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Old 07-02-2011, 06:17 PM   #1
momaka
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Default I need help fixing a Sony GDM-FW900 24 CRT

I got two of these awesome monitors on Craigslist in the winter. Both were not working, but it seems that one just had a loose wire on the power supply board because when I swapped the PSU boards back and forth, that monitor now seems to function fine with either PSU board. The other monitor still has a problem, though, and it’s the same regardless of which PSU board I use (it was like that before I even opened that monitor).

Basically, when I plug power to the broken monitor, it sounds like it tries to start up; at first, I can hear a buzz (the degauss coil coming on), but then I hear a high-pitched screeching (about 1 second in length) followed by a click after which the screeching stops. The monitor then tries to power on again and the above scenario repeats (relay clicks, screeching noise, relay clicks again and screeching stops).

With the back of the monitor and the top shield removed, I can clearly see spark gap SG901 begins to conduct when the monitor tries to power up and the screeching begins. This spark gap is found on the D board (deflection board?) very close to the HV flyback transformer. It seems that the high-pitched screeching also comes from that area.

The schematic for this monitor can be found here:
http://esi.sony.ca/esupport/esupport.../997867901.pdf
Page 31 has a schematic of the D board circuits.

So, does anyone know what could be causing this issue and what to look for? I don’t have much experience with CRT monitors and TVs (only fixed one CRT monitor that had PSU problems).

In any case, I’m sure the D board will have to be removed to check/change components. However, what’s stopping me from doing so is the anode cap on the CRT tube – I just can’t get it off. Does anyone have any tips on how to remove it? Or is there any special method? The service manual above does show how to do it, but I’m unable to for some reason (can't get past separating the protective rubber cup from the CRT tube… the closest I've gotten is to just get the anode cap a bit loose but that’s it). I don’t want to damage it.

If I can get the D board off, then I'll be able to check some of the components myself and also take some pictures, if that helps.
Also, I think I might have to remove the board that attaches on the back of the CRT tube. Anyone know how I should do that? Just pull the board from the socket or is there something more special to it?

Any other help and tips are welcome too. Would be great to get this monitor working again. The picture on the other one is great. Would be a shame if I do not fix it.

The only reason I got these monitors is because no one wanted them. Owner said he first put them on CL for $30 the first week, but no one responded. Then he tried $15 and still got no replies. Finally he put them up for free, but still no responses. I guess I got lucky because when I talked to him afterwards, he said was getting ready to put the monitors on the curb that week but didn't only because they weigh so much (and he didn't want to call e-recyclers cause they wanted too much money). So he ended up putting them on CL again. After a week of no one replying again, I saw the posting, literally minutes before it expired, and emailed him. I didn't expect anything, but when I got his email I was pretty surprised. So yeah, I guess I got really lucky (and the monitors too – otherwise dump truck would have crunched them).

Anyways, thanks in advance everyone (and as usual, sorry for the long post).

Last edited by momaka; 07-02-2011 at 06:28 PM..
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Old 07-02-2011, 06:29 PM   #2
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

You likely have a bad flyback on the second set. The spark gap is a good evidence of that. And man, a FW900??? I always wanted one but they were too expensive a couple years ago, and no luck nowadays.
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Old 07-03-2011, 10:14 PM   #3
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Quote:
Originally Posted by Th3_uN1Qu3 View Post
You likely have a bad flyback on the second set. The spark gap is a good evidence of that.
Yeah, I thought that might be the problem too, since the spark gap is right next to the flyback on the schematic. I was just hoping someone would tell me otherwise .

Any ideas how to get the HV anode cap off? (Sorry for the noobish question).
I'm still going to check all of the components on the deflection board (once I get it out). Are there any particular components the flyback could have taken out when it died?

Hopefully they still sell flybacks for those things.

