Homebrew, open source, repurposed, hacked, software defined, open hardware

Monday, 14 July 2014

Printer/Scanner film adapter EL wire (CCFL) inverter extraction

Some useful E-waste in the form of a Canon printer/scanner with a film adapter in the lid was pulled apart.

As well as some DC motors, shafts, screws, springs and plastic panels, an EL wire (CCFL) light source was found in the lid that served as a 35mm slide or 35mm film trans-illumination source.

The first step in awakening the light source was to establish the polarity of the two wires going to the CCFL inverter module.

The two lower voltage wires which ran to the CCFL inverter from the printer's main PCB were grey and black, and the high tension wires going to the EL wire were pink and white.

The circuit board of the inverter had no markings to indicate the polarity of the lower voltage grey/black pair, but a transistor near the low voltage grey/black input jack had its emitter marked on the PCB, and this was common to the grey wire.
Further inspection of the PCB traces confirmed that a nearby electrolytic capacitor's negative lead was common to the emitter and the grey lead, making the grey lead GROUND, and the black lead POSITIVE.

A variable voltage DC supply was connected to the leads and the voltage slowly increased. Half the CCFL panel lit up somewhere in the order of 15V, and by 24V it was fully lit.

This was consistent with one of the DC voltage produced by the AC->DC SMPS module in the printer being 24V, with no 12V or 5V options.

At 24V DC, the inverter was drawing around 200mA. The plastic surround will be retained and a small lamp is planned in conjunction with a spare 24V wall wart / DC plug pack.

Maybe someone pulling something similar apart will find this useful and possibly avoid destroying their inverter if it has similar BLACK=positive wiring.

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