwards, when selecting the 'Menu Button' - total failure - as per original fault. I should state ' the monitor was simply 'stand alone'. I make the assumption that the lack of the 'Blue or Amber' indicators tends to point to a failure of the SW PSU.

Needless to say, I have purchased a full set of Panasonic replacement capacitors, even though there is no physical 'bulging' - and, as stated previously, I cannot test a capacitor to a specification.

Meanwhile, I really would appreciate advice regarding the readings associated with T101. Essentially, although no signs of distress, the readings all average 'Zero ohms' across the respective windings.

I must admit, with 320VDC on the primary winding, I would expect something more than near zero ohms across terminals 3 & 5.

Finally, as a 'rookie' on this incredibly useful facility. Please accept my apologies if my submission appears presumptious or condescending.

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

In the absence of any pictures I am guessing T101 is the main TRansformer.
They rarely fail and it is usual for them to read zero ohms

You may have been better adding to another thread then information that you have would be more easily available as now it has to be gathered - takes too much time so we often dont bother.
I will have a look in tomorrow if its not been fixed overnight

[budm]

Re: LG Flatron W2242S 'Dead in the Water'

"the readings all average 'Zero ohms' across the respective windings" That is the DCR of the transformer winding, yes, it will be very low but it will have high impedance when swithcing DC is applied to the winding. Did you check the snubber circuit for that IC?
What is the P/N of that SMPS IC?

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

Hi,

Good of you to take an interest.

U101 is a LAF0001 which I replaced with replacements from China, and had the pleasure of seeing that blue light illuminate, followed by the LG Logo and lasting all of 10 seconds - then, back to being an inert lump!

I must admit, without the means of viewing things dynamically, it's a bit like 'throwing snowballs at the Moon.' This is where I have to rely heavily on those folk with experience.

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

Can you post good pictures of the power supply board - front and back so we can see what we are dealing with. Please use manage attachments jpg less than 3mb
Did you have a source connected when you were testing - working PC. - some monitors dont stay on without a signal.

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

Testing took place with the monitor 'stand-alone'. Is it just possible that an initial power-up would have illuminated the blue LED and displayed the LG Logo? Surely, any subsequent attempt to switch the monitor on, would result in the same sequence.

Now, let me try and attach some of the photographs requested.

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

You are correct - misread it -did not realise you are now back to dead
Why did you decide to change the U101 originally?
There is a Diode D102 connects to it that looks as if it has been hot.
can you test using ohms..
Did you test the mosfets on the back of the board.



Do you still have 300+vDC on the BIG cap

[budm]

Re: LG Flatron W2242S 'Dead in the Water'

OK, just the power supply/inverter board by itself with power applied, do you get any DC voltages at the white connector?

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

You are correct - misread it -did not realise you are now back to dead
Why did you decide to change the U101 originally?
There is a Diode D102 connects to it that looks as if it has been hot.
can you test using ohms..
Did you test the mosfets on the back of the board.



Do you still have 300+vDC on the BIG cap

U101 - why change? Cheap and cheerful - easy to remove, and replace, with a modicum of care. Past experience with folk finding their bedroom LCD TV kaput, usually associated with leaving the damn thing on 'standby' all night. That's one of the problems with the UK's 230VAC supply - we are so easily subjected to overvoltage transients that exceed the upper limits of the equipment. 20 milli-seconds is forever to a Switch Mode Suppy.

I can cite a number of chip replacements that cost less than a pound and restored full functionality - without the need for the services of the true diagnostic experts.

As for D102, a bog standard 1N4007, which passes the Fluke diode test.

I ignored the Mosfets on the underside, simply because my main concern is the absence of 5v & 22v DC supplies.

I configured the board with a load resistor across both the 5v & 22v electrolytics - approx 6W loading, in each case. Apply mains connector - 313vdc at the big storage capacitor - ditto at the drain of Q101, AND pin 1 of U101. This is where 'I lose the plot' as to how this chip starts the sequence of switching and generating the appropriate voltages.

Phew, my concentration levels aren't up to this!

C'mon fellow engineer, how do I kick start my 'Massey Ferguson' power supply - in easy to understand, terms.