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And man, a FW900??? I always wanted one but they were too expensive a couple years ago, and no luck nowadays.
Yup, FW900 ^_^ .
Actually, I didn't even know they made widescreen CRTs (or that big) prior to getting these 2 beasts. Always thought the biggest monitor you could get with CRT was 21" 4:3 aspect ratio and that's it. I was so happy, I actually paid the guy $10, even though he didn't want any money (I had to give him something!). It was instant love when I saw the monitors .
...
I think I posted a picture here on another thread as well...
...
Yup, here: http://www.badcaps.net/forum/showpos...5&postcount=32
The monitor in that picture is actually the Sony I got working. The non-working monitor is the HP-branded version (model GDM-FW9012). They are absolutely identical, though.
Wish I could give you this broken one because I'm sure you can fix it. Shipping from US to Romania would be an absolute killer, though.
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Old 07-04-2011, 11:53 AM   #4
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Quote:
Originally Posted by momaka View Post
Any ideas how to get the HV anode cap off? (Sorry for the noobish question).
Grip it firmly from the sides and wiggle it around till it comes loose. Do not use a screwdriver or you may damage the tube. As for REALLY BIG CRTs, there's the Sony XBR lineup. Some of 'em are Full HD too. And yes you can use them with your computer.

Last edited by Th3_uN1Qu3; 07-04-2011 at 11:55 AM..
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Old 07-05-2011, 12:48 AM   #5
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Quote:
Originally Posted by Th3_uN1Qu3 View Post
Grip it firmly from the sides and wiggle it around till it comes loose. Do not use a screwdriver or you may damage the tube.
Thanks. Yeah, service manual said the same thing about not using a screwdriver, so I'll follow that too. I think I was being too gentle with it the first time, though .
Will take it apart sometime this week and start testing. I can post pics too if anyone is interested.

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As for REALLY BIG CRTs, there's the Sony XBR lineup. Some of 'em are Full HD too. And yes you can use them with your computer.
Those I know about. WLG here got a set like that about a year ago, it's 16:9 1080i/720p (don't remember the thread name, though). Pretty nice TV.
I'll take one any day over a big LCD with washed-out colors (like my parents'). Heck, I still like our SD 32" Philips tube TV better than my parents' LCD TV. Unfortunately, I have a feeling they'll be getting rid of it sometime this or next year.
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Old 07-05-2011, 09:34 AM   #6
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

If it isn't a big deal (albeit it usually is), try the tube in the bad monitor with the boards in the good one, to make sure it's worth fixing. If you're really lucky you'll be able to extend the wires to reach the other tube without removing the good board from its case.
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Old 07-06-2011, 01:46 AM   #7
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Ah, finally got the D board out! Had to take everything apart. Took quite a bit of work.

Quote:
Originally Posted by Th3_uN1Qu3 View Post
If it isn't a big deal (albeit it usually is), try the tube in the bad monitor with the boards in the good one, to make sure it's worth fixing.
Yeah, in this case it is a bit of hassle. The service manual shows that you can easily take out the D board (deflection) without disturbing anything else, but that's not true, because there are two wires that extend from the flyback transformer to the socket on the CRT tube. Therefore, the board that attaches to the back of the CRT neck (the A board) needs to be removed as well - there's no way to detach the two wires without doing so.

But even when the A board is removed and two wires are detached from it, the connector that holds these two wires is too big to fit in the hole that exists between the CRT tube neck and the metal backplate that holds the A board.

Thus, that backplate needs to be either removed or pulled back a few inches to allow the connector to come out. For this backplate to come out, the PSU board also needs to be removed. In addition to that, the S board is attached to the backplate as well, so some wires need to be detached from the S board so that it can be pulled out with the backplate. Finally, before removing or pulling the backplate, first the D board needs to be partially taken out so that it clears the backplate, then the backplate (and thus the connector with the 2 wires) can be removed.
After all of this, the D board can be funally taken out.

So given all of that, I don't think I want to take apart the other monitor (at least not for now ). There's lots of things for me to screw up too, and that other monitor is working fine. Don't want to break it if it's working.

Quote:
Originally Posted by Th3_uN1Qu3 View Post
If you're really lucky you'll be able to extend the wires to reach the other tube without removing the good board from its case.
Unfortunately, that's not possible with this monitor. HV tube wire is very short. It barely reaches the tube even when it's properly in place. Same goes with the wires for the other boards. I guess Sony tried to make it all neat inside by keeping the wire lengths short (and they did - it's a pleasure to look at). In fact, the wires are so short that I can only partially take out most of the board, and then I have to reach inside the monitor with my hand to disconnect various connectors - good thing there weren't any charged capacitors.

