RD53 failure modes

[Fred Cisin]

On Fri, 7 Feb 2020, Carlos E Murillo-Sanchez via cctalk wrote:
> system originally came with an RD53 that has sat elsewhere for 25 years.  It 
> passed a read test in 2005.  So I tried to see if I could read it and maybe 
> image it now, but no go. The disk spins up, initiates a seek (the arm is not 
> stuck in a gooey stop pad; I've read that this is a common failure mechanism 
> for Micropolis 1325's; I opened it and saw the arm move) but then the arm 
> returns violently (clacking) to the rest position; it does this a number of 
> times (two to four, usually) and then it spins down. Applied voltages and 
> currents remain ok as this happens.

If nobody speaks up who actually know anything about them, . . .

Q: Is the return to the reset position more violent than the usual return?
If it is not different, then consider the possibility of something not 
related to positioner, such as: seek to track, try to READ, FAIL, reset, 
REPEAT.  In which case, it could be anything that caused the read to fail, 
such as head problems, failing to find the servo data, . . .