I have a TDS510A and a TDS644A and they are almost identical. Ofcourse the acquisition board is different, but the basics are still the same. Tektronix always re-uses a design as much as possible. If you stop at 'this schematic says 520B and my scope says 544A' then the schematic is useless to you. However, for creative people it provides a huge help to repair their scopes.