A Permanent Backlight for the Sony ICF-SW7600G

The Sony ICF-SW7600G portable synthesised-tuning world radio features a green LED backlight which illuminates the LCD screen when the "Light" button is pressed. In order to save battery consumption, the LED is designed to fade after a few seconds. This modification allows the display to be permanently backlit whenever the radio is switched on and connected to an appropriate regulated 6VDC power supply.

When the "Light" switch, S202, is pressed a positive voltage is applied via R316, 1kohm, to charge C206, 47µF. This charge then slowly drains to earth via R313, 680kohm. The decaying voltage is applied to Q307 and Q306 which control the brightness of D201, the backlight LED.

The modification comprises a high-value resistor (100kohm or greater) connected in series with a diode between the external power socket and S202/R316, which ensures that there is always a voltage across C206, and so the light is always on.

Take a high-value, low power resistor (the value is not critical - anything between 100kohm and 1Mohm will work) and a small general purpose diode such as a 1N4148. Snip one of the leads of the resistor and the cathode lead of the diode (usually marked by a band on the encapsulation) to about 1cm in length and solder the two together. Similarly shorten the anode lead of the diode and solder it to a length of single-core insulated cable (see Fig. 1). Slip a piece of sleeving over that joint and another over the long lead of the resistor. Slip a 3cm length of heat-shrink sleeving over the resistor and diode and apply heat to shrink it.

After removing the batteries from the radio, remove the five fixing screws (marked =>) in the rear of the case and remove the pcb assembly from the case. Using a thumbnail, prise open the fixings (marked with red arrows in Fig. 2) that hold the speaker and display board. With the speaker withdrawn to the full extent of its cable it is now possible to turn over the display board (see Fig. 3).

Fig. 3

Position the resistor to the right-hand side of the LCD panel (see Fig. 2) and dress the sleeved lead to the bottom-right of C219 and fold it over the edge of the board adjacent to S202. Cut the sleeving to length and solder the lead to the top-right-hand terminal of S202, marked with a white arrow in Fig. 4.

Fig. 4

Dress the connecting cable as shown in yellow in Fig. 2 below the LCD panel and round the multi-way ribbon connector. Dress it inside the speaker mounting posts and down towards the bottom of the chassis adjacent to the case fixing hole. Feed it to the rear of the chassis and towards the yellow power socket taking care to dress it clear of the case fixing hole (see Figs. 4 and 5). Solder the wire to the terminal of the power socket between R524 and D503, marked with a white arrow in Fig. 6.

Fig. 5

Fig. 6

Check the wiring carefully and replace the speaker and the display board. When reassembling the case, ensure that the plastic switch activators in the case locate correctly with the switches on the pcbs. In particular, check that the power switch is in the "Lock" position, otherwise physical damage to S201 may occur.

The modification is now complete.

Plug in a 6VDC regulated power supply unit (PSU) to the yellow power socket (observing correct polarity - the centre pin is positive) and when the power switch is moved away from the "Lock" position the display light should come on. If you unplug the PSU while the light is lit, the display will dim slowly as normal on battery power.

Short-wave Radio Website Bookmarks   Stephan Großclaß's Sony ICF-SW7600G website Rick's Modster Madness

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Pembers' Ponderings

Compiled by Alan Pemberton
Sheffield, South Yorkshire, England
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