Replacing the backlight on a BeoLink 7000

Replacing the backlight on a BeoLink 7000

A common issue on the BeoLink 7000 is a weak or absent backlight, as seen in the picture below.
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The backlight in the BeoLink display originates from a white Electroluminescent Backlight Foil (EL Foil) placed behind a blue-transparent LCD. It has a typical lifespan of ~3,000 houses, or around 125 days, so the light density usually decreases due to its age.

This guide will show you how to replace the backlight with a new one. The replacement can be bought here.

Please ensure that you have set up a proper ESD-safe environment before disassembling the BeoLink 7000. Older hardware is more sensitive and less protected against ESD.

First, remove the battery to ensure that nothing is shorted while working with the BeoLink. Remove the screw on the battery lid and desolder the battery.

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Remove the IR cap to access two of the four screws you need to remove to release the front glass plate.
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Remove the last two screws afterwards.
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Note that the front glass plate is now loose and make sure not to drop it when flipping the BeoLink.
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Remove the glass plate and ensure that the square corner nuts don't fall out.
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I measured the backlight AC voltage to be ~83VAC, but it should be around 110VAC, as specified in the manual.
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Disconnect the display and keyboard PCB from the CPU PCB. Make sure that you don't bend or crack the flat flex cables. You have to remove all 3 cables.
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Disconnect the keypad PCB from the display PCB by removing a single flat flex cable found at the top of the display PCB.
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Slide the two plastic fixing rails to the left and remove them to release the front frame. They can be tough to get off since they hold the elastomeric connectors in place. 

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Unfold the display. Note that the elastomeric connectors are fixed in place with pressure from the frame and the sliding rails, and that they might be hard to detach. The elastomeric connectors are the actual wires from the PCB to the display. Don't touch the surface, and by all means, do not remove the elastomeric connectors from the glass part. 
Please note the locations of the connectors on the PCB, as they must be positioned in the same spot when assembling the display.
If the connectors get misaligned or contaminated with dust or grease, you might get faulty readouts on the display.

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Desolder and remove the old EL foil. It's fastened with two pieces of double-sided tape. Remove it with care.
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Comparing the old backlight foil with the new foil. The new foil is seen at the bottom. There's still a protective film on top of it.
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Testing the new backlight. Looks good!
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The new backlight foil can then be reattached in the same position with two pieces of double-sided tape on the back, and the leads can be soldered to the display PCB.

The contrast is adjusted before assembling the BeoLink, using the potentiometer seen in the lower-left corner of the image below.
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When assembling the BeoLink, you'll find two wires providing AC to the display. The brown and black ones, as seen in the image above. They need to be located in a very specific way inside the BeoLink. If not, you'll have a hard time fitting the glass plate correctly. The image below should give an idea of where to put the wires.
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And the results. Just as we want it.
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This is not a complete restoration of the BeoLink 7000. After replacing the backlight, the capacitors and battery also need to be replaced. I will cover that in another post.

If you have any questions, please don't hesitate to contact me. Let me know if you need the backlight foil.

Related PCB

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