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

OK, just the power supply/inverter board by itself with power applied, do you get any DC voltages at the white connector?

The measurements I make, are always at the storage capacitors. Too often, a slip of the probe generates a 'court case - citing negligence for blowing up a perfectly good piece of equipment'. As you get older, try to avoid the shaking hand, trying to target a pin - 50 thou removed from it's neighbour. By all means, have a specially made up test connector, for the equipment under test. Time consuming and not really practical - although a delightful theoretical asset!

In this instance, we had the 'one hand in pocket'- negative lead placed firmly at the appropriate point, then, that free hand, will move the positive probe to where ever desired. WHY this Palava?

You must prevent the current from a electric shock, passing across your chest

Believe me, if you lean across anything holding two probes at the ready, you may never make that reading!

[budm]

Re: LG Flatron W2242S 'Dead in the Water'

That white connector is on the cold side which the circuit ground is also connected to the chassis, so yeah, do not touch anything in the primary hot side. I myself use outlet with GFI and Isolation transformer on what I am working on.
BTW, do you have the spec sheet of that SMPS IC u101 LAF0001?
Never mind, it is the same as FAIRCHILD FAN7601.
Startup cap connected to VCC pin shows 0V?

From app notes: Page 2.
2. Device Block Description
1. Start-up Circuit And Reference
The FAN7601 contains a start-up switch to reduce power
loss in the external start-up circuit of conventional PWM
converters. The internal start-up circuit charges the Vcc
capacitor with a 1mA current source if the line is connected
until the soft start is completed as shown in Fig. 2. The soft
start function starts when the Vcc voltage reaches the start
threshold voltage(typically 12V) and it ends when the
LATCH/SS pin voltage reaches 1V. The internal start-up
circuit starts charging the Vcc capacitor again if the Vcc
voltage is lowered to the minimum operating voltage
(typically 8V). In such a case the UVLO block shuts down
the output drive circuit and some other blocks to reduce the
IC current, and the soft start capacitor is discharged to zero
voltage. If the Vcc voltage reaches the start threshold voltage,
the IC starts switching again and the soft start capacitor
is charged from zero voltage. The internal start-up circuit
supplies
current until the soft start is completed .

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

That white connector is on the cold side which the circuit ground is also connected to the chassis, so yeah, do not touch anything in the primary hot side. I myself use outlet with GFI and Isolation transformer on what I am working on.
BTW, do you have the spec sheet of that SMPS IC u101 LAF0001?
Never mind, it is the same as FAIRCHILD FAN7601.
Startup cap connected to VCC pin shows 0V?

From app notes: Page 2.
2. Device Block Description
1. Start-up Circuit And Reference
The FAN7601 contains a start-up switch to reduce power
loss in the external start-up circuit of conventional PWM
converters. The internal start-up circuit charges the Vcc
capacitor with a 1mA current source if the line is connected
until the soft start is completed as shown in Fig. 2. The soft
start function starts when the Vcc voltage reaches the start
threshold voltage(typically 12V) and it ends when the
LATCH/SS pin voltage reaches 1V. The internal start-up
circuit starts charging the Vcc capacitor again if the Vcc
voltage is lowered to the minimum operating voltage
(typically 8V). In such a case the UVLO block shuts down
the output drive circuit and some other blocks to reduce the
IC current, and the soft start capacitor is discharged to zero
voltage. If the Vcc voltage reaches the start threshold voltage,
the IC starts switching again and the soft start capacitor
is charged from zero voltage. The internal start-up circuit
supplies
current until the soft start is completed .

You are a most welcome contributor. I will try to understand those early microsecond activities. Thanks for the contribution.

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

By the way, the replacement chip, is exactly as you specified. I had no alternative, other than, to believe the blurb. I'm pretty sure all is well regarding the specifications.

[budm]

Re: LG Flatron W2242S 'Dead in the Water'

The key right now is to see if the VCC of the startup cap does get charged up to 12V required to start, it can be typical bad startup cap problem. You also may want to resolder those pins on the IC.

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

As you get older, try to avoid the shaking hand, trying to target a pin - 50 thou removed from it's neighbour.

