Repairing a broken lab bench power supply

How I (not) replaced a broken display

Hello everyone!

I had a go today a replacing the broken display of my lab bench power supply. It is a 3 digit 7-segment-display used to show the current voltage provided. A few lines of the second digit are broken, as you can see in the image below: Lab bench power supply with broken screen

Opening up the power supply was really easy. I only had to remove 6 normal screws (no proprietary bullsh*t, I'm looking at you Apple!) to open the case and once inside, just 6 more to get the circuit boards with the displays out. Inside look into a power supply

I then started desoldering the wires connecting the circuit board (with the display) to the main circuit board. Circuit Board in the process of removal from the power supply

After this, I looked around on the web, trying to find a datasheet for the IC on the display, but due to the old age of my power supply, I did not get lucky. So I decided to leave the circuit board and the IC where they were and get started with desoldering the display to remove it from the board and get a replacement part. I grabbed the smallest tip I could find for my soldering iron and my new desolder pump and got to work. Ciruit Board with soldering tip

After at least 20 minutes, I still didn't manage to remove the screen from the PCB (printed circuit board, if you are wondering). So I gave up for now. I resoldered all the connections I just spend way too much time on removing and then added all the wires back to connect it all back up.

At last, I put everything back inside the case and closed it up. It still is as broken as before, but at least it's still usable. The next thing I'm gonna try is to reverse engineer the communications between the IC on the main board and the driver IC for the display to see if I'm able to figure out the protocol it's using (I suspect something like UART, but I'm not sure). If this works, I'm going to look for a replacement for the hole screen including the PCB, and if I'm not able to find one, I may try to design one myself. I'm going to cover this in greater detail in one of my upcoming posts.

Anyway, I hope you have a great day, and see you soon!