LED brightness

The metering system in the T981 is a close copy to that in the Yashica FX-3. It has three LEDs for over, under and correct exposure. The over and under ones are red, the correct exposure one is green.

The PCB that carries the components has been redesigned from the FX-3 as the space available for it is different. But the circuit looks identical but with one exception. In the FX-3, three separate current limiting resistors are used - one for each LED. In the T981, there is only one which is common to all three LEDs. This is not ideal as red and green LEDs generally require different currents. Particularly, green LEDs require more current. This, I decided, must be contributing to the poor visibility of the green LED.

I bridged out the single resistor and, instead, fitted three separate ones. Fortunately there is an easy place to do this as there are links from the PCB above the rangefinder to the LED board. It was simply a case of replacing the links with resistors. Notes: make sure the resistors don't hinder the frame mask. With limited space available I found 1/8th Watt resistors were best.

After some experimentation, I decided on 470 ohm resistors for the red LEDs and 270 ohm for the green LED. With no information about the LEDs, I didn't want to reduce the values too low for risk of exceeding the maximum current for the LEDs.

As has been noted elsewhere, this wasn't a total solution. Although the LEDs are brighter, they are still difficult to see in bright conditions.

Update: Look at the 'In Use' page for how I finally resolved this.

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