Hi all. I've ordered some days ago a faulty LC2 dimmer at good price from a guy of this forum (thanks to him).
symptoms: the touch was working but not the IR
Here is my repair story if it can help someone.
here is the faulty board
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you can see the IR board on a little PCB.
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the system is connected to the main so you must disconnect it from the mainboard to work on it
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and use a power supply to safely test the circuit.
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the PCB uses 3 pins. two for power and one for received IR burst.
the ground is the black the red is the +5v and the white is the output
here is the schematic from the service manual
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using a scope and after powering the circuit under 5v I've got this trace at the output
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With or without IR light from a remote there's some random burst -> stange so I'm trying to find where the IR light is stopped.
Here is the trace at the point A when pushing a button on the remote
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Well the bursts are received by the photodiodes.
now at the point B i've got
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So the discrete 455KHz tuned amplifier works too
and now at the point C
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huh! nothing! Huston? we have a problem! the U2506 input has an offset and seems to have a low input impedance.....
ok now let's check the other signals. test the ref voltage at the point D
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Wow! noisy ref voltage! even if we are near the 2.35v value from the datasheet there's definitively something wrong!
looking closely to the PCB something was strange:
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with the binocular
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the capacitor pin was corroded -> electrolyte leakage! here is the culprit! The leakage has corroded the capacitor copper pin and the ref voltage is no more filtered
Eeven taking lot of care when removing it the ground pin was torn from the PCB
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the capacitors are two 22uF 6.3V with 4mm diameter
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and 5.5mm heigh
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I've found a good replacement from Panasonic FK serie 105°C even if the original one is a standard (not low ESR and 85°C)
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after modifying the copper to reconnect the ground of the capacitor (removing green varnish)
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the capacitors were replaced with a ground wire
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now here is the reference voltage measurement at point D
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Well! much better!!
and now the output signal of the IR board with IR signals coming from the beolink1000
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It's alive! the circuit is now working!
we can close the metal shield
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put it back on the main PCB and voilà!
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the dimmer is now working well \o/
I hope this post will help someone :)