What can I try to fix this display?

LED display

I assumed water vapor got into it from opening and closing the fridge door so I tried these things:

  • I disconected it and left it in the sun for 4 hours.
  • I resoldered the display pins.
  • I heated it with a heat gun.

After all this nothing changed. You can notice that on the right it says 7; that 7 is probably a 3. Also, in the top right corner, next to min, there are two ticks half lit. On the left it shows -18. I know this because only on -18 the e letter (economic) is lit. The e letter, quick freeze, quick fridge and ! signs work properly.

This is the second display. The original one laster for 1.5 years. This one lasted for 5 months. I could just call the company to change it again but I'm sure it will do the same.

What can I try to fix this display? How does the display look on the inside?

  • \$\begingroup\$ The most important question is: are the LEDs really damaged (that is, they don't light up if you run a current through them by external means) or is the driver chip broken (we can not see it, I would assume it is a COB). In the later case you might feel fancy and replace it by your own µC driven PCB ;) \$\endgroup\$ – PlasmaHH Aug 4 '15 at 12:55
  • \$\begingroup\$ the LEDs work, because somethimes they light up and other times they don't. \$\endgroup\$ – GoTo Aug 5 '15 at 10:44
  • \$\begingroup\$ yeah, that sorts out an intermittent problem on the led board... or does it? \$\endgroup\$ – PlasmaHH Aug 5 '15 at 10:54
  • \$\begingroup\$ @GoTo That doesn't necessarily mean anything. Broken bond wires in the module, or defective board under the chips inside the module can very easily explain that as well. But you're welcome trying 3V 5mA limited probing around on the block's pins. Since it's bust already anyway. \$\endgroup\$ – Asmyldof Aug 5 '15 at 12:17
  • \$\begingroup\$ @asmyldof it's not bust. The PCB you see in the pictures controls the whole fridge: reads temperature sensors, controls the motor, controls a valve. That is working properly. I will try to resolder all the components on the PCB because it seems the led module should be ok. \$\endgroup\$ – GoTo Aug 5 '15 at 18:15

This is likely a design flaw that needs to be adressed by the manufacturer. LED displays like these, when not mistreated should last for 50000 hours continuous illumination (5.7 years) at the least, when no cost or corners are cut that number goes all the way to and/or beyond 200000 hours (22.8 years of always on for each LED).

Either the module is so cheaply made that moisture can creep in and permanently damage the chips, or there are mechanical stressed damaging bond wires, or, etc etc etc.

Proper modules are cast in the right kinds of resin for the use they are made for, this one isn't. That's all there is to it.

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The internal construction of those modules consists of a PCB inside the white plastic (the black is ink) with pins coming out the back and LED dice wire bonded directly to the PCB on the front. The white plastic forms the outside of light pipes from each die to the surface. The entire part is filled with water-clear epoxy, filling the light pipe channels from the front surface and embedding the PCB completely so that only the pins protrude out the back. The LEDS would be connected in a multiplexed configuration to save pins and drivers.

Here you can see a similar display with a 1/2 yuan coin for scale:

enter image description here

They are not practically repairable in any way, and I agree 100% with @Asmyldof (+1) that this is a manufacturing issue and should be fixed for you at no charge.

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    \$\begingroup\$ thanks a lot! I thought about opening it but I had a hunch it will be sealed off. \$\endgroup\$ – GoTo Aug 5 '15 at 10:51

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