More on differences between US and European versions of 2501 card reader (model A1/A2) power supply

THE OBVIOUS FIRST

The mains voltage and frequency are different between the two geographies, which leads to the need to change the transformers and some attached components. Due to the magnetic saturation characteristics of the iron core in the transfer, the size and design varies based on frequency, with 50Hz transformers generally larger than their 60Hz counterpart. 

In the US, the mains frequency is 60Hz and the voltages one might encounter are 115V, 208V and 230V. Buildings whose supply is three phase would generally provide 208V as the phase to phase voltage, whereas single phase (residential style) utility connections provide 230V and 115V. 

In Europe, mains are more standardized at 220V but there is an acceptable range above and below, thus the need to adjust for mains voltage as low as 195V and voltages above 220V as well. 

The transformers IBM uses in their mainframes supported machines attached to all of the usual US voltage levels, thus they had taps for 115V, 208V and 230V which were configured during installation to match the building mains voltage. The transformers used in European machines generally had taps for 195V, 220V and 235V instead. 

CONFIGURING TRANSFORMERS DIFFER BASED ON REGION

Given the difference in the transformers installed in the machines between regions, the terminal blocks where the installer would configure the voltage change. Making this even more complicated, the transformers used by IBM might have more than a single multitapped primary winding. In that case, jumpers would connect parts of the two sets of windings so that the net magnetic drive was appropriate for the target voltage. 

Below is a transformer inside the IBM 1130 is wired for 115VAC input, along with the chart that describes the wiring needed to configure for 115, 208 or 220V.

Below this is the European equivalent of the same transformer in the IBM 1130, shown wired for 195V with its chart. 

This explains the wiring diagram for the European version of the 2501 model A2, which used terminals 1 to 4 on PSTB1 terminal block. Unfortunately, the actual connections show that it uses five terminals, similar to the US dual primary winding transformers, and couldn't just implement the chart just above for 115, 208 and 230.

SPECULATIVE WIRING OF US TRANSFORMER TO TERMINAL BLOCK PSTB1

My first guess at the connections of the transformer primary windings to terminals 1 to 5 is below. This matches the US transformer type from the US IBM 1130 and would be consistent with the jumper between terminals 2 and 3. 

In order to validate this guess and make a change to 220V, I will disconnect the terminals and measure resistance to try to verify (or disprove) the wiring concept. I will also look at where the line connections are made to see if that is consistent with my speculation and a 208V setting.