Author Topic: Lenovo Display ThinkVision LT3053p Repair  (Read 297 times)

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Offline Nebukad

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Lenovo Display ThinkVision LT3053p Repair
« on: October 01, 2019, 01:45:40 pm »
Hi all,

I'm trying to repair a Lenovo 30" monitor from 2014.
The initial issue was, that it would not detect any signal from the DP input anymore, but would instead go to "power saving" and switch off.

While diagnosing this issue, at some point the LED started flashing (instead of staying solid orange to signalize standby).

I checked the PSU, which is completely fine. On the Digital board I found a voltage rail, that was doing a lot of funny stuff. It stayed between 1.65 and 1.80 Volts most of the time, but it started dropping to 0 from time to time.

This rails is created by an LDO (Sot23-5 package) from a 3V3 rail, see picture attached. That IC gets crazy hot (>100 °C) after some seconds.

I got the set to work by supplying 1.85 V from an external supply to that rails. It works with every input except DP. When I plug in DP source, something draws up to 1 A from that ~1.8 V rail and still, it is not detecting the input.

My theory now is, that something in the DP-input circuit (which is part of the main ASIC) is broken and draws excess when activated. This has lead to a malfunction of the LDO.

My plan is now to replace that LDO and never plug anything into the DP input ever again.

Does anyone know that LDO IC (U707)? It's in an SOT23-5 package, Pins 1 and 3 are 3V3 (one will be Vin, the other some kind of enable signal), Pin 5 is the output (~1.8V) and Pin 4 is connected to a feedback network (30 k from Out to FB, 20 k from FB to GND). The Marking on the chip says 91410.

Of course I could just retrofit any other LDO and change the resistor network, but I would like to get an exact replacement, and I would like to know the exact voltage, that the rail should be at.

Any help would be greatly apprectiated!
 


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