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Tuesday, February 17, 2015

Beomaster 8000: Display Repair (II) - Installation of SMD LEDs and Test

After cleaning up the mess with the frequency display of the Beomaster 8000 that I am restoring right now, I went ahead and opened all displays and scratched off the old LEDs with a carpenter's knife. One needs to be careful when doing this since it is very easy to damage the traces with the knife edge. Here is a picture of the naked boards:

Now it was time to solder the SMD LEDs onto the pads. I am using LUMEX SML-LX0603IW-TR types. When doing this it is very important to remember that the LEDs need to fit under the masks that shape their light into the elongated 'segments' that make up the 7-segment displays. This requires precision soldering and a steady hand to make sure that the small 0603 parts are fully centered on the pads. Otherwise the mask will be obstructed and a gap results between the mask and the PCB that permits light out of the sides of the display. This results in an unwanted 'halo' around the displays that can be seen very well when the Beomaster is operated in a low-light environment.

For soldering I always line up the LEDs in same orientation in rows, so I can pick and place them efficiently:

Here is a picture of the frequency display after installing the LEDs:

And lit:

And here a picture of all of the displays in my test fixture:

Once I solder in the LEDs I usually run them for 24 hrs to make sure that there are no issues. Tomorrow, if this goes well, it will be time to close them up and re-install them on the display PCB.

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