LG Flatron W2242S 'Dead in the Water'

[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.

[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'

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.

[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.

[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

[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'

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!

[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.

[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.