LCD fried - transformer to blame?

[mar345]

I had my ACER AL1916b blow up on me the other day and ever since have been trying to repair it. So I've been doing a fair bit of reading on the forums and followed the advice given to others, but unfortunately struck a dead end.

Basically the problem began with a bang that almost knocked me out of my seat. The LCD immediately switched off and couldn't be turned on anymore. I inspected the power board and noticed some bulged caps (CapXon) as well as the mos-fet chip (FSDM0565r) which had been blown apart (see pics which are all post-cap replacement). It took me a few days to find the rest of the chip as shown in the picture

I swapped all the caps on the board for new ones and also put in a new mos-fet chip.

However the monitor is still completely dead. I then checked voltages across the power board and noticed that the input side is apparently working well. There is 330V through the 400V capacitor. But there is no power at all on the output side after the transformer.

Therefore I suspect the transformer has shorted, which might explain why the first mos-fet exploded, although I don't understand why it didn't also blow the new one ive installed. The pins of the primary winding give a resistance reading of 0 ohms, as do the secondary winding pins.

Any suggestions on what to try next, or any other ideas in general?

I've tried looking for a suitable replacement for the transformer but it is hard to find.

[PlainBill]

Originally Posted by mar345

I had my ACER AL1916b blow up on me the other day and ever since have been trying to repair it. So I've been doing a fair bit of reading on the forums and followed the advice given to others, but unfortunately struck a dead end.

Basically the problem began with a bang that almost knocked me out of my seat. The LCD immediately switched off and couldn't be turned on anymore. I inspected the power board and noticed some bulged caps (CapXon) as well as the mos-fet chip (FSDM0565r) which had been blown apart (see pics which are all post-cap replacement). It took me a few days to find the rest of the chip as shown in the picture

I swapped all the caps on the board for new ones and also put in a new mos-fet chip.

However the monitor is still completely dead. I then checked voltages across the power board and noticed that the input side is apparently working well. There is 330V through the 400V capacitor. But there is no power at all on the output side after the transformer.

Therefore I suspect the transformer has shorted, which might explain why the first mos-fet exploded, although I don't understand why it didn't also blow the new one ive installed. The pins of the primary winding give a resistance reading of 0 ohms, as do the secondary winding pins.

Any suggestions on what to try next, or any other ideas in general?

I've tried looking for a suitable replacement for the transformer but it is hard to find.

While it is possible the transformer is shorted, that is unlikely. I would check my soldering work, then check the datasheet for the FSDM0565r and see if the voltages on the pins are reasonable. Also check if the diodes are shorted, in particular the one on the winding which provides running power.

PlainBill

[stj]

check the 3 fuses and all the pink resistors.

[mar345]

Thanks for the suggestions!

I checked the soldering jobs I did and all looked ok to me. I took a look through the FSDM0565r datasheet (http://www.fairchildsemi.com/ds/FS/FSDM0565RB.pdf) but couldn't really work out what voltages I should expect, although I have some idea. Regardless, I then checked the zener diodes like you suggested plainbill and I think two of them are shorted (readings of 15 ohm in both directions, the other is 9 ohm in both directions). All other diodes appear ok as measured in the circuit.

Looking again at the FSDM0565r datasheet, apparently when the chip is shorted one of these zeners is expected to blow (ZD102). Here is the relevant section: "Zener diode ZD102 is used for a safety test such as UL. When the drain pin and feedback pin are shorted, the zener diode fails and remains short, which causes the fuse (F1) blown and prevents explosion of the opto-coupler".

However all the fuses are not open, so this safety feature doesnt seem to have worked.

stj: I checked all pink resistors in circuit and they are ok. There are still 1 or 2 i need to take out to measure them which I will do soon.

I will go through the components again out of circuit and make sure there are no other problems, and will order in some zener diode replacements in the meantime.

Thanks again for your help plainbill and stj, I originally thought the problem had to be the transformer but now understand why it may be other components.

[PlainBill]

Originally Posted by mar345

Thanks for the suggestions!

I checked the soldering jobs I did and all looked ok to me. I took a look through the FSDM0565r datasheet (http://www.fairchildsemi.com/ds/FS/FSDM0565RB.pdf) but couldn't really work out what voltages I should expect, although I have some idea. Regardless, I then checked the zener diodes like you suggested plainbill and I think two of them are shorted (readings of 15 ohm in both directions, the other is 9 ohm in both directions). All other diodes appear ok as measured in the circuit.

