1. Home
  2. Electronics Repair
  3. Samsung LCD monitor: screen blanks after 1 second

Samsung LCD monitor: screen blanks after 1 second

This is a SyncMaster 2233SW that worked fine for years, but then the image disappeared. Further investigation showed that the image would display for just a second or so after power-up or after switching inputs. So: looks like classic defective-power-supply problem, probably resulting from crappy electrolytic capacitors.

When I took it apart I found that there were bulging caps and a partially discolored PC board.

Since the PC board itself showed signs of overheating, I thought it better to look for a replacement power-supply module than to simply replace the electrolytics on the old one. I bought one on eBay that was described as having come from a monitor with a cracked screen. It had no sign of bulging capacitors or overheating, but it did not solve the problem. The seller refunded my money and did not want the apparently defective unit returned, so I got a set of replacement capacitors for that one. BUT that has still not solved the problem: with two different computers, whether I use the analog or the digital input, there is an image for just one second or so. AND I do not see any trace of an image when I shine a light onto the screen either.

I cannot find a service manual for this monitor -- at least not without sending money to a person or business of unknown integrity.

Where do I go from here?

Perce

Reply to
Percival P. Cassidy
Loading thread data ...

There's typically a sensor that shuts down the backlight if it senses a problem with the backlight. I fixed one of those with a new transformer, but the first one of those shipped to me with an open secondary. Second one worked.

I "fixed" a second monitor by disabling the protection chip. I wouldn't recommend that to anyone else tho...

If the backlight is on a different board, you may find something there. It's possible that the new board had the same failure mode.

Normally, you'd expect the image to stay up even if the backlight turns off, but who knows what the designer decided on that model.

Had one monitor that had a bad cap in the 5V. Supply. The spikes on the 5V caused the controller chip to malfunction and lock up.

Probe around with a digital storage scope to see what happens on power up.

Reply to
mike

I neither own nor have access to any kind of scope.

The power module has connectors for four 2-wire leads that run to one vertical edge of the screen, and another connector from which a multi-conductor lead (more than 2 conductors, but I don't recall how many, and it's not open at the moment for me to look) going to the bottom edge of the screen (perhaps to the control buttons?). There is another module that has the analog and digital signal connectors, a multi-connector lead from the power module, and a shielded multi-connector lead going to the top edge of the screen.

Perce

Reply to
Percival P. Cassidy

that makes it difficult

I have seen descriptions of replacing the CFL backlights with white LED strips. That would make a nice project.

Mark

Reply to
makolber

Sadly - heat discoloured PCBs isn't as rare as it ought to be.

The trick is to make a judgment as to whether there is potentially a fire risk. In any case - a replacement from the original source will probably go the same way.

If the problem is on the CCFL inverter board - a company called HR in Spain does pattern spares.

They were originally well known for high quality pattern replacement horizontal output transformers for CRT displays.

Reply to
Ian Field

I don't want to put much more money or time into this project: I already have a replacement for our own use but would rather keep it as a spare or donate a working monitor to the thrift store/charity shop (whichever term you use where you live) than simply trash it.

Perce

Reply to
Percival P. Cassidy

On Thursday, October 22, 2015 at 3:05:38 PM UTC-7, Percival P. Cassidy wrot e:

Older LCD monitors use CCFL (Cold Cathode Fluorescent Lamps) for backlighti ng and these wear out like any other lamp. Capacitors also go bad FREQUENTL Y. There are 'kits' ($15 to $20) to convert CCFL to LED backlighting and I have successfully converted several monitors to LED but it requires above a verage knowledge. The panel gets disassembled down to individual layers in the backlighting, possible mechanical mods to accommodate the new power mod ule and getting the 12-30 Volt power source into the new power module.

The monitors I did this to are in rack mount drawers with keyboard and trac k pad so the time was worth it to salvage these expensive units. For home u se that's your call and with 24" units on sale for $100 it may not be worth the time unless you want the 'education'.

Reply to
stratus46

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.