My first TFT repair - Nec LCD1703M

[goodpsusearch]

As you can see there are 3 Hermei caps bad.

I am wondering if the power supplies of TFT displays in general use same esr caps as computer power supplies.

Then I suppose I could replace the 2x 1000uF 16V Hermei caps with 2x Rubycon YXF 1000uF 16V or Nichicon HD....

And another thing that I need some help is about the 470uF 16V Hermei caps. Will it hurt if I replace them with 1000uF 16V ones?

Thank you very much for your help

[smason]

Re: My first TFT repair - Nec LCD1703M

I'd try to keep the replacement caps close to the original values.
Perhaps Willawake can suggest a supplier in Greece.

What's the symptom? That design looks vaguely familiar.
I'd check the transistors in the inverter section for shorts.

[goodpsusearch]

Re: My first TFT repair - Nec LCD1703M

I haven't connected it on ac yet... I found it some hours ago.

Can you show me the inverter section? I have no experience with tft...

[retiredcaps]

Re: My first TFT repair - Nec LCD1703M

Can you show me the inverter section?

It is the left hand side of the power board where PT201 and PT202 sit. smason is probably talking about Q209 through Q212.

[b700029]

Re: My first TFT repair - Nec LCD1703M

Will it hurt if I replace them with 1000uF 16V ones?

There is no harm in doing that. There are filter caps and rising of capacity can't make trouble in this case.

[momaka]

Re: My first TFT repair - Nec LCD1703M

I am wondering if the power supplies of TFT displays in general use same esr caps as computer power supplies.

They do, more or less.
The only difference is that the power supplies of LCD monitors don't have large toroidal coils on the output rails like PC PSUs do. Therefore, you can actually go with much lower ESR capacitors if needed. I still recommend staying close to the specs of the original capacitors, though. The only exception to this rule is if the original capacitors are rated for 85C - never put 85C caps in a LCD PSU because they just won't last very long.

By the way, make sure to replace all of the caps, not just the few bad ones. The only cap you don't need to replace is the big 400v one on the primary side because those very rarely fail.

[goodpsusearch]

Re: My first TFT repair - Nec LCD1703M

By the way, make sure to replace all of the caps, not just the few bad ones. The only cap you don't need to replace is the big 400v one on the primary side because those very rarely fail.

I wish I could afford replacing all of the capacitors..

Judging from the pcb discoloration, the 4 output caps are the ones that get very hot.

Thank you for your help! I am waiting for replacement caps. I think I'll use Rubycon YXF 16V 1000uF.

[momaka]

Re: My first TFT repair - Nec LCD1703M

I wish I could afford replacing all of the capacitors..

I guess I should have been more specific - replace all of the caps on the PSU only. There's actually only 3 more (1 is the small start-up cap, and the other 2 are the blue ones for the inverter).

Judging from the pcb discoloration, the 4 output caps are the ones that get very hot.

Yes, but the 2 blue ones in the middle of the board (extra filter caps for the inverter input) have also likely taken a beating after the 4 outputs caps failed since they are connected in parallel.

[goodpsusearch]

Re: My first TFT repair - Nec LCD1703M

I guess I should have been more specific - replace all of the caps on the PSU only. There's actually only 3 more (1 is the small start-up cap, and the other 2 are the blue ones for the inverter).

I see 4 extra caps....



Very useful info! What exactly an inverter does, how many volts it takes as an input and how many volts it outputs? Thanks!

[PlainBill]

Re: My first TFT repair - Nec LCD1703M

I see 4 extra caps....



Very useful info! What exactly an inverter does, how many volts it takes as an input and how many volts it outputs? Thanks!

An inverter steps the inverter supply voltage (in this case, probably 12 volts) up to the 700 volts required to light the CCFLs. It also adjusts brightness and protects against broken or aged CCFLs. Datasheets for the inverter controller will give many more details.