Looking again at the FSDM0565r datasheet, apparently when the chip is shorted one of these zeners is expected to blow (ZD102). Here is the relevant section: "Zener diode ZD102 is used for a safety test such as UL. When the drain pin and feedback pin are shorted, the zener diode fails and remains short, which causes the fuse (F1) blown and prevents explosion of the opto-coupler".

However all the fuses are not open, so this safety feature doesnt seem to have worked.

stj: I checked all pink resistors in circuit and they are ok. There are still 1 or 2 i need to take out to measure them which I will do soon.

I will go through the components again out of circuit and make sure there are no other problems, and will order in some zener diode replacements in the meantime.

Thanks again for your help plainbill and stj, I originally thought the problem had to be the transformer but now understand why it may be other components.

The design description was definitely based on the 'old school' concept. In a modern design, the IC blows to protect the fuse, the zener shorts to complicate the repair and preserve the manufacturer's market for new monitors.

PlainBill

[almoodie]

Originally Posted by PlainBill

The design description was definitely based on the 'old school' concept. In a modern design, the IC blows to protect the fuse, the zener shorts to complicate the repair and preserve the manufacturer's market for new monitors.

PlainBill

That's funny.

Al.

[mar345]

Good News!

I finally got around to replacing the two zener diodes and the monitor is back to life. Thanks to those who helped and the badcaps forum in general.

An interesting note. A few weeks before the monitor crashed I noticed an unusual white blurring in the top left corner of the screen. Now that the monitor is repaired the blurring has disappeared.

The transformer now makes a whining sound that goes when the screen comes on. It may have done this before the repair.

[prj]

Hello,

I have the same issue...
All the caps except the big one have been replaced in the past, when this monitor was in warranty repair, and they are all good.

The FET (U101) blew up (blew half of it off, exactly like in OP's post), and also the 10V and 22V Zeners around it blew (ZD121, ZD120).
I replaced the FET (FSDM0565RB) and the diodes (10V and 22V 1W).

Now the monitor powers up fine, but after a little time it starts power cycling.
Turns out the FET gets very very hot and enters thermal shutdown... the heatsink is also very hot (I applied thermal grease, so it's not a head conductivity problem).

Any ideas what else to look for? What to test?

[PlainBill]

Originally Posted by prj

Hello,

I have the same issue...
All the caps except the big one have been replaced in the past, when this monitor was in warranty repair, and they are all good.

The FET (U101) blew up (blew half of it off, exactly like in OP's post), and also the 10V and 22V Zeners around it blew (ZD121, ZD120).
I replaced the FET (FSDM0565RB) and the diodes (10V and 22V 1W).

Now the monitor powers up fine, but after a little time it starts power cycling.
Turns out the FET gets very very hot and enters thermal shutdown... the heatsink is also very hot (I applied thermal grease, so it's not a head conductivity problem).

Any ideas what else to look for? What to test?

I would suspect every semiconductor, cap, and resistor associated with the gate drive on the FET.

PlainBill

[Rtech]

Would appreciate Supplier of the FET/SMPS Fairchild, as RS in the UK have had these on Backorder for over a year,and they are not available anywhere else.They also fail on the Hannspree M191W.

[prj]

Originally Posted by Rtech

Would appreciate Supplier of the FET/SMPS Fairchild, as RS in the UK have had these on Backorder for over a year,and they are not available anywhere else.They also fail on the Hannspree M191W.

http://uk.farnell.com/fairchild-semi...smd/dp/1467374

Originally Posted by PlainBill

I would suspect every semiconductor, cap, and resistor associated with the gate drive on the FET.

PlainBill

Uhm, I am afraid I am not good enough with electronics to quite understand what to check...

Here is the sample schematic from the FET's datasheet:


Here is the relevant part of the schematic of the power board:


What exactly should I test? Do I need a scope or is a DMM enough?

[Rtech]

The interesting thing about this,is that the part I need is the FScM056R,and yours is FSdM0565R,and certainly they are internally different,and typical circits are different,and I did get the (d) from Farnell and as far as I can see they are not interchangeable in the M19W1,Hannspree model.But while practically i'm fine,theory wise I'm no Einstein,so need perhaps more thoughts on these ??

[PlainBill]

Originally Posted by prj

http://uk.farnell.com/fairchild-semi...smd/dp/1467374


Uhm, I am afraid I am not good enough with electronics to quite understand what to check...


What exactly should I test? Do I need a scope or is a DMM enough?

ARGH!!! Please don't post images inline!! It REALLY creates problems when responding to a thread. Instead use 'Manage Attachments' below the text entry area.

In the datasheet schematic, it's C104, D101, and R103.

