1602 Troubleshoot

I soldered the pin headers in the front side of the display and when I removed them to solder to the back side,the back side got damaged and I don't know which connection is broken between the solder pads and the very thin copper wires on the back.The Vss,Vdd,V0,A,K connector is working because I've tested them,but when I hook it up to an arduino nano accordingly to the "Hello World",the upper line is lighting(no characters just a line) and the other not, even if I disconnect the RS,RW,E,D4,D5,D6,D7,it remains the same. Does anyone know a solution to debug which pin is not connected(broken)or I should throw it into the trash?

Time to chuck it in the bin as breaking one of the connections along the top row should not take out the second line, something lower on the pc board was damaged.

It's not worth your time at the average $3 replacement cost unless you are skilled with a soldering iron and sharp instruments...

SmileXS4: I soldered the pin headers in the front side of the display and when I removed them to solder to the back side,the back side got damaged and I don't know which connection is broken between the solder pads and the very thin copper wires on the back.The Vss,Vdd,V0,A,K connector is working because I've tested them,but when I hook it up to an arduino nano accordingly to the "Hello World",the upper line is lighting(no characters just a line) and the other not, even if I disconnect the RS,RW,E,D4,D5,D6,D7,it remains the same. Does anyone know a solution to debug which pin is not connected(broken)or I should throw it into the trash?

I would suggest that you replace it. The time and money to repair this one would be more than the cost of purchasing a replacement.

Thanks for the answers!

I wouldn't throw it away yet. Certainly not before you get a new one up and running.

Your symptoms, "the upper line is lighting(no characters just a line) and the other not", have been described here hundreds of times and the problem has usually been found in the implementation not the display.

A few good photos of your soldering and of your connected circuit will help us determine if your display is really defective. We also need a copy of your program code.

Don

Thank you for the reply! Here are some pictures about the display.It looks really ugly,but as I said Vss,Vdd,V0,A,K pins are OK. The code is taken from here: https://www.arduino.cc/en/Tutorial/HelloWorld |500x281|500x281|500x281|281x500

SmileXS4: Thank you for the reply! Here are some pictures about the display.It looks really ugly,but as I said Vss,Vdd,V0,A,K pins are OK. The code is taken from here: https://www.arduino.cc/en/Tutorial/HelloWorld |500x281|500x281|500x281|281x500

A suggestion.

learn how to solder. Practice on broken PCB board or protoboard

or find someone who does know how to solder and pay them to do it.

I still think it is time to throw it in the bin.

The soldering was not a problem,but the unsoldering of the pins without soldering wick,then soldering back the cables was...

SmileXS4: The soldering was not a problem,but the unsoldering of the pins without soldering wick,then soldering back the cables was...

To me, it looks like soldering was big problem. It looks like heat was applied to the side of the PCB where the wires are coated and that too much solder was used. The black on the side of the PCB with the insulated wires indicates that soldering was done on that side and no heat should be applied to that side.

If the wires were solid core vs stranded then it should have been pretty easy to solder, desolder and re-solder again even without using any type of solder wick. Honestly, I don't consider soldering wick that useful. In my 40+ years of soldering, I have probably used soldering wick no more than a handful of times. Now a desoldering iron on the other hand that uses a vacuum bulb, that is quite useful. But in this case, it wouldn't really be necessary since each wire could easily be dealt with separately.

Here's a few tips for soldering wires like that. First question I'd ask is what type of soldering iron are you using? Is it one with a small/smallish pointy tip? If it is a larger one with a chisel then stop and get a new solder iron.

What type of solder are you using? you want to use a very small diameter rosin core solder. For things like that, I use solder that is about 1mm in diameter. Using a large diameter solder makes it very difficult to avoid using too much.

Having a "helping hands soldering station" type of device to hold the PCB for you is very useful and makes things much easier. If you don't have one, I'd suggest that you get one.

