Ok, so i have this old frequency counter, which would be perfect for trimming the keyboard but is also kind of dead. When i try to measure a known good source i only get a bunch of zero's and from time to time some flicker.

Luckily there is an easy to obtain service manual with a self test procedure and schematics (Yes they did this in the 80s, crazy right).

So i popped off the lid and followed the manual.

1. open Device - "Allready did that."
2. remove Jumper to get device to test mode - "Easy!"
3. set switch on backside to 'use internal clock reference' - "..... Yeah, ... i should do that."

Turns out if you want to use an external reference source you kinda need one ... uppsi.

After setting the frequency counter back to its internal reference it worked great. I wonder if that was the reason why it was thrown out by its previous owner.