The PT Too power supply is both complicated and simple....
You can split it into two parts:
- generation of the AC signals - complicated
- amplification of the signals and step-up to 110 V - simple
If there's a problem with the AC signal generation then you can almost forget about it as sometimes PT have rubbed off the chip numbers and anyway the chips aren't available. You can replace the reference quartz crystals and any capacitors to see if that blindly makes any difference. Mark Kelly's thing seems to be a replacement if the generation part is broken.
If it's the amplifier section or step-up to 110V transformers then that bit is easy as it's a circuit from the chip-amp datasheet coupled to the transformers via some output caps.
Try changing the output caps anyway - they're the same kind as on a Linn Valhalla and them going bad results in the same jittering motor syndrome (as far as I can work out from an experiential but ignorant point of view).
Still, not sure why that would only effect 33 and not 45.. Could be the circuit that cycles between the speeds - I wouldn't have a clue about that.
Or, there are many many Premotoc 110V motor power supplies out there for Linn,systemdek,Heybrook, PT Too - it's the same motor. so if simple and cheap fixes don't work just buy something else for £170+ .
I wonder, there must be some kid's toy out there that outputs sinewaves from some kind of 16 bit sample - technology that wasn't around in the PT Too days - that could replace the whole signal generation section and could be connected up to the final stages.