I have an FA that I bought used around 20 years ago. It worked very well then. Few years ago I shot some film and the exposures were all off.

I recently took out the FA and found that the meter works perfectly, EXCEPT it is OFF by 3 stops. I calibrated the meter using a digital camera and the sunny day f/16 rule.

Basically, if I am using ISO100 film, I have to set the camera to ISO800 to get the correct exposure readings. This is very consistent and is true for both center weighted and matrix metering modes.

Does anyone know what the issue is? The metering photodiodes getting old? Or something dirty or a film got on the metering diodes?

I found the TTL flash diode but cannot find the metering diode. Can anyone tell me where it is?