HEre's a little information on how this works. The cassette drive interface is not too simple, with several signals doing multiple jobs (!). But anyway... There's an 8 bit shift register, IC2 (4015) on the cassette drive PCB. It takes clock and data from P44 and P43 of the slave CPU respectively. Bit 5 ((pin 12) and pint 6 (pin 11) of this shift register are the run and brake lines for the HP motor (HP = Head/Pinch = the motor that moves the head bracket). Bit 5 drives Q11 (2SC2532) which then drives Q6 (2SA1204). This applies voltage to thye HP motor. Bit 6 drives Q12 (2SC2532) which short-circuits the HP motor to brake it. But there's a bit more. The power to the mechanical side of the tape drive is regulated by Q3, Q14, ZD1 and associated components. The input to this is controlled by Q2, which is driven by Q8, which in turn is driven by P42 of the slave CPU. The idea is that a command is clocked into the shift register, then the power is turned on and the motors run, etc. To detect whether the head is loaded or not, there's a leaf switch called HSW. One side goes to chassis, the other is pulled up to VL by R38. It then goes into a 4066 chip, IC3, which is used as a dual 2-input multiplexer controlled by the same line that's used to clock the command shift register. Q17 acts as an inverter, 2 of the switches in IC3 are controlled by the clock line, the other 2 by the inverted clock line in the obvious way. Anyway, the head position switch is multiplexed with the tape counter optoswtich signal, and goes to P46 on the slave CPU. Now back to the mechanical side of things. The first problem is getting inside. The bottom cover of the cassette unit comes off with the obvious screws. The manual then says to peel off the trim on the cassette 'pocket', undo the 3 screws holding the chassis to the case and take the mechanism/PCB out. I seem to rememebr it's possible to get it out without removing said trim, but that it's a right fiddle!. Th manual also says that to remove the PCB you unsolder all the wires, take out the screws, and take off the PCB. Again, I seem to remember you have to desolder at least the write-protect switch, this is a leaf contact on the chassis, the tab of which is soldered into a hole on the PCB without a wire if you see what I mean. But you can leave the other wires connected. The HSW (HP switch) is fixed on top of the HP motor bracket with one small screw. This is the cylindrical motor at the front of the unit, not the flat motor at the back with the belt drive to the capstan flywheel. When refitting it, the manaul gives the adjustment as : Whit the switch removed from the HP motor : a) The moving contact (nearest the mounting hole) should be at right angles to the plastic block where the terminals go through. b) The gap between the the 2 contacts should be 0.35 +/- 0.1 (mm?) Then fit the swtich and c) The moving contact should be on the surface of the cam (cam positioned so it is on the low point od the cam) d) The plastci block on the fixed contact must be in contact with the boss on the HP motor bracket. With the swtich remobed, the HP motor assembly comes out with 2 more screws, one on top, the other underneath. Be careful when removing this not to disturb the 'P lever' (the lever that actually carries the head, etc). Your problem could be electronic or mechanical. I would start by disconnecting the HP motor wires and running the motor from a 3V battery. See if the head moves backwards and forwards correctly. And see that the HSW contacts are closing as they should do. Then we can go into troubleshoorting the electronics. -tony