JP4 is on the output of the 3.3 volt regulator so the fault is that something on the 3,3 volt rail is taking too much current. Try to follow the track of the 3.3 volt line looking for shorts to some other track . You could measure the resistance from this track (TP23 is a suitable point to connect to it.) to ground (power supply negative.) You could try unplugging the LCD connector as this is connected to the 3.3 volt rail.

Les.

 

If it is melting the solder then it should be hot enough. I should be the last person to criticize and give advice on soldering. My soldering is not the best either but I think mainly do to shaky hands.

There are a couple of main things to know when soldering. Make sure you have a clean and properly tinned tip. The tip of the soldering iron should be the first to be applied to the joint and the last thing to be removed. The idea is to have the joint melt the solder not the iron.

If you just melt the solder on to the joint, this is what is known as a "cold solder joint". A solder joint should be nice and shiny and sort of conform to what you are soldering. A dull blob is a bad thing. It should be removed and try again,

There are many videos on soldering. Try to find a good one and watch it before you try your next project.

OK thanks anyway
I took your advice (@MrChips and @spinnaker) and changed my iron tip with new one
Also resoldered every joint which was not OK
I know it's not perfect but at least I tried

 

JP4 is on the output of the 3.3 volt regulator so the fault is that something on the 3,3 volt rail is taking too much current. Try to follow the track of the 3.3 volt line looking for shorts to some other track . You could measure the resistance from this track (TP23 is a suitable point to connect to it.) to ground (power supply negative.) You could try unplugging the LCD connector as this is connected to the 3.3 volt rail.

Les.

Thanks for your help
After resoldering and washing extra flux and possible dirt by ethyl alcohol and wipe and clean it, the problem vanished
Actually around 40 minutes it worked flawlessly with 1KHz test signal and no overheating or LCD failure took place
So I must say the poor soldering was the reason

Thanks everyone for valuable share of information and help
I will take soldering advices for other projects

 

Two problems solved in two days! We're on a roll.

 

Two problems solved in two days! We're on a roll.

I am curious about something, despite the fact that device works now, what if someone wants to change U5 with higher current capable voltage regulator, because it seems U5 is still hot
It consumes 90-110 miliamps which will reduce device life and reliability

 

I woke up this morning at 10.00 and found that with the help of the members here you've finally found the fault. Congrats to all.

Any way I have taken a few shots just to show how my scope is still doing.


I managed to get a small 2 pin plug for the power but my pos and neg lines are reversed (Black is positive and red id negative).

Allen

 

I am curious about something, despite the fact that device works now, what if someone wants to change U5 with higher current capable voltage regulator, because it seems U5 is still hot
It consumes 90-110 miliamps which will reduce device life and reliability

I measured the current consumption of my scope and it was almost same as yours 109.4mA.

I checked the datasheet of LM78L05 and it has a typical max of 140mA, so running at 110 mA should be fine. But if you must change it, I'd recommend the L4931 series of regulators. It has a normal output of 250mA and Max at 300mA. see datasheet attached.

To use 7805 in TO220 package it would be too big and you wouldnt be able to insert the LCD on top of the PCB; unless you bend the regulator and it would make a mess oout of the PCB.

Another way to to make or buy a small heatsink for the 78L05 To92 like this.... with the top part saw off.

 

I measured the current consumption of my scope and it was almost same as yours 109.4mA.

I checked the datasheet of LM78L05 and it has a typical max of 140mA, so running at 110 mA should be fine. But if you must change it, I'd recommend the L4931 series of regulators. It has a normal output of 250mA and Max at 300mA. see datasheet attached.

To use 7805 in TO220 package it would be too big and you wouldnt be able to insert the LCD on top of the PCB; unless you bend the regulator and it would make a mess oout of the PCB.

Another way to to make or buy a small heatsink for the 78L05 To92 like this.... with the top part saw off.

View attachment 166802

Thanks man
In any case if there is any problem regarding 78L05 I will try one of your solutions
Good luck