I included a couple of pictures below to show you what it looks like.
First pic shows how the boards are arranged in the monitor. The D board is the one that is taken out on the side; normally it's positioned vertically just like the board on the left side (the G board).
Second pic shows a closeup of the D board. Nothing looks bad so far, but when I get time, I'll start checking out components. There's lots of SMD stuff on the back too.
Attached Images
File Type: jpg GDM-FW900 assembly overview (2).jpg (277.2 KB, 56 views)
File Type: jpg GDM-FW900 D board (1).jpg (312.2 KB, 44 views)
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Old 07-06-2011, 04:34 AM   #8
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

probably the fly but make sure the crt has not gone to air.
thats what buried mine.i saved the boards but when the bottom fell out of the crt market i tossed them.
i rarely get pc crt's in for repair anymore.plenty of industrial though.
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Old 07-06-2011, 05:38 AM   #9
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Quote:
Originally Posted by momaka View Post
Will take it apart sometime this week and start testing. I can post pics too if anyone is interested.
I'm interested!

I wish I could help you fixing that monitor, you helped me many times with psus and more, but I don't know how to fix CRTs yet..

I have opened a thread that is a learning project for me: http://www.badcaps.net/forum/showthread.php?t=14863

This is a great guide about CRT repair, I wish it wasn't so long...
http://www.repairfaq.org/samnew/tvfaq.htm

And some interesting you tube videos:
http://www.youtube.com/watch?v=vsFqdPYzsjo
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Old 07-08-2011, 03:06 AM   #10
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Quote:
Originally Posted by kc8adu View Post
probably the fly but make sure the crt has not gone to air.
Sorry if I'm asking dumb questions again, but do you know how I can check that (that the tube isn't bad)?

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Originally Posted by kc8adu View Post
thats what buried mine.i saved the boards but when the bottom fell out of the crt market i tossed them.
i rarely get pc crt's in for repair anymore.plenty of industrial though.
Wish I knew more about CRTs. Seems that their time is gone now.

Quote:
Originally Posted by goodpsusearch
I have opened a thread that is a learning project for me: http://www.badcaps.net/forum/showthread.php?t=14863

This is a great guide about CRT repair, I wish it wasn't so long...
http://www.repairfaq.org/samnew/tvfaq.htm
Thanks for the links. I actually really do need a good reading on the CRT technology. It may be obsolete, but I still find it interesting.

Also, I do remember seeing your thread back when you opened it, but due to lack of knowledge on the matter, I just didn't know what to suggest. Now that you found the two bad resistors, maybe we can find something.

----
As far as progress on my monitor - I just spent about 1 hour today decoding the service manual to get a better idea of what different things do on the D board. So far I feel like I have a very very basic understanding on the HV, Horizontal, and Vertical drive sections. Still haven't checked much on the D board, though. Have an upcoming exam this week that I need to study for so will see what I can get done with this.
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Old 07-08-2011, 03:22 AM   #11
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

best test is to move good chassis to tube you want to test.iirc these have akb so focus may be the only setting you need to touch.maybe convergence in the menu.
or a good crt tester like my b&k 467.
since you did not see the failure its hard to tell.mine went from looking good one day to occasional arcing the next to symptoms you describe.it went soft too.these tubes are prone to leaking.i suspect these will be the 15gp22 of crts in 50 years.
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Old 07-08-2011, 10:37 PM   #12
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

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Originally Posted by kc8adu View Post
best test is to move good chassis to tube you want to test.
I guess that's the best option really. Or perhaps just replace the flyback and hope it works.

Getting a new flyback may be a problem, though, because I can't seem to find a new one anywhere online. Sony's serviceplus website says it's under maintenance until July 18.
Actually, there are a number of places listing it online, but none have it in stock. I think I only saw one or two websites that said they'll do a special order.
Bottom line is, I didn't find any FBT for less than $100. Not sure I want to spend that much. Still, anyone know where I can find these FBTs in stock? Part number on FBT is nx-4504 or 1-453-348-11.