For soldering wires like that: Strip the coating off the wires for 4 mm or so. They need to be long enough so that they stick up beyond the solder applied and can be trimmed off after soldering is complete. Poke the bare wire in to the PCB hole through up to the coating and then only apply heat and solder to the side with the wire poking out not the side with the insulation. Never apply heat or solder to side with the insulation. Don't go overboard with the solder, and as heat is applied you may have to push the wire in a bit more as the coating melts back.

For desoldering wires like that with nothing but soldering iron: apply heat to the wire side and gently pull the wire from the coating side as the solder melts. After the wire(s) is removed, you can generally heat up the hole a bit (not too much or too long) to remelt the solder and push off the excess with the soldering iron if there is a blob remaining and/or wipe it with a wet cloth.

To resolder, heat up the hole (which probably is likely full of solder) and poke the wire through while the solder is melted. Touch up with a small amount of solder.

Alternatively, using a 16 pin header is useful if using a breadboard as it allows plugging the lcd into the breadboard which then allows easier wiring to other components.

--- bill

Thank you very much for the useful informations!However I soldered a pin header to the LCD.The problem is that it was soldered incorrectly at the beginning,around one year past,when I could not solder,and I had a bad soldering iron. The reason why a posted is to see if anybody can diagnostize the reason of the problem-why just the upper light is lighting,then try to repair the connection at the corresponding connector.

SmileXS4:
Thank you very much for the useful informations!However I soldered a pin header to the LCD.The problem is that it was soldered incorrectly at the beginning,around one year past,when I could not solder,and I had a bad soldering iron.
The reason why a posted is to see if anybody can diagnostize the reason of the problem-why just the upper light is lighting,then try to repair the connection at the corresponding connector.

I have nearly 45 years as an Electrical Engineer. I have many tools acquired over the years to fix items such as this. I have made many of my own. I use my iPod’s camera as a video magnifier. I would use my micro probes made from diabetic syringe and needles. the needles are very small. the syringe body acts as any insulator. A length of silver wire-wrap wire is passed into the needle through the syringe body and soldered to the inside of the needle. I use these as micro-probes with a homebrew oscilloscope. I probably could fix this purely as a challenge. To show that it can be done. It is impossible to diagnose the display at a distance.

If I were to attempt fixing this display my first step would be to remove the wires and clean up as best as I could the solder pads. the wires and solder are obscuring the abilities to determine the damage. I would use a vacuum sucker to remove the solder. I have an surface mount rework station with a re-flow oven. I can dial in the temperature that I need for the job at hand. Once all the wires and solder are removed, clean the area with flux cleaner or 100 % ethyl alcohol. Then I would place the PCB on a scanner and scan the back side of the board with 600 dpi. this will allow me to see the traces and the small defects. depending on the trace or traces that need repair, I would probably go with solder paste and bare silver wire-wrap wire. This silver wire-wrap wire is about the width of a human hair. very small but very conductive. Solder the solder paste with the hot air rework pencil.

This entire repair takes two thing people do not want to spend, time and money.

I would recommend that you find silicon insulated hook up wire. I have both stranded and solid.
Silicon insulated hookup wire it a pleasure to work with.

My cousin is a Veterinarian with his own clinic. Him and I have x-ray PCB boards to find the traces.
Rare occurrence when the item really needs to be repaired and a replacement is not available or the replacement is cost prohibitive.

In order to answer your question we would have to know the schematic of the board to see would the LCD display connects to the controller. There is no “one size fits all” when it comes to electronics. A logic analyzer or oscilloscope would probably be needed.

Just a quick update:after 4 months,I tried again to do something with the display,started to scartch up the broken connections and soldered cables in their place.After 30min of soldering,I tested it,and believe it or not,it works!Without special tools,by just a bit of patience I repaired it.Thanks for the repairing tips and ideas again and for the motivation!



Thanks for the update. As you can see, it's pretty hard to kill those devices.

Don