LG Flatron W2242S 'Dead in the Water'

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

Hi - Missed your previous post but the T101 is not for sale - I will get around to it at some point I have lots of "spares" to go at just need to work out the values for the diodes and
harvest some. I dont know why when they are so big (relatively) they cant print the value on instead of having to decipher a code.

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

Meanwhile, back at the T101, probing the high voltage primary. Bingo - 'the shakes' yield the spark I had been anticipating these past days. The Vcc voltage of 10.74V - derived from the 1 mA supplied via the 47K resistor attached to the 315VDC - is obliterated and leaves a residual 120 mV DC.

Obviously, the IC had been destroyed, as had the 33uF capacitor, and the 1N4007 which serves to rectify the Vcc supply from it's dedicated winding. YUK! I'm concerned about the potential lateral damage. Photo-coupler! Low wattage resistors and caps!

Right, time to replace the damaged items that I have literally 'cut-out' to ease the thermal stress when clearing the decks for new.

In goes the previously inserted FAN7601, followed by a brand new Panasonic 33uF cap, then a 1N4007 diode - that I couldn't believe remained in my junk box! A quick test confuses my Fluke meter ( and me). The diode pair associated with the 5v supply, are mounted on a heat sink - which is not at earth potential.

A call down to my Den 'Are you staying down there all day?' results in a diplomatic closure. Tomorrow, I will once again apply mains voltage.

P.S. No matter what. I have ordered that repaired Chinese replacement!

Never mind the Switching Transformer.

Believe it or not. It is refreshing to actually replace components that you have destroyed by accident!

Had to buy a spare PP3 Battery for the meter today. If the Fluke 'shuts down' I really have no alternative, other than the bin.

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

Ok I should have said the main thing I would need to test this board is budm.!!

Here is my board - I know its a mess - I have to say I have half given up on it as I dont need another monitor. Repaired it once with a new inverter transformer and replacing all the caps then 18months or so it just upped and died q101 blew taking out some diodes and the fuse. Replaced Q101 but couldnt bring myself to buying packs of 10 of each diode so I was waiting till I found some on other boards but project got shelved
So I would just set it up like this with the panel plugged in. Sheets of card between boards (including the button board - missed the card out on the picture though I would probably take the logic board off the frame as well.
I have put a tape on this board to highlight where C103 is - at least its the easier of the two to get at.
Pic 1 is out of focus sorry but you will get the general idea in pic 2 you could cover the bottom half of the board up to the white line with a bit of card
as you will be working above it.

Initially, I will ask if your T101 transformer is for sale?

As mentioned previously, I did insert a +5v & +22v supply refenced to chassis. This resulted in the Blue LED illuminating and the 22v circuit attempting to drive the invertor circuit when the On/Off button was pressed. ( totally disconnected from the mains - of course!) Unfortunately, my ancient Farnell variable supply is current limited to 500mA and you could observe the supply voltage collapsing to 15v as the inverter attempted to start ( with the backlights connected - two, and then, one. ) The wattage associated with the backlights would be appreciated.

Sure, I'm like a maniac striving to light that Blue LED! Agreed, a shorted turn within T101 should result in Armageddon for the switching circuit and associated semiconductor friends. Trouble is, Q101, when dynamically tested alone, behaved as an N channel Mosfet should.

Now, don't laugh. I've changed 'Fanny' the switching regulator for the third time! Ohmic readings of all three IC's have been extremely close to each other. WHY the changes? I told you about my rogue Weller soldering iron, which was overheating badly and needed human intervention to crudely control the tip temperature. For a start, the PCB is very poor quality base material, with an ultra thin copper track. Manual desoldering can easily carbonise the material below the copper track - creating unbelievable problems - especially when the carbonisation extends to adjacent pins!

The last IC replacement was made after cutting the copper tracks from at least four discoloured locations - purging the discolouration, and, using 36swg wire wrap, to re-establish circuit integrity. Needless to say, the fact that 315VDC was lurking at the IC, prompted these extreme measures.

You can almost hear the manufacturers saying " Mr Smith - in 5 years this product will self destruct," 'We have designed it to do just that!' The electronics ( hopefully) will prevent a conflagration - allowing us to use a degrading base to our PCB's that will brown and carbonise over time - destroying functionality.

