Samsung SyncMaster LD220HD HDTV/Monitor - no power on

[oddbodd]

Hi Guys,

I've searched for info on this model, but there doesn't seem to be much... even here!

I've repaired a couple of LCD monitors before, but the history of this one is unknown. All I know is that it doesn't power on.

I've attached pics of the power board, which is marked with model number IP-55155B.

I think that I might be imagining it, but the side of the cap C110 might be bulging ever so slightly, although it doesn't look like it in the pic. Is this likely to be the problem? [It's a 1000uf 10v 105c Rubycon ZLH]

Thanks in advance for any help.

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

Any suggestions?

[budm]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

So there is no DC output at all, I.E. 5V? What DC voltage do you get on that large filter cap in the primary side?

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

I've not had time to test anything yet, and wasn't even sure where to start, to be honest. I am a novice at this, although I'm OK at soldering etc.

Are you referring to the large Samyoung NFC 120uF 450V cap [C105]?

Also I've only got a very old analogue multimeter at the moment.

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

I've now got a cheapo digital multimeter.

Should I measure ~5V DC across the pins of the largest cap?

[solarpeter]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

I don't want to hijack your thread but my problem relates to the same model of Syncmaster, (220HD) so maybe it belongs here?
Interestingly I see we have slightly different power boards.
My monitor boots up OK but pressing the source or menu button usually causes the image to break down in a random set of wavy stripes across the screen. The effect of the fault is to scramble the screen image and lock up from any further inputs. Only disconnecting from power allows the monitor to reboot to an image and even then this is often still scrambled.
Like the OP, there is no obvious damage to the power board capacitors but I suspect the display board is crashing due to an unstable power feed from the PSU board?? Do you have any suggestions of possible causes and remedies to try. I am a competent solderer and have already tried replacing the two 1000uF caps as I had some spare.
Is this 'system crash' type fault likely to be related the the power board, or am I barking up the wrong tree?

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

So there is no DC output at all, I.E. 5V? What DC voltage do you get on that large filter cap in the primary side?

Well, I've finally got back to this.

The large cap sparked with a loud crack, when I accidentally discharged it. I guess it's OK!

I also replaced the 2 ZLH 10v 1000uF caps at C110 AND C111.

Still no signs of life, so what should I test next, please? [I don't have an ESR meter]

Thanks

[newtothis]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

can you give us a close up picture of the connectors on the PSU please

[budm]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

Un-solder one end of the F301 and lift that end off the board to see if you will get any DC voltage at the connector that goes to the logic board. You can see the voltage labels at the connector. You can run the power supply board without having it connected to the logic board.

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

can you give us a close up picture of the connectors on the PSU please

These connectors?

[newtothis]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

Can you go across those pins from 1 to 9 and check voltages...

Also follow budm's advice

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

OK, thanks. I'll try tomorrow.

BTW, what setting should I use on my DT830B multimeter, to safely discharge that big cap?

[newtothis]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

I just use a 12Kohm resistor across the contacts

Never done it with a multimeter but sure its possible, someone will confirm this

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

Can you go across those pins from 1 to 9 and check voltages...

Also follow budm's advice

OK, this morning, I have desoldered one pin of F301, powered up the board, and taken the following voltage readings...

The big cap reads 336v
F301 disconnected [if I'm testing it correctly] 0.0 to 0.01 on setting 20 DCV
The voltages across the the connector pins...
1 [B-DIM] 0.0
2 [15V] 13.5 to 14.5 unstable
3 GND
4 GND
5 GND
6 [5.2V] 5.0 to 5.2 unstable
7 [5.2V] 5.0 to 5.2 unstable
8 [DCR] 0.0
9 [ON/OFF] 0.0

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

Update to above post...

F301 [4A fuse] removed from board and tested OK.

Resoldered on board and connectors retested. Results as above except...

2 [15V] 14.3 to 14.6 unstable

[budm]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

I have the fuse lifted up to isolate the inverter circuit from the power supply to see if you will get the DC ob the power supply back and to see if you can turn the monitor on and off when you have the main board connected to the power supply board, if you do have all he voltages and still no power LED (fuse still not connected) then you have problem in the main (logic) board

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

In that case, should I desolder the fuse again, reassemble everything, power up the monitor and see if the LED lights up?

[budm]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

Only if you do not see any voltage as shown on post 14.

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

I'm not sure what you mean. Those voltages in post 14 are without the fuse in circuit.

[oddbodd]

Re: Samsung SyncMaster LD220HD HDTV/Monitor - no power on

Is it safe to power up with the fuse out of circuit?