To answer your question so that it makes sense, I'd first like to provide some background...
In the Plus Hardcard 20, when the disk is off, the heads are parked, resting on the platters, in a landing zone near the hub of the drive. To prevent mechanical damage to the platters, the head actuator is locked in place by a spring loaded latch.
Normally, when the disk starts, one of the first things it does is spin up the platters. As the platters spin up to speed, they create sufficient air movement to actuate an air vane which moves against the spring force holding the head actuator latch, thereby releasing the head actuator.
The 'stiction' problem that is common to Hardcards arises from the deterioration of the coating of the disk platters. When the coating deteriorates, it often becomes sticky. Since the heads and platter are polished super smooth, it takes very little to make them stick
together. When the heads are sitting parked on the platter they settle into the adhesive surface and stick.
If the head is stuck securely enough to prevent the drive motor from spinning the platters, the drive will not initialize and the dreaded 1701 error will appear.
If only a single head is stuck, often times a warm up period will soften the 'adhesive' and repeated rebooting will nudge it loose and allow the drive to spin up.
When that doesn't work, there are two other techniques that are often effective in freeing a stuck head:
1) Place the drive on a smooth surface and apply a sharp flat spinning motion. This can often free the head by using the static inertia of the motor and platters to spin the platters relative to the heads. If that doesn't work...
2) Hold the drive in one hand and apply a sharp strike with the heel of your other hand to one of the long edges of the drive. This will use the inertia of the head actuator and counterbalance to move the heads slightly (within the limits of the head actuator lock).
External forces used to loosen the stuck head will only provide temporary relief. The deterioration will continue, other heads will start to stick and eventually the friction from multiple stuck heads will cause the drive to stop responding to 'percussive maintenance' or other tricks.
I've dealt with quite a few of these things over the years and I'm sorry to say the gradual worsening of the condition is inevitable and failure unavoidable. Use whatever tricks you can to get the disk started and backup your data. That drive is going to fail. If you don't
have access to a Class I clean room, you can't really repair it. Opening the drive to 'fix' it should only be used as a last resort to try and recover you data before you trash the drive. It will not last.
The photos below show evidence of 'stiction' (the actual footprint left on a platter by a stuck head) and the head actuator lock from a Hardcard 20 (so that you can see how the long edge impact would move the actuator).
