Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

[solarpeter]

I have an unstable Samsung Syncmaster 220HD which boots up OK but pressing the source or menu button usually causes the image to break down in a random set of horizontal 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.
There is no obvious physical damage to the power board capacitors but I am guessing 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 and have some 680uF and 820uF caps on order.
Is this 'system crash' type fault likely to be related the the power board, or am I barking up the wrong tree? I would really appreciate any pointers!

[solarpeter]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

Further to the above, I have pulled the power board out and powered it up to check the voltages on the 5.2V and 13V outputs. I see 330V on the large capacitor, dropping rapidly when the board is powered down.
There is no load as the board is not connected and I am getting 5.24V and 12.83V respectively. Is the variance on the 13V line of any significance to this instability problem?

[tom66]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

Those voltages are fine.
One thing to try would be service reset - does this TV/monitor have a remote?

[solarpeter]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

Thank you for your response. My daughter brought this TV to me for fixing but forgot the remote. Is there a way of resetting without it or do I need her to get it sent here?

[tibimakai]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

Samsung TVs require a remote to reset them.

[solarpeter]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

Many thanks to the previous contributors.
I now have the remote but can no longer get the TV to boot to a usable display, it is producing the scrambled image every time now and accepting no inputs, so resetting to factory defaults is not achievable.
I have now started to suspect the fault is on the main board as the voltages coming from the supply look to be within the expected range.
Using Retiredcaps excellent guide to checking voltage regulators I have checked the two regulators adjacent to the power feed on the main board.
The first is marked 7M809A gives me 13.7V on pin1, 0V pin2 and 8.96V on pin3, so this looks OK.
The next chip is marked 1117 0914AG . Measuring between ground and each pin is giving me 0.62V, 1.87V and 3.27V on pins 1 to 3 respectively.
Am I right in thinking this doesn't look good - Can anybody suggest what readings I should expect from such a chip?

[solarpeter]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

Having taken readings from the two 1117 0914DG chips on the other side of the board I realise that my earlier question is probably unanswerable. The two identical chips on the top face of the board are giving (pin to ground):
Chip 1: 0V, 1.23V and 3.26V
Chip2 : 3.7V, 4.98V and 8.9V

Maybe I should try replacing the main board?

[budm]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

Chip 1: 0V, 1.23V and 3.26V (0 +1.25 = 1.25 V +/-2%)
Chip2 : 3.7V, 4.98V and 8.9V (3.7 + 1.25 = 4.95V +/-2%)

0.62V, 1.87V and 3.27V (1.25 + .62 = 1.87V +/-2%)

They are OK.

[selldoor]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

I was just about to say that - if you read to the bottom of retiredcaps guide
budm mentions the caps attached to the regulators for stability.
We have had quite a few cases where the VRs have been good but the
caps bad.

[solarpeter]

Re: Possible causes for Samsung Syncmaster 220HD image 'scrambling'?

As an update and a reference for others with similar problems in the future-

I managed to get a second hand main board, which now works, proving the fault lay somewhere on that board rather then the PSU that I initially suspected.

Unfortunately that isn't the end of the story as my 'new' board seems unable to detect the HD channels and creates frequent lock-ups where both the remote and manual inputs are ignored until a reboot.

Nevertheless I have a working TV, which is massive progress. Many thanks to those who have assisted me, I have learned a lot from this.