Samsung Syncmaster 731N - No backlight

[lti]

Re: Samsung Syncmaster 731N - No backlight

No, I don't. Those pins are actually being pulled low (connected to ground) by the OZ9938, even during the second of activity on pins 12 and 13. When the monitor is unplugged, the outputs float (no connection to either ground or VDDA).

[lti]

Re: Samsung Syncmaster 731N - No backlight

I think the only way I will ever get anywhere is if I find a service manual (or at least a parts list) and a way to remove components that are glued down. I damaged the board when I tried to remove the original OZ9938. Every surface mount component is glued down with that horrible red glue that is almost impossible to remove.

Does anyone know where I can get a replacement power supply? I would prefer not to use the universal inverter from eBay. I want to use this monitor in a multiple monitor setup, so I want something reliable.

[lti]

Re: Samsung Syncmaster 731N - No backlight

I found the service manual. The Samsung Syncmaster 720N uses the same power supply, so I'm using its service manual. I got it from ElektroTanya. The troubleshooting section says that IC501 (the OZ9938) is bad, but I already replaced it and the symptoms didn't change. There was no signal on pins 1 and 15 of the original chip, and there still isn't any signal with the new chip.

The troubleshooting chart is messed up as well. It looks like it was written by the person who did this.

Of course, I can't read the component values on the schematic.

[lti]

Re: Samsung Syncmaster 731N - No backlight

I got a new power supply for this monitor. It works now. The old power supply would have been nearly impossible to repair due to the red glue.

[lti]

Re: Samsung Syncmaster 731N - No backlight

Now this monitor has the front panel button issue described in these threads:
https://www.badcaps.net/forum/showthread.php?t=22450
https://www.badcaps.net/forum/showthread.php?t=12496

In my case, the brightness increased to 100% and all the buttons stopped responding. It's too bright to use, so I have to use my laptop's horrible built-in display.

According to the schematic, the components in this section are SW903, SW904, and R902 on the front panel board and RP102 and R161 on the main board. I'll check those and possibly replace the buttons. If I replace the buttons, I might as well replace the 1.8V regulator that is known to fail so I don't have to take it apart a third time.

[lti]

Re: Samsung Syncmaster 731N - No backlight

I fixed it.

I started by measuring the resistance between ground and pins 2, 3, and 4 of CN901. The resistance between pin 3 and ground was fluctuating between 2-4MΩ, while the resistance between the other pins and ground was too high for my multimeter to read. Removing R902 made the resistance go infinite like the other pins, meaning that SW903 was bad. Connecting the button board with SW903 disconnected did not make the problem appear.

If anyone else has this problem (menu opens and won't close, brightness increases, or auto adjust runs constantly), these are compatible replacement buttons:
http://www.digikey.com/product-detai...099-ND/1146757
http://www.digikey.com/product-detai...089-ND/1146803
The second one has higher operating force. I don't know which is closest to the original. Replace all six buttons.

[lti]

Re: Samsung Syncmaster 731N - No backlight

I received the replacement buttons today. The actuator height is a little shorter than the original switches, but it was the largest I could find. They are more difficult to press when the monitor is assembled because of this, but I won't need to use them very often. Also, the version with higher operating force will be closer to the original switches.