Here is a tip that might enable you to do the low voltage tests directly on the
connector. You dont need a special rig just a sewing needle.

All you do is anchor the negative lead of your meter to a ground screw then
push the needle into the socket alongside the wire to the pin you want to test.
You can then touch the red probe onto the needle. So a one hand job.
You can put the pin in position with no power to the board then just power on to do the test.If you need more protection from slips you can pop a card disk over the needle.
I have set up some pics using old board and probes

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

Here is a tip that might enable you to do the low voltage tests directly on the
connector. You dont need a special rig just a sewing needle.

All you do is anchor the negative lead of your meter to a ground screw then
push the needle into the socket alongside the wire to the pin you want to test.
You can then touch the red probe onto the needle. So a one hand job.
You can put the pin in position with no power to the board then just power on to do the test.If you need more protection from slips you can pop a card disk over the needle.
I have set up some pics using old board and probes

An excellent suggestion and probably capable of saving many a scuppered vessel due to nothing but 'the shakes'. Have you noticed how probe technology still believes we are clamping our probes onto 50W wire wound resistors! However, in this instance, I did wish the power supply board to be completely separated from those that normally feed from it. A crude attempt to provide the nominal loadings for both the 5v and 22v circuits, using incandescent lamp bulbs, was a 'no brainer' - the filament cold resistances were practically short circuit values - so, they were dumped, in favour of some WW resistive loads - which I do not posses!! I could spend a fortune buying all sorts. Believe it or not, there is a source for this board in China, at £13 - postage free! Trouble is, we all want to know who the villain - or weak component, is, RIGHT? Oops sorry, slipped away from the 'needle in the connector' solution. Without a 'white connector' plug installed, we are left with the 'glistening teeth' of connectors daring us to 'cross fertilise' them - by the expedient of trying to take measurements where only a fool would venture. I know, we are right back to the merits of owning blank plugs that can be inserted into sockets - simply to facilitate the excellent technique you advocate.

For the record, the incandescent loads, created the most weird rectifier diode readings - I suspect because of the shared secondary windings between the 5v & 22v circuits.

Meanwhile, hopefully, back to those 10 microseconds when the extensive protection circuitry prevents the destruction of dynamic ciruitry.

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

No - to test the secondary voltages , most of the time you need to have the plug in.
When you have the plug out the power supply will most likely switch off most of its circuits.
- if you check the picture the plug is in and you push the needle beside the wire and it will connect with the metal that goes over the pin.

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

The key right now is to see if the VCC of the startup cap does get charged up to 12V required to start, it can be typical bad startup cap problem. You also may want to resolder those pins on the IC.

You really have provided me with some excellent material. Right now, I do possess a full set of genuine Panasonic elecrolytics. Would you like to suggest the first I should replace - rather than a blanket replacement? I must admit to being nervous on seeing 313VDC appearing at pin 1. As for re-soldering the IC pins? My Weller Soldering Staion PS3 has started to behave like a pig - either roasting, or cooling . However, I can still manage to de-solder and re-instate without destroying the beast. Damned if I can do with a soldering iron failure, as well?

I suspect you will 'ease me along' the 'start-up' scenario. Fingers crossed!

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

No - to test the secondary voltages , most of the time you need to have the plug in.
When you have the plug out the power supply will most likely switch off most of its circuits.
- if you check the picture the plug is in and you push the needle beside the wire and it will connect with the metal that goes over the pin.

I do understand where you are coming from. Nevertheless, had you this board in front of you, to check it's functionality, what would you require to test it?

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

I have almost that board in front of me - and a cheap multimeter.
For most monitor repairs that is all that is needed plus soldering equipment
and a needle, Budm can talk you through all of it and I can chip in with what little I know. Only other thing might be a spare bulb but a test one can be made from a domestic cfl 14w or less. Oh and a magnifying glass but no dummy loads.
Start up cap is either C103 or C105 Budm will know. Both are connected to the replacement IC one is a lot easier to get at than the other. When you are ready to test them perhaps tape over the surrounding area with insulation tape.
I am off to bed now. Evening time coming up for budm