Beomaster 8000: Step Five (2) - Rebuilding the Displays and Indicator Lights with SMD LEDs

This is a continuation of this post about rebuilding the display board of a Beomaster 8000:

After 24 hours the LEDs were all still in business, and so I decided to put the displays back together. My current method is to press the display covers onto the PCBs with carpenter clamps and then use black hot glue to seal the sides of the display units. This keeps them together reliably, while it is still reversible - with some effort the glue can be peeled off to open them again. I like solutions like this since no one (and no electronic component) is 100% perfect, and so it is nice if one can repair things (again) at a later date if necessary.

After putting the displays back together I usually run them for another 24 hours to make sure that the assembly process did not inflict damages on the SMD LEDs:

While this test was running, I did the rest of the display PCB. I replaced the two electrolytic capacitors with 105C grade Japanese units and then I went on to replace the four incandescent light bulbs that illuminate the indicators (clipping, filters, mono, and manual tuning). This shows the right two bulbs in their reflector boxes:

The original bulbs usually have very weak leads since they corrode over time. The slightest motion of the bulbs can break them off. Therefore, I developed a SMD LED based solution to replace them. This shows them in place of the bulbs with the reflector box removed:

There need to be two versions of these SMD LED boards since the reflector cases are mirrored for the left side, i.e. the polarity is reversed (which plays a role for LEDs while bulbs are impervious to the current direction): 

And here with the reflectors put in place:

After the 24 hrs test I soldered the displays back into the PCB:

Before I test this board in situ I will restore the microcontroller board...more about this in the next post of this project.

Beomaster 8000: Step Five - Rebuilding the Displays and Indicator Lights with SMD LEDs

No Beomaster 8000 restoration is complete without rebuilding the displays. They will all fail eventually, and most in the near future. And since those beautiful large LED displays are a main design feature of this lovely receiver, nothing is more frustrating than having a few missing segments. No matter how good the condition of the enclosure, when the displays are not complete it just looks sad! Not beolovely at all!

Luckily the displays are large enough that one can update them with 0603 packaged SMD LEDs, which can still soldered fairly well by hand. For this to happen one needs to extract the displays from the display board:

Once liberated, the next step is to open them up and scrape off the original LEDs, which are directly bonded to the PCB...truly a 1980s design!:

Once the pads are prepared it is time to line up the SMD LEDs and solder them into the places of the original LEDs:

The critical element here is to place the SMD LEDs precisely into the areas that are underneath the light guides in the LED assemblies (white parts with long slots in the picture above) when assembled. If they are not centered, the LEDs will get damaged during re-assembling the displays since the light guides will exert lateral pressure on the LED packages, which can result in them breaking off their pads. I do this by soldering the LEDs on only one side, then checking where the LEDs come close to the light guide slot walls, and then I correct the position of those that are a bit off. Once all are properly in place, I solder them on the other side.

After soldering all the LEDs in, it was time to give the boards their first 24 hrs test. For this I have a breadboard setup that mimics the wiring on the display PCB:

Let's see if they are still all on tomorrow!