PlainBill

[Lumberjack777]

Re: My first TFT repair - Nec LCD1703M

Very useful info! What exactly an inverter does, how many volts it takes as an input and how many volts it outputs? Thanks!

Another thing the inverter does is to change DC to AC. In this case 12v DC would be converted to upwards of 700v AC. The inverter performs the opposite function of a rectifier.

The interesting thing about an LCD power supply/inverter is that it takes the source AC current (120v or 240v) and converts it to DC. Then the inverter section turns around and converts the DC to AC. The frequency of the AC can thereby be specified for the CCFL lamps.

[Rtech]

Re: My first TFT repair - Nec LCD1703M

An Inverter to me,prior to getting into Monitors, was also called a Variable Speed Drive up to 250KW,which was powered by 3 phase mains,and the voltage was changed to DC and then back to AC,via Thyristors.Some of the DC became again 12volts and this was used in the Controller Board to vary the output freqency,so speed could be adjusted from 0-100hertz,therby slowing or speeding up the Motor .This was used in lots of ways for example,Coca Cola used one to vary the speed of the cans going along conveyor belts,use in 'Carbon Black' manufacture,and the one I liked ...to vary the speed of the motor the pulled the coffin through the curtains,and no doubt will be used when its curtains for me.Although they say, that only the good die young,so I have a long way to go...I hope.

[goodpsusearch]

You can't be lucky every time...

I replaced 6 caps...

2xHermei 1000uF 16V LE (General Purpose Low ESR) -> 2xRubycon YXF 1000uF 16V
2xHermei 470uF 16V LT (Lower ESR) -> 2xRubycon YXF 1000uF 16V
2xHermei 150uF 25V LZ (Ultra Low ESR) -> 2x Panasonic FM 220uF 35V

..only to find out that the lcd is broken

Anyway thanks for your help!

I consider it a training session for the next time.

[alexanna]

Re: You can't be lucky every time...

I replaced 6 caps...

2xHermei 1000uF 16V LE (General Purpose Low ESR) -> 2xRubycon YXF 1000uF 16V
2xHermei 470uF 16V LT (Lower ESR) -> 2xRubycon YXF 1000uF 16V
2xHermei 150uF 25V LZ (Ultra Low ESR) -> 2x Panasonic FM 220uF 35V

..only to find out that the lcd is broken

Anyway thanks for your help!

I consider it a training session for the next time.

Ya really gota be realy careful with this stuff,It almost like eating potato chips you can't do just 1!

[Scenic]

Re: My first TFT repair - Nec LCD1703M

i'd still keep it. just wait for another 17" LCD with f*cked up electronics (like some of those Samsungs which always show "out of range" or something) and retrofit the panel into the NEC..

i did something like this a dozen times.. always worked fine if the resolution of both panels is the same..

[goodpsusearch]

Re: My first TFT repair - Nec LCD1703M

i'd still keep it. just wait for another 17" LCD with f*cked up electronics (like some of those Samsungs which always show "out of range" or something) and retrofit the panel into the NEC..

i did something like this a dozen times.. always worked fine if the resolution of both panels is the same..

Is that possible with Nec LCD1703M and Samsung Syncmaster 710V????

(https://www.badcaps.net/forum/showth...843#post264843)

[Rtech]

Re: My first TFT repair - Nec LCD1703M

i have replaced faulty screens with panels from othe rmakes and models with no problem,for example 17" to replace a 17" etc.It can be not a simple as that, but it is worth a try if you have a possible replacement,.

[goodpsusearch]

Re: My first TFT repair - Nec LCD1703M

And how you do it? Is there a step by step guide? I have no experience in this...

[Rtech]

Re: My first TFT repair - Nec LCD1703M

Well, hopefully the whole panel ie the lights and screen are the same dimensions as the original, and the whole unit just replaced.

[goodpsusearch]

Re: My first TFT repair - Nec LCD1703M

This IBM L170 monitor was the panel donor that helped me bring this NEC TFT back to life