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Tuesday, September 2, 2014

Beomaster 8000: Rebuilding the Displays with SMD LEDs

I saved the final restoration task until the end. The Beomaster 8000 displays are one of the major trouble spots, and this Beomaster needs to survive a long journey to Australia. So we decided to rebuild all four display units with surface mount (SMD) LEDs to ensure that the displays will still work post-shipping.

As usual I took out the display board for easier access to the solder points of the displays:

It is advised to use a desolder gun for taking the displays out, since all display pins need to be loose before removal of the displays. Trying to do this with copper braid is not advised. So I took my trusted Hakko 808 to it and removed the displays:

Then I removed them from their plastic alignment supports:

And opened them up. this is done by cutting off the plastic tabs protruding out of the bottom of the circuit boards with a sharp knife (take care to not damage the traces...):

The next steps were to scratch off the old LEDs (here also caution is advised to not damage the traces). And then, after a thorough cleaning with ethanol it was time to solder the SMD LEDs on:

It is imperative that the LEDs are well-centered on the pads that the white reflector masks can fit on without straining the LEDs and without gaps between the masks and the circuit boards (otherwise, light will penetrate from below into adjacent, potentially off segments and make them light up partially...an ugly effect).

After I completed the job I set the displays up for testing on a breadboard. I usually run them for 48 hrs before putting the displays back together. I also test them for stability by trying to wiggle them with a toothpick left and right to see if the solder joints are good. One of the issues when soldering the LEDs is that the boards do not have a solder mask, hence the solder tends to flow away from the components, which can cause problems. This can be counteracted somewhat by heating the part first, then the pad, but nonetheless, this must be kept in mind during this procedure.

So far so good! I'll be back in a couple of days and let you know how this test went...

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