Hi Matic E meter adjust

[Gradskater]

I have been scouring the internet looking for some info about the hi matic e meter. I have one that seems to be working, but no matter what I do it wont stay open for 2 sec (the long shutter speed). At asa25 and covering the metering cell it will only stay open for about 1/2 sec. Its got new batteries (1.4 zinc air).

I think there is a potentiometer somewhere under the top that might need adjusting. Does anyone have any idea what screw I need to turn?

thanks for any info!