Lenovo li2341twf Monitor - Short / No Power? (Repair Help)

Discussion in 'The Projects Forum' started by mikey32230, Aug 21, 2015.

  1. mikey32230

    Thread Starter New Member

    Aug 21, 2015
    Hello, so I bought a Lenovo li2341twf touch screen monitor about a year ago. Upon opening and first installation, it powered on for only a few seconds and then turned back off. We ordered a replacement, but lenovo never wanted the original monitor back.. so now I have this broken one laying around and I would love to be able to repair it.

    Observations of what's wrong:
    When I plug power into the monitor (19V power supply), the switchboard LEDs power on but the buttons are non-functional. A capacitor near the IC (as well as the IC) gets extremely hot.

    The P/N on the IC is:

    I have no idea where to find schematics for any parts in this monitor, I have spent a lot of time searching.

    2) I took off the plastic connector piece (switchboard side) that houses the 6 colored wires. I measured DCV for each pin (red probe on pin, black probe to GND (metal chassis)). This is what the voltages were:

    Yellow 2.8-2.9V
    Green 1.9-2.0V
    Black 1.9-2.0V
    Brown 0V
    Grey 0V
    Red 2.3V

    *Brown and Grey seem to a return for power on its way to the mainboard / power supply. A circuit seems to complete itself when both yellow and brown are connected, thats when all the LEDs turn on. I also took these voltages:

    Between Yellow & Gray 0.7V
    Between Yellow & Brown 3.0V

    3) Resistance between 2 legs of C702 = 2.6 Ohms
    Voltage between 2 legs of C702 = 2.94Volts
    ***I desoldered C702 and I still get 2.6-2.8 resistance between those solder pads.

    Troubleshooting thus far:
    ***I have been following the guidance of Budm from this thread, but he has recently gone into surgery for cancer and wont be able to provide any help for a while.***

    This is the last thing Budm has said to me:

    "Since that cap (C702) is more likely to be the Filter cap for VCC of that IC, unless the there is anything else that are connected in parallel with that C702, then the only left will be that IC is shorted. We need the spec of the IC to see which pin is the VCC pin, or you can remove the IC and replace it."

  2. ian field

    Distinguished Member

    Oct 27, 2012

    With brand new equipment - dodgy RoHS solder must be the prime suspect.

    Get a jeweller's loupe and a good desk lamp and search in minute detail for tiny hairline fractures in the soldering.

    The front panel micro is probably sensing that a system function isn't initialising and shutting down as a safety feature.