Walked some trash to the rubbish bins and saw a 17inch Acer AL1721 flat panel screen (for a PC)  dumped at the bins. Don’t get to see many flat panels. Seemed to not have a cracked screen so I just had to take this back home.

At home I used a spare 5AMP 12 V DC power pack (centre positive) I had similar to what is used for CCTV cameras and it kind of worked but screen blanked out when DC plug was wiggled.

This had to be easy to fix so I unscrewed the screen back (4 x small black screws and 4 x larger plated screws under the stand mount covers) and then popped off the front bezel screen surround and removed the back (take care to un-plug the screen controls plug).

The PSU is slightly different from other screens and is an all-in one with the backlight high volt supply and the logic supply together on the same PCB. The fault was easy to find though – there is a choke on the DC input on the PCB and that had a visible dry joint.  I can only assume some contamination on the pin when it was soldered at the factory.

Dry Joint on PSU PCB

I solder-sucked and scraped the pin with a knife edge to the copper on the pin and then re-soldered. There was also a 470uF 16VDC electrolytic that was swollen (HERMEI brand) though my ESR meter did not show a problem. I replaced it anyway given it was swollen (the spare capacitor was cannibalized from the power section of an old CDROM drive so this fix cost me nothing).

Swollen Capacitor on AL 1721 PSU PCB

It works; stable at 1280×1024 75Hz on a GNU/Linux server running Ubuntu 10.10 with on-board ATI Radeon 3000 graphics (ASUS M4A78LT-M LE motherboard).