If not, I guess I might just give this monitor out on Craigslist again.

I wonder if I can test the HV output from the FBT in some way...
like what if I connect the deflection board back in the CRT but leave the anode cap unconnected and put it close (about 1-2 cm) from a metal ground to see if it arcs over? I know that won't be a definite test for the FBT, but do you think that would be a good go/no go test to see if HV is there?

The other idea I have is this: could I use a flyback from a different monitor or TV, provided that I know the pinouts?
I'm guessing probably not, because the number of windings between the different pins will be different (which will probably result in a very different HV output). I do have a few junk boards at my grandma's house, though. One of them is from an old monitor and it has a flyback. May or may not be good, though (got it from a TV shop when they were trying to clean up old stuff).
Still, I'm just curious if this may work or not or if anyone has done it before.

Again, thanks for the help everyone.

Last edited by momaka; 07-08-2011 at 10:42 PM..
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Old 07-08-2011, 10:46 PM   #13
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Testing the HV output of the flyback will achieve nothing. The flyback can provide valid HV at the suction cup even if it arcs internally somewhere.

And no, you cannot use a different flyback. About half the power supplies of the monitor are derived from it.
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Old 05-10-2012, 12:57 AM   #14
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Cool Re: I need help fixing a Sony GDM-FW900 24 CRT

And look what we have here:
http://www.badcaps.net/forum/attachm...1&d=1336629435
http://www.badcaps.net/forum/attachm...1&d=1336629435
Yes, sirs - that would be a brand-spanking new flyback from Sony ^_^ .

In the end, I figured why not fix the monitor. After all, 22" monitors around here still cost around $100-120 - and that's for LCD technology. I want GOOD colors.
----
Now the D-board is out and ready to receive the replacement, but I have a few questions that I hope some of you gurus won't mind answering.

1) Do spark-gaps go bad?
Reason I ask is because there's several of them on the D-board, 1 of which used to arc every time the monitor tried to start with the old (dead?) flyback. It looks slightly dull and possibly carbonized on the inside. Would that spark-gap have to be replaced? Would it (eventually) kill my new flyback if I left it as is, even if it doesn't arc? As far as I checked it, it's not shorted or anything like that.

2) How should I proceed about adjusting the monitor with the new flyback and what equipment do I need?
I'm thinking just to see at what position are the Screen and Focus knobs on the old flyback and then position the Screen and Focus knobs the same way on the new flyback. After that, maybe fine-tune the CRT monitor once it's running?? Or am I completely on the wrong track?
Also, would I have to adjust the HV going to the tube?
I only have a crappy multimeter, so not much for test equipment. I have measured 1.5 KV with it before, and it didn't die.

Sorry if these are very noobish and stupid questions. I just have never fixed a CRT monitor with that kind of issue before, and since this is pretty cool monitor IMO, I would like to try and not screw it up (especially after getting the new flyback - it ain't cheap, that's for sure).

By the way, I got the flyback from PartStore.com. At first, I didn't believe that it would come since it was out of stock and I didn't get any order confirmation emails on my order at all. Was expecting to get my money returned soon and be told that it's not available. Still, I waited, though. 3 week later, the package shows up. The pins were quite bent due to somewhat inadequate packaging, but at least none are broken and the core seems okay.
Attached Images
File Type: jpg new GDM-FW900 flyback (2).jpg (85.6 KB, 33 views)
File Type: jpg new GDM-FW900 flyback (1).jpg (257.9 KB, 35 views)

Last edited by momaka; 05-10-2012 at 01:06 AM..
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Old 05-10-2012, 01:04 AM   #15
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

I am not sure if you have service manual for this monitor model or not, but you do need high voltage DC meter to correctly set the high voltage output, if is too high, you will get X-ray radiation from the CRT. So be care real careful.
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Old 05-10-2012, 11:58 PM   #16
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Thanks for the replay, budm.
Yes, I do have the service manual. Link is actually in post #1, I just mistakenly happened to call it a "schematic".