Enough for this evening. I will 'hold off' buying a repaired board from China, until the battery runs out in my intermittent Fluke. Poor old AVO8 hasn't been able to throw me a 'life-line' for this investigation!

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

Have you tried to do any of the voltage tests?

Please do not take the hammer to it. As you say a new board can be had for £13 so if you dont want to go that route please offer it up on freectcle or freegle - if it was in my area I would be only too pleased to take it - a 22 inch monitor for £13.

[GERIATRICDAI]

Re: LG Flatron W2242S 'Dead in the Water'

It disturbs me to know I have to package the whole contraption, without knowing if the fundamental SMP supply is serviceable. What I mean is this. Without the interface to my original PC, there is the possiblity that the PSU in question, may be inhibited. You can guess where I'm coming from! Time spent in re-configuring the system, only to be 'kicked-in-the-face' if all is dead!

Right back at the start, I was bleating about the absence of either an 'Amber' or 'Blue' indicator lamp. Is it likely that either or both of these LED's are driven by the Logic Board? If so, where does the LED supply current originate from?

Essentially. the answer lies in the 'throw away mentality' with big bucks for those smart enough to recognise design weaknesses and cheap fixes. I believe you will still find the military insist on 'black box' philosophy and stand alone testing. Can you imagine a modern day Aircraft Technician, telling his Technical Officer - 'I need the whole aircraft, to complete this test!' Spare parts would be impossible, for an aircraft AOG - ( Aircraft on Ground).

Of course, if you are a B & O customer, you will be aware of the fantastic diagnostics they build in to their gear. Trouble is, could only afford it once! Strange to say, my Sony 26 inch Trinitron CRT TV, was unbelievably good at diagnostics.

For 'Follow-up' - I will advise when I use my 'Hide faced Hammer' to totally trash this current time wasting entity.

I am humbled by the generous contributions of top ranked subscribers, who must know the futility in dealing with geriatrics. Your tolerance is most gratefully accepted.

Before I close. 'About my Digital Hearing Aid Frequency Response!!!!!!!'

Seriously, long after I hang up my 'solder sucker' - you will be providing a most valuable service to future generations of folk who need all the help they can get.

Dai

[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 .

Good Man, I will study the chips behaviour under 'start-up' conditions.

Meanwhile, despite all the squeels of objection. Just pretend I wanted a multiple 5V and 22v dc supply, isolated from the mains, with a modest current capability. Let's say 1 amp at 5v and 500mA at 22v. The opto coupler has a part to play, normally. associate with failures.

Is this too much to ask?

P.S. The copper tracks are really ' one use only' unless you have your wits about you. This is 'one-shot' engineering . At it's best.

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

Ok I should have said the main thing I would need to test this board is budm.!!

Here is my board - I know its a mess - I have to say I have half given up on it as I dont need another monitor. Repaired it once with a new inverter transformer and replacing all the caps then 18months or so it just upped and died q101 blew taking out some diodes and the fuse. Replaced Q101 but couldnt bring myself to buying packs of 10 of each diode so I was waiting till I found some on other boards but project got shelved
So I would just set it up like this with the panel plugged in. Sheets of card between boards (including the button board - missed the card out on the picture though I would probably take the logic board off the frame as well.
I have put a tape on this board to highlight where C103 is - at least its the easier of the two to get at.
Pic 1 is out of focus sorry but you will get the general idea in pic 2 you could cover the bottom half of the board up to the white line with a bit of card
as you will be working above it.

[budm]

Re: LG Flatron W2242S 'Dead in the Water'

OK. if you look at page 10 of the app notes of the IC, D102 in page 10 is the same as D102 on your board.
C107 (connected to the VCC pin of the IC) in the page 10 is the same as start up cap C103 on your board.
C109 on the Latched pin 3 in page 10 is the same as C105 on your board.
So you need to find the safe way to measure the DC Voltage right at the two legs of the cap C103 (startup cap) on your board.
You should also check the resistor R109 on your board, it should be <1 Ohm.

[selldoor]

Re: LG Flatron W2242S 'Dead in the Water'

If you want something to read between responses then I suggest this
https://www.badcaps.net/forum/showthread.php?t=10419
Scroll down to post 19 that is the last update. Almost all the tests mentioned are
with a multimeter and mainly without power to the boards.

[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

[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?

[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!

[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'

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'

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

[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.

[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.

[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.

[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'

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!