In the power supply schematic it's C115, D110, R113, R114, and ZD110.

I would say that you would have real problems testing these properly. They are operating at voltages and currents that most test equipment cannot simulate. If the resistors read the correct value they are most likely good. As for the cap, diode, and zener - who knows? If you have a parts list, I would suggest taking the shotgun approach and replacing the complete set of parts.

However, please note Rtech's comment. Are you sure you have received the correct part?

PlainBill

[prj]

Originally Posted by PlainBill

ARGH!!! Please don't post images inline!! It REALLY creates problems when responding to a thread. Instead use 'Manage Attachments' below the text entry area.

No offence, but it only creates problems if you re-quote them.
Of course, if it is the forum rules on this forum, then I will respect them.

In the datasheet schematic, it's C104, D101, and R103.

In the power supply schematic it's C115, D110, R113, R114, and ZD110.

Thanks.

I would say that you would have real problems testing these properly. They are operating at voltages and currents that most test equipment cannot simulate. If the resistors read the correct value they are most likely good. As for the cap, diode, and zener - who knows? If you have a parts list, I would suggest taking the shotgun approach and replacing the complete set of parts.

Zener - I guess I'll measure it both ways. But yes, it could not be completely shorted... or noisy... or whatever.
I don't have a parts list though. The service manual for the monitor does not have one.

However, please note Rtech's comment. Are you sure you have received the correct part?

Yeah, my old part is completely identical, I did verify this. It blew off the top, but the top plate was in tact, and it definitely says FSDM0565RB. Looks exactly the same too.
I am pretty sure something like "FScM056R" does not even exist. Google it, you won't get a single match besides this thread.

Anyway, it is possible to buy a such board for 20$ shipped (did not know that when I started to attempt fixing it), so if I am unable to repair this one, I'll give up, order a "new" (probably repaired) board from ebay and hope that it doesn't blow up the same way in 2 months.

EDIT:
Looked up FSCM0565R - that is a 5 pin part. Mine was a 6 pin part with pin 5 N/C. So yeah, I am 100% sure I have the right part.

[Rtech]

As long as you have the right part thats fine....there seems to be some confusion ref various data sheets,as you can see this CM0565R is 6 pin !!

http://pdf1.alldatasheet.com/datashe...SCM0565RG.html

[prj]

You were right.

On my board I do not have a separate R113 and R114.
I have them as one resistor - R113.
And measuring across that resistor measures 0hm both ways.

That means either ZD110 is shorted, or R113 and R112 are both shorted.
I suspect the diode. I will desolder the components and see where the problem lies.

Thank you!

P.S.
You were so right when you said this:

Originally Posted by PlainBill

The design description was definitely based on the 'old school' concept. In a modern design, the IC blows to protect the fuse, the zener shorts to complicate the repair and preserve the manufacturer's market for new monitors.

[prj]

Originally Posted by Rtech

As long as you have the right part thats fine....there seems to be some confusion ref various data sheets,as you can see this CM0565R is 6 pin !!

I see. But my board design and pinout matches FSDM0565RB, as does the part number.

It is definitely not the wrong part but rather what PlainBill pointed out.

[prj]

I verified R113, it reads the correct resistance.
Changed ZD110 and D110.

Still the same.
Turns on and starts cycling because FET overheats.

I did not replace C115... it is a ceramic capacitor...
Although I noticed that when I flex it back and forth on the board I hear a sound like something is cracking slightly, none of the other caps do that.

Perhaps I should replace C115 as well...
But at this point, I pretty much feel like giving up. I don't see myself repairing this board.

[neclicpasici]

Hello,

I had the same problem (a big BANG!) but on a different screen (Samsung 2232BW)

It has the same MOS-FET chip (FSDM0565r). I replaced it, but the screen was still dead.

Then I read your discussion, and I observed that my power board was very similar to your power board.

I did not have 13.5V at the output of this card.
So I replaced ZD101 and ZD102.

Now the screen works perfectly!

Thank you!
Sorry for my English

[PlainBill]

Originally Posted by neclicpasici

Hello,

I had the same problem (a big BANG!) but on a different screen (Samsung 2232BW)

It has the same MOS-FET chip (FSDM0565r). I replaced it, but the screen was still dead.

Then I read your discussion, and I observed that my power board was very similar to your power board.

I did not have 13.5V at the output of this card.
So I replaced ZD101 and ZD102.

Now the screen works perfectly!

Thank you!
Sorry for my English

It's obvious you were not educated in the USA in the past 20 years. Your English is excellent. And congratulations on repairing your monitor.

PlainBill