Anyways, I looked at the service manual again today and it does say that the HV tube voltage should be checked if the flyback is replaced. Unfortunately, I don't have a high-voltage DC meter, and I don't know anyone who has either.

The new flyback is genuine Sony part. Can there really be that much of a difference in the HV tube voltage? The HV tube voltage is adjusted with a potentiometer, but the potentiometer is covered in epoxy, so I (and no one else for that matter) has made any adjustments to it.

The only 2 checks I can perform to check the HV are
1) to measure the output voltage for the HV_DET power supply (cathode of D912) - should be 29V or more.
2) Put 34V on the cathode of D912 and check that the HV tube voltage is 100V or less.
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Old 05-11-2012, 12:07 AM   #17
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

How does the manual tell you how to adjust the high voltage, they may have put the test point for making the adjustment without using the High voltage DC meter, you should follow the manual, X-RAY radiation is not some thing you will want to take it lightly, there should be warning in the service manual about it. I do not have the high voltage probe anymore since I have not worked on CRT in the last 8 years. I did fix a lot of old TVs that run all tubes, that was in the 73, long time ago. I still have my CRT De-gaussing coil though. if the high voltage too hing it may affect the Convergence alignment also, the CRT is the TRINITRON right, make sure to seat that high voltage cup correctly, I believe it may have dual high voltage pin on it. It will arc real bad if you do not install it right.

Last edited by budm; 05-11-2012 at 12:10 AM..
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Old 05-11-2012, 06:24 PM   #18
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

Well, now that I read twice over the Safety Related Adjustments (see attached picture below), it says just to "check" those certain items as a safety "precaution". What I understand from this is that since I'm only replacing the flyback, no adjustments should be necessary to the HV tube voltage unless it's outside of the specification. Also, I don't see any test points for the HV tube voltage.

I think I'll just perform the HV Regulator circuit and HV Protector circuit checks, minus measuring the HV tube voltage. X-rays be damned!
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Old 05-11-2012, 07:40 PM   #19
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

It is right there under the High Voltage regulation
Step #1 Enter blah, blah, blah, check the high voltage is in specified range, specification: 28,500V +/-100V (28.5 +/-0.1KV).
They assume you do have High voltage probe to do the verification, you can also see that it is pretty precise to be within 100V of 28,000V! That is tight tolerance.
I hope you will still want to have kids in the future, LOL.
or get one of this:
http://www.ebay.com/itm/X-ray-detect...#ht_500wt_1202

Last edited by budm; 05-11-2012 at 08:06 PM..
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Old 05-11-2012, 09:51 PM   #20
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Default Re: I need help fixing a Sony GDM-FW900 24 CRT

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I hope you will still want to have kids in the future, LOL.
Future? What future? Haven't you heard of 2012?

In all seriousness, I still doubt this can be any worse than cell phone usage. Heck, most USB 3G/4G wifi cards come with a warning that you should always keep your body and hands as far away from the device as possible. I bet in a few years from now, someone will eventually come out with a study how bad all of these wireless devices are. (but are they really?)

And what about cigarettes? IMO, that shit is even worse.

I did find this article on eHow, though:
http://www.ehow.com/info_8369667_saf...-monitors.html

Quote:
Originally Posted by eHow
CRT monitors emit electromagnetic radiation, which is harmful to human cells.

Oh noes! Quick! Turn off the lights in your room, turn off your cell phone, and hide under the kitchen table!

Quote:
Originally Posted by eHow
The interior components of a CRT monitor contain voltage.


Seriously? Are the people who write these articles actually getting paid? This is something I could write when I was 5.

Back O/T - I think I'll just "risk" it and replace the flyback without doing adjustments. The whole back of the CRT is shielded. And it's not like I'm doing some kind of a hack job - I'll be replacing a genuine Sony part with a genuine Sony part. *Should* be fine IMO. It's not like I'll spend more than a few hours in front of that monitor either.

Last edited by momaka; 05-11-2012 at 09:58 PM..
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