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This machine didn’t work.  There is a rubber belt which drives the print head.  It was totally gone and had to be replaced. The type and size of the belt does not seem to be very critical.

A worse part in the repair was the print head.  The head consists of seven electromagnetic drivers.  Each driver moves a thin steel wire inside a small flexible tube forward when it needs to print a dot.  At the end of the seven wires they are vertically aligned in a small plastic block.  

After years not being used, dried ink blocked movement of the wires inside there  tubes.  With alcohol, some moderate heat, some moderate force on the wires and a lot of patience they finally started moving.  Ink ribbons are not widely available.  I found a Dutch supplier who delivers worldwide and has a very wide collection of ribbons and other calculator and typewriter related supplies.  See Links.

Now, about a year later, the print head still functions flawlessly.

There are six  large PCB’s. Four are packed with a total of more then 200 IC’s, each IC containing a bit of logic. The other PCB’s include some power electronics to drive the print head.  It all still  works fine.  So does the core memory.

Below is a close-up of the print synchronisation wheel. It shows some but not all detail.

The P252 is the most capable calculator of the 249/250/251/252 series.  Internally the P252 looks very similar to the P249 of which a lot of information can be found at http://www.calcuseum.com/    Data sheets of the early IC’s used, can also still be found on the internet.

The print synchronsation

Wheel (source: Calcuseum.com)

The kind of early IC’s used

(own collection)

The print head

PCB with core memory

4 TTL logic PCB’s

PCB with power electronics

Power unit