A quick reply, I think all seven boards are replacements, the manual from Artek is a little newer.
I can't see how they wouldn't work at a lower speed, with the 5MHz board in the correct position, just you wouldn't get the full 50MC.
David
I have the artek manual for the 5245L issued 1965. I have the service manual from BAMA or KO4BB for instruments serial prefix 628 as well. I see no signs of these board revisions. The artek manual however includes six revisions of the A15/A16 boards. And they state the two high speed boards to be used, maybe the boards 5212L-4A are even slower than the 600kc of the 05232-6016?
When I received the counter (serial prefix 408, clearly marked as defective) the higher speed board however was populated at the upper most digit, so getting the lowest frequency
![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
But board and nixie are defective, so I think he swapped the boards to get a 7 digit counter but broke the high speed decimal counter. Will try to fix the board (more than one digit is lighting) which should be doable unless the photocoupler assembly is bad.
On wednesday I get another 5245L with serial prefix 504, let's see what's inside
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)