Screen turns white after couple of minutes

[farzadlatifeh]

I bought a dso138 kit and soldered it
At first everything was OK but after a couple of minutes LCD turns white, after reset it works perfectly but after some time LCD again turns white, time of LCD getting white decreases as much as I tried to work with it by reseting
I tried test mode but there was no short since LED blinks slowly
I tested voltages and it seems to be good however I used 12V PS instead of 9V. All voltages are seem to be good, all un-stared voltages were OK while some stared were higher than reference which seems to be good since I used higher voltage PS for example L1 voltage was around - 10 instead of - 8
LED blinks twice which is a good news about MCU by the way the LED continue working flawlessly after LCD turning white and there is no overheating component while U4 and U5 are a little bit warm
It seems there is an interference which interrupts LCD
Any idea dears?
Does may resoldering help?

[farzadlatifeh]

Sorry my mistake
U5 is too hot
Now what should I do?

[farzadlatifeh]

And also all 100uF Caps are around 180uF
Why is that?
Any idea?

[farzadlatifeh]

After so many trial and fail finally it works flawlessly
The problem lies behind poor soldering skills and inappropriate PSU
Actually U5 is very sensitive to current consumption, device consume 90-110 miliamps which is around maximum U5 current specification (the bottle neck) so just a few extra miliamps will result in device failure which usually take place with LCD whitening issue because U5 is main feed for +3.3V regulator and this voltage has used in LCD and MCU. So I am going to give you guys some troubleshooting advices as I experienced to solve the case in similar issues since there is no commitment here for people who designed the device unfortunately.
1- First of all be careful about PSU for your device, the device is not high current consumer so using Transformers may result U5 get overheated, the kit has no power source and that is a big problem, usually Transformers have higher voltage than what its stated since maximum load always decrease voltage therefore the stated voltage for transformer actually is under the max load condition and DSO138 never ever use it, so don't go further 9V and 500 miliamps PSU otherwise U5 will burn and check PSU with multimeter despite how much you spend on it or where it has been manufactured
2- be very careful about soldering, this kit is not like anything you did before, so go and watch soldering videos around the web for best result, always clean iron tip and do not try to be fast, an extra hour is better than ruining the device. Be carefull about LCD pins on both main and LCD board. Let joint melt solder not the iron.
3- if U5 get hot first of all disconnect JP4 and then see if overheating is still there or not, if overheating disappeared then there is a problem in +3.3V branch, otherwise the AV+ branch may is shorted, in this case to be sure resolder JP4 and remove L1, if overheating disappeared then it's AV+ branch issue.
4- in case of +3.3V branch issue, Check pin No. 5 of CPL and Sen1, 2 not to be grounded. Check +3.3V pin and GND resistance, there shouldn't be any conductance here otherwise you have short in +3.3V branch, check pins 32,33,34 of LCD on main board since GND and +3.3 branch are close there. Check C15, 16, 17, 18 and 26 for possible short. Check J6 pins. Finally check D3 and R28.
Hope you enjoy the kit, it's